Nature and Management of Tropical Peat Soils

Nature and Management of Tropical Peat Soils

Table of Contents

FAO SOILS BULLETIN 59

by J. P. Andriesse Consultant

Soil Resources, Management and Conservation Service FAO Land and Water Development Division FAO - FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 1988 Cover photo: Initial clearing for drainage of bush vegetation on deep peat in Brazil (photo: J.P. Andriesse) The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of Its frontiers or boundaries.

M-51 ISBN 92-5-102657-2 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior permission of the copyright owner. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director, Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy. © FAO 1988 This electronic document has been scanned using optical character recognition (OCR) software and careful manual recorrection. Even if the quality of digitalisation is high, the FAO declines all responsibility for any discrepancies that may exist between the present document and its original printed version.

1

Table of Contents Foreword Acknowledgements 1. INTRODUCTION 1.1 Objectives 1.2 The Definition of Tropical Peats 2. DISTRIBUTION OF TROPICAL PEAT 2.1 Extent 2.2 The Main Occurrences 2.3 Application of Research 3. FORMATION OF PEATS 3.1 Introduction 3.2 Environmental Factors 3.2.1 Hydro-topography 3.2.2 Source and quality of water 3.3 Stages in Development 3.4 Type of Vegetation 4. THE MAIN CHARACTERISTICS OF TROPICAL PEATS 4.1 Introduction 4.2 Physical Properties of Organic Materials 4.2.1 General 4.2.2 Moisture relationships 4.2.3 Bulk density 4.2.4 Porosity 4.2.5 Texture and loss on ignition 4.2.6 Swelling and shrinking 4.2.7 Irreversible drying 4.2.8 Physico-chemical properties 4.3 Chemical Properties of Peat Materials 4.3.1 Introduction 4.3.2 Composition 4.3.3 Acidity 4.3.4 Exchange characteristics 4.3.5 Organic carbon 4.3.6 Nitrogen 4.3.7 Phosphorus 4.3.8 Free lime (CaCO 3 ) 4.3.9 Sulphur 4.3.10 Trace elements 4.4 Biological Activity 4.5 Characteristics of the Peatswamps 4.5.1 Geomorphology 4.5.2 Hydrology 2

5. CLASSIFICATION 5.1 Introduction 5.2 Historical 5.3 Classification Systems 5.3.1 Introduction 5.3.2 Topographical classification 5.3.3 Classifications based on surface vegetation 5.3.4 Classifications based on chemical properties 5.3.5 Classifications based on botanical origin 5.3.6 Classifications based on physical characteristics 5.3.7 Classifications based on genetic processes 5.4 Conclusions 5.5 Recommended Approach 5.6 Classification of Organic Soils According to Soil Taxonomy 5.6.1 Introduction 5.6.2 Fibrists 5.6.3 Hemists 5.6.4 Saprists 5.6.5 Folists 5.6.6 Further development of soil taxonomy for the Tropics 5.7 The Classification of the Physical Environment 6. AGRICULTURAL POTENTIAL 6.1 Introduction 6.2 General Suitability for Cropping 6.3 Land Capability and Crop Suitability Evaluation 6.3.1 Introduction 6.3.2 The initial survey 6.4 Conclusions and Recommendations 7. RECLAMATION PROBLEMS 7.1 Introduction 7.2 Initial Problems in Peat Reclamation 7.2.1 Initial drainage 7.2.2 Clearing 7.2.3 Burning 7.2.4 Organization 7.3 Permanent Constraints in Peat Reclamation 7.3.1 Subsidence 7.3.2 Cultivation practices 7.4 Water-table Management

3

8. AGRICULTURAL MANAGEMENT 8.1 Introduction 8.2 Crop Choice 8.2.1 Choice of crop under natural drainage conditions 8.2.2 Choice of crops under improved drainage with water-table at less than 40 cm depth 8.2.3 Choice of crops assuming deep drainage 8.3 Water Management at Farm Level 8.3.1 Systems of open drains 8.3.2 Subsurface drains 8.3.3 Irrigation 8.4 Tillage and Cultivation Methods 8.5 Correcting Acidity by Liming 8.5.1 Lime requirements 8.5.2 Materials used 8.6 Fertilizer Use 8.6.1 Introduction 8.6.2 Burning 8.6.3 Basic principles 8.6.4 Nitrogen requirements 8.6.5 Phosphorus requirements 8.6.6 Potassium requirements 8.6.7 Calcium and magnesium requirements 8.6.8 Micro-nutrients or trace element requirements 8.6.9 Conclusions 8.7 Crop Protection 8.7.1 Weed control 8.7.2 Pest and disease control

4

9. ENERGY USE OF PEAT 9.1 Introduction 9.2 Peat as an Energy Source 9.2.1 Decomposition stage 9.2.2 Carbon and hydrogen content 9.2.3 Ash content 9.2.4 Types of fuel peat 9.2.5 Fuel properties 9.2.6 Minor factors 9.3 Resource Estimation 9.3.1 Initial survey 9.4 Peat Production 9.4.1 Introduction 9.4.2 Clearing 9.4.3 Ditching 9.4.4 Clearing of stumps 9.4.5 Methods of production and layout 9.5 Peat Extraction and Land Use Planning 9.5.1 Rapid disposal 9.5.2 Slow disposal 9.5.3 Effect of peatland distribution 9.5.4 Reclamation of freshly exploited peat deposits 10. ENVIRONMENTAL ASPECTS OF RECLAMATION 10.1 Introduction 10.2 Natural Functions of Peatswamps 10.2.1 Regulating functions 10.2.2 Production function 10.2.3 Information function 10.2.4 Miscellaneous functions 10.3 Environmental Impacts of Peat Reclamation

5

REFERENCES AND BIBLIOGRAPHY APPENDIX 1 - Tests of Organic Soil Materials APPENDIX 2 - Volumetric Relations in Soil Materials APPENDIX 3 - Soil and Other Physical Limits for Satisfactory Crop Growth on Organic Soils APPENDIX 4 - Linking Drainage and Soil Temperature FAO SOILS BULLETINS

6

Foreword In developing countries at the present time there is an increasing demand for agricultural expansion onto new land caused by population pressure, by deterioration of existing land as a result of overfarming, or by competition for land from industry and urbanization. For many countries self-sufficiency in food either necessitates intensification of food cropping on existing land or the reclamation of new land for agriculture. Most land not yet in agricultural use has some limitations on its suitability for agriculture. Much of this land is too steep or too wet for farming. In general the limitations caused by wetness are technically easier to overcome so wetlands offer better prospects for sustained agriculture than steepland. Wetlands have been developed as farmland ever since the very earliest agricultural settlements and the most suitable and some less suitable land has been occupied for centuries. Many undeveloped wetlands have serious limitations of which the presence of thick deposits of organic material or peat is but one. A prerequisite for the successful farming on wetlands is the provision of an effective drainage system to create sufficiently well-aerated soil conditions to allow crop growth. In this respect peatswamps are no different to other land. Their reclamation however, often leads to unforeseen problems which are usually a result of the lack of understanding of their underlying causes. There is relatively little experience of the reclamation of peatswamps in tropical countries particularly those in the developing world. As well as providing farmland after reclamation peatswamps have a potential for peat extraction if the peat is of good quality. Peat can provide an attractive source of energy particularly in remote areas and in countries that depend entirely on outside fossil energy resources. For this reason the last few decades have seen many attempts in the tropics to tap such resources, with mixed results. Unfamiliarity with the conditions of the swamps and the nature of the peat materials, among reclamation engineers and farmers alike, has caused many failures. Often, disappointments could have been avoided if the knowledge of appropriate reclamation procedures and suitable agricultural management specifically geared to peat soils had been readily available. Considerable knowledge has been acquired both through reclamation efforts in temperate countries over the last few centuries and to a lesser extent, more recently in the tropics. Some problems caused by peat reclamation cannot be solved. One of them is the fact that peat once drained will gradually disappear, so sustained agriculture on peat is a fallacy. This Bulletin aims to consolidate the up-to-date knowledge available on the characteristics of tropical peatswamps, and to describe the management required to reclaim them and to bring them into production. It is comprehensive and intended for all disciplines involved in peatswamp reclamation. All aspects of peatswamps are covered, from their genesis to the environmental impact of their reclamation on neighbouring ecosystems. This Bulletin is not a working manual in the sense that it provides answers to all problems which might arise. The subject is too wide in scope and the conditions too variable to make this possible in a volume of this size. The Bulletin tries to focus on principles, processes and procedures to create awareness of the likely problems involved, and to show ways and means to solve them. It also provides a carefully chosen bibliography covering most of the issues raised.

7

Acknowledgements In the preparation of this book the author has drawn on information from the traditional literature. In addition he made much use of personal experience not previously published. He has also received much assistance from individuals and organizations possessing information of practical value not so readily available. He would like to acknowledge the help of the Consultancy Bureau of Euroconsult in the Netherlands, and Bord na Mona in Ireland. He wishes to thank in particular Professor Snyder, University of Florida, U.S.A. (Everglades Research and Education Centre Belle Glade) for making available research data from the Everglades Peats, and the Departments of Agriculture in Sarawak (Malaysia) for also allowing him to use unpublished information. The text was edited by J.M. Hodgson and R.C. Palmer of the Soil Survey and Land Research Centre, Rothamsted Experimental Station, England.

8

1. INTRODUCTION 1.1.Objectives 1.2.The Definition of Tropical Peats

1.1 Objectives The title of this Bulletin poses questions about the definition of peat. What are in fact Tropical Peats and why should they be treated specially? Why are they not regarded as similar in all respects to peats at higher latitudes in the cool temperate and boreal regions for which efficient management procedures are known? There are indeed many reasons why peats in tropical regions should be given special treatment and these are elaborated in some detail below. Before the end of the 19th century it was not generally accepted in scientific circles that tropical peat existed and that it could form under the present tropical climate. Though peat and peatland in northern Asia and Europe has been used for centuries, albeit mainly for energy purposes, it was not until 1895, when Koorders published a description of extensive tropical peat forests in Sumatra (Indonesia), that it was established beyond doubt that peat soils could be formed under a tropical climate, and that they actually covered considerable areas (Polak 1952). Acceptance of this finding was facilitated by suggestions made by geologists somewhat earlier that the large coal deposits formed in the Carboniferous period are the remnants of enormous peat bogs of tropical origin in which the giant Pteridophytes (tree-ferns) were the main peat formers. This origin contrasts with that of present day peats in temperate regions, which are formed mainly from the remains of mosses and herbs. It should be remarked here that attempts to reclaim peat soils in the tropics date back several centuries. For example the Dutch attempted reclamation in the 17th century in the coastal strip north of Colombo in Sri Lanka, then Ceylon. No doubt unrecorded reclamation efforts were made elsewhere in tropical areas. Since the early description by Koorders, many peat deposits have been reported from tropical and subtropical areas, and it is now well known that organic soils cover extensive areas of the tropical regions, particularly on the coastal plains. Human settlement of such areas has up to now been avoided because reclamation has been constrained by several factors. Drainage problems, low fertility, risk of disease (for example malaria) and inaccessibility, kept the local population from developing them. Today, the accelerated pace of agricultural development to meet population growth and the need to expand onto peat lands, requires new management knowledge. Knowledge which is sadly lacking for most tropical areas. During the last few decades many attempts, often large in scale, have been made to bring these marshy lands into cultivation. There are many examples of success but there are more failures.

9

In retrospect it is easy to point out the many varied causes of failure. There has been a general lack of comprehension, which still persists in many quarters, that peat swamps are unique, as are the materials comprising them. The special character of the landscape and the underlying soils was often not recognized and reclamation followed the same pattern as for mineral soils. This frequently has had disastrous consequences: drainage soon deteriorated, flooding has increased in frequency and magnitude, nutrient deficiencies have occurred in crops and harvests have been poor. These are all reasons why projects and schemes have been abandoned. Peatland is being brought into cultivation at the present time on an increasingly large scale, particularly in South East Asia and Latin America, by small farmers and entrepreneurs who lack traditional know-how of farming on this type of land. For these reasons and in these circumstances it is necessary to look at the knowledge and management experience which have been developed and accumulated elsewhere. Such experience must be reviewed before it can be put to use in new localities. Any transfer of knowledge also requires sufficient basic information on the nature of the swamp to be developed and its organic materials. Such information also enables us to identify the need for specific research in cases where available knowledge is not directly transferable because of the specific nature of the peats involved. Chapters 2 to 5 of this book concentrate on ways of characterizing tropical peats so that management techniques can be matched appropriately in subsequent chapters. Because tropical peat reclamation is a relatively new field of development there is too little data and information. This needs to be put right by more research. The writer hopes that this Bulletin, apart from fulfilling its immediate objectives, will also generate sufficient interest in the subject to encourage scientists and project operators to make available their unpublished knowledge and practical experience. It is important to recognize that peatswamp reclamation will be successful only through integrated multi-disciplinary endeavour, encompassing civil engineering, hydrology, agricultural and social science. This Bulletin, however, does not focus in depth on reclamation issues or constraints of an engineering or socio-economic nature. Where appropriate, however, it indicates where such inputs are necessary so they are not forgotten. Peats and peatland are not only a resource for agricultural development. Extraction of peat for industrial purposes and its potential use as a local, relatively cheap alternative fuel, are gaining in importance as other fossil forms of energy are becoming an economic constraint to development. For this reason attention is given to peat as an energy source and to aspects of peat extraction, particularly in relation to agricultural usage and the agricultural potential of peatswamps after extraction. The agricultural or commercial development of peat and peatswamps requires recognition of the environmental issues which play a role when reclaiming tracts of wetlands. Peatswamps often provide unique ecosystems so environmental aspects must be reviewed where appropriate. Finally, a selected but extensive bibliography is provided for general reference. The author has made liberal use of the information contained in the literature. He has tried to refer as much as possible to this material, particularly when specific issues are raised or examples are used. For practical reasons it is impossible to acknowledge every individual source of information. Some of the original literature sources referred to by research workers could not be consulted and such sources have been acknowledged only by quotation.

10

1.2 The Definition of Tropical Peats Before embarking upon the treatment of the wide field of tropical peat soils and their management it is necessary to define the subject matter under discussion and to indicate its geographical limits. To start it should be recognized that the subject can be clearly subdivided into two: firstly the material itself, generally indicated as peat; and secondly its physiographic or geomorphological setting (the landscape units) which are given a wide variety of names but are generally known as peatswamps. These two aspects have received appropriate attention in the literature, but often in isolation from each other. Failure to recognize the need to study and manage the two entities together has been a reason for disappointing reclamation efforts. There is a very good historical reason why the two aspects have been studied separately. Peat, as a material, has been studied in the past mainly by chemists and geologists because of its potential for industrial or energy purposes. They have not studied it as a medium to plant growth in its natural condition and environment. Peat has received some attention in the past from horticulturists and gardeners, but the study of peat as a soil to be used for agricultural purposes and managed within a farming system or land utilization type is relatively new. The peatswamps, as physiographic units, have long been studied by biologists and related scientists and recently they have become a focus of attention for environmentalists. Here too there has been a strong input from biological science. From the above it should be clear that peat and peatswamp should not be considered as being synonymous and care should be taken to use these terms in their proper context. The situation seems even more complicated when the scientific terminology commonly used is analysed. To avoid misunderstanding and misinterpretation of the literature, it is necessary to elaborate on the exact meaning of the terms peat and peatswamp.

Peat Peat is traditionally defined as being synonymous with turf being partially carbonized vegetable tissue formed in wet conditions by decomposition of various plants and mosses. This restricted definition, including only materials which are entirely of vegetative origin, conflicts with several established soil classification systems. In older soil classification systems, peat soils are usually defined as soils having more than 65 percent organic matter. There is thus general confusion on the exact definition of peat and peat soil so modern classification systems, which we use in this Bulletin, try to avoid these terms. The term organic soils is used which covers a much wider range of materials than peat or peat soils as outlined above.

11

There are several reasons why, in this Bulletin, we adopt broader definitions than the traditional ones outlined above. First, apart from conflicting with existing soil classification systems, the adoption of the term peat soils with its restricted meaning would conflict with our objective, which is to indicate effective ways and means of reclamation and development of low-lying marshy or swampy lands. These, though largely peat, also include soils which are transitional between organic and mineral soils. Secondly, true peat (100 percent organic matter) has a low marginal potential for agricultural development so it would be illogical to devote a full bulletin to the management of such soils. Finally, areas of peat generally occur in association or in complex with soils in which the mineral component varies greatly. In general, the greater the mineral content the greater the potential for agriculture. A pragmatic approach is therefore needed and this justifies widening the area of interest to include all soils defined as organic soils. These are in general soils that have more than 50 percent organic matter in the upper 80 cm. They include soils which were termed muck, peaty mucks and mucky peats in the past. In general the terms peat, peat soils and organic soils are synonyms in this Bulletin, distinctions only being made where necessary. For practical purposes this means that the Bulletin encompasses all organic soils defined as Histosols in the US Soil Taxonomy (Soil Survey Staff 1975).

Peatswamps In the literature, peatswamps are frequently referred to as being wetlands, but as indicated by Schwerdtfeger (1980) a peatland classification is not the same as a wetland classification. The latter has a wider context and includes several types of which the most common are defined by Webster’s Collegiate Dictionary as follows: Wetlands Large or small bodies of open water surrounded by wet mineral soils as well as peatland. Moor A boggy area of waste land, usually peaty and dominated by grasses and sedges. Bog Wet spongy ground, poorly drained, rich in plant residues, having a specific flora such as sedges, heaths and sphagnum. Marsh A tract of soft land usually characterized by monocotyledons. Mire A marsh or bog. Fen Low land partly or wholly covered with water. It is clear from these definitions that all these wetlands could include peat, and to a wider degree organic soils. This may be why these terms are commonly used though they are almost synonymous, the choice being left to the individual. There is, however, some tendency for adoption of particular terms by individual disciplines. To some extent too, national or regional preferences are influencing this choice.

12

Tropical peats In broad terms there is no clear-cut scientific reason why tropical wetlands with organic soils should be managed differently from those in temperate regions. There are, however, practical differences between tropical wetland and other wetlands which influence management. The nature of the organic soils is different, because the plants from which the peat is formed are different. In the tropics, trees are frequently involved as opposed to sedges and sphagnum moss in temperate regions. The large wood content of tropical organic soils requires special management, particularly during initial reclamation. Perhaps of crucial importance is the difference in climate characterized by the high rainfall, high evapotranspiration, and very high mean annual temperatures in tropical areas. Surplus rainfall and high temperatures are perhaps the most important features distinguishing tropical peat areas from those of temperate regions. The climate has a direct bearing on peatswamp characteristics for example hydrology. It also has indirect effects on the peat itself through vegetation species. On the other hand, temperature has a direct influence on the rate of oxidation of the peat material. Climate has therefore an important influence when selecting management procedures. How do we draw the line between tropical and other peats? The characteristic woody nature of tropical peat deposits, the high precipitation and high temperatures do not necessarily coincide with geographical boundaries. If tropical peats were defined as being those between the tropics of Cancer and the tropics of Capricorn, it would leave out large areas of organic soils with features of tropical character. Soil Taxonomy (Soil Survey Staff 1975) defines tropical organic soils as those with isomesic 1 or warmer iso-temperature regime. This leaves out the organic soils of the midlatitudes (the subtropics) with mesic, thermic or hyperthermic temperature regimes. Such organic soils are in a sense intermediate between those of the tropical belt and those of temperate regions. They are agriculturally of importance and experience of reclamation accumulated for the last 50 years in various regions can be put to good use and transferred to the tropics. 1

Mesic. - The mean annual soil temperature is between 8°C and 15°C, and the difference between mean summer and mean winter soil temperature is more than 5°C at a depth of 50 cm or at a lithic or paralithic contact, whichever is shallower. Thermic. - The mean annual soil temperature is between 15°C and 22°C, and the difference between mean summer and mean winter soil temperature is more than 5°C at a depth of 50 cm or at a lithic or paralithic contact, whichever is shallower. Hyperthermic. - The mean annual soil temperature is 22°C or higher, and the difference between mean summer and mean winter soil temperature is more than 5°C at a depth of 50 cm or at a lithic or paralithic contact, whichever is shallower. If the name of a soil temperature regime has the prefix iso, the mean summer and winter soil temperatures for June, July and August and for December, January and February differ by less than 5°C at a depth of 50 cm or at a lithic or paralithic contact, whichever is shallower. Isomesic. - The mean annual soil temperature is between 8°C and 15°C. Isothermic. - The mean annual soil temperature is 15°C or higher but lower than 22°C. Isohyperthermic. - The mean annual soil temperature is 22°C or higher.

13

Based on such practical considerations, tropical and subtropical peats are defined by arbitrary boundaries at the latitudes 35 degrees North and South. This includes the whole African continent, most of South America, including the whole of Brazil and Uruguay where there are large areas of organic soils. Important peat areas in the southern states of Florida and North Carolina in the USA are also included. In Central Africa there are organic soils at high altitudes (over 2 000 m). It is debatable whether such soils with an almost temperate climate should be regarded as tropical peats, even though they are geographically found within tropics. They are, however, included since reclamation experience of these soils is badly lacking, and it makes sense on purely scientific grounds. In conclusion Tropical Peats, the subject of this Bulletin, are defined as all organic soils in the wetlands of the tropics and subtropics lying within latitudes 35 degrees North and South including those at high altitudes.

14

2. DISTRIBUTION OF TROPICAL PEAT 2.1 Extent 2.2 The Main Occurrences 2.3 Application of Research

2.1 Extent The extent of peat in tropical and subtropical regions, particularly in developing countries, is only known approximately. Estimates of total global resources of peat conflict for several reasons: i. Repetition of source error - Information is copied from the literature and accepted without checking or referring to the level of accuracy of the data supplied. ii. Mapping scale errors - Information is taken from small scale soil maps, such as the FAO/UNESCO World Soil Map at 1:5 million scale. Such maps can only show areas with organic soils if they are extensive. Smaller areas are frequently shown in association with Hydromorphic soils or Gleysoils without indication of the percentages of the organic components in the associations. In some cases the existence of an organic component is not distinguished at all. iii. Classification error - Mapping of organic soils depends on the local classification. Some countries only recognize organic soils if of significant depth or extent, others incorporate shallow mucky and peaty soils with hydromorphic soils. iv. Nature of source - Organizations mainly dealing with land evaluation for agriculture and organizations whose objective is the assessment of peat deposits for energy purposes, have different interests to serve and their mapping approaches often differ and are incompatible. As well as these basic sources of error figures are commonly misquoted because acres are confused with hectares (as in Ekono 1981, for the USA). Finally in some cases, where there is insufficient knowledge, rough estimates have been made by those supplying the information. Information from the developing world is frequently updated as is shown by the regular increase in reported extent of organic soils from such countries during recent decades. Table 1 summarizes known information on global resources of organic soils including those in tropical areas. Peats falling within the scope of this Bulletin are estimated in the last column. This data compiled by Bord na Mona (1984) has been checked against information from a variety of sources (Lucas 1982; Ekono 1981; Kivinen and Pakarinen in a report to the 6th Int. Peat Congress at Duluth 1980; Driessen 1977; Andriesse 1974) and in a few cases amended. The information, in particular that for tropical countries is likely to be revised as more reliable data becomes available. Present information indicates that throughout the world organic soils cover 436.2 million hectares of which 35.8 million hectares (8.2 percent) are in the tropics and subtropics. The area may be much larger. Kivinen and Pakarinen (1980) suggest that total global resources cover 420 million hectares and they believe that it may approach 500 million hectares. The author is inclined to agree with this because the resources of organic soils in the Amazon basin and in the wet equatorial belt of Africa are under-estimated. Table 2 gives estimates of the extent of organic soils in tropical and subtropical regions.

15

The figures in Tables 1 and 2 for South East Asia are probably over-estimates. In the author’s opinion, based on substantial experience in the region, the figures for Indonesia in particular tend to be exaggerated because they are based on air-photo interpretation. Subsequent mapping has revealed that much of the land interpreted as swamp is occupied by mineral soils. In Africa, Beadle (1960) indicates that in Uganda alone there are already 6 400 square kilometres of permanent swampland and as much land temporarily inundated in the wet seasons. Part of this land is likely to be peat, but how much can only be guessed. The study of peat resources in the Amazon basin is only just beginning but early reports indicate vast areas of organic deposits (Suszcynski 1984). There are 270 reported occurrences along the Atlantic coast of Brazil. This leads the author to believe that the total area of peat deposits in the tropical and subtropical belt will in the end prove to cover at least 40 million hectares constituting about 11 percent of the world total. Table 1 GLOBAL RESOURCES OF ORGANIC SOILS AND THEIR DISTRIBUTION (source Bord na Mona 1984)

Country

Area (ha)

Estimated % in Tropics

Western Europe Austria

22 000

Belgium

18 000

Denmark

120 000

Finland

10 400 000

France

90 000

FRG

1 110 000

Great Britain

1 580 000

Greece

5 000

Iceland

1 000 000

Ireland

1 180 000

Italy

120 000

Luxembourg

200

Netherlands

280 000

Norway Spain Sweden Switzerland

3 000 000 6 000 7 000 000 55 000 25 986 200

16

Eastern Europe Bulgaria Czechoslovakia GDR Hungary Poland Romania Soviet Union Yugoslavia

1 000 30 750 489 000 30 000 1 300 000 7 000 150 000 000 100 000 151 957 750

Africa Angola

10 0001 100

Burundi

14 000 100

Congo

290 000 100

Guinea

525 000 100

Ivory Coast Lesotho Liberia Madagascar Malawi Mozambique

32 000 100 -40 000 100 197 000 100 91 000 100 10 0001

Rwanda

80 000 100

Senegal

1 500 100

Uganda

1 420 000 100

Zaire Zambia

1 000 0001 100 1 106 000 100 4 856 500

17

Asia Bangladesh China Fiji Indonesia

60 000 4 200 000 30 4 000 100 17 000 000 100

India

32 000 100

Israel

5 000 100

Japan

250 000

Korea (DPR)

136 000

Malaysia Papua New Guinea

2 500 000 100 500 0001 100

Philippines

6 000 100

Sri Lanka

2 500 100

Thailand

68 000 100

Vietnam

183 000 100 24 886 500

Central America British Honduras

68 000 100

Costa Rica

37 000 100

Cuba El Salvador Honduras Jamaica

767 000 100 9 000 100 453 000 100 21 000 100

Nicaragua

371 000 100

Panama

787 000 100

Puerto Rico Trinidad and Tobago

10 000 100 1 000 100 2 524 000

18

South America Argentina Bolivia

45 000 900 100

Brazil

1 500 000 100

Chile

1 047 000 10

Colombia Falkland/Malvinas Is.

339 000 100 1 151 000

French Guyana

162 000 100

Guyana

813 880 100

Surinam

113 000 100

Uruguay

3 000 100

Venezuela

1 000 000 100 6 173 000

North America Canada

150 000 000

USA-Alaska

49 400 000

USA-S of 49° N

10 240 000 25 209 640 000

The Pacific Australia (Queensland)

15 000 100

New Zealand

150 000 30 165 000

1

Author’s estimate

19

Table 2 RELATIVE IMPORTANCE AND REGIONAL DISTRIBUTION OF TROPICAL ORGANIC SOILS Location Estimated extent Million hectares

Global %

Tropical %

All tropical and subtropical regions

35.80

8.21

100

S.E. Asia (including Papua)

20.26

4.65

56.6

Caribbean

5.67

1.30

15.8

Amazonia

1.50

0.34

4.19

African Continent (not subdivided)

4.86

1.11

13.58

South China

1.40

0.32

3.9

Other regions

2.11

0.49

5.9

2.2 The Main Occurrences The South East Asian region comprising areas surrounding the South China Sea and areas in Papua-New Guinea contain the largest expanse of peat deposits, together forming 57 percent of all known tropical peat resources. The South China Sea is a large geosynclinal basin, around the littoral of which peat has accumulated in a similar way to former geological times, when eventually coal and lignite resources were formed. The second most important area is the Amazon basin and the basins bordering the Gulf of Mexico and the Caribbean (Venezuela, Guyanas, Florida). In the wet equatorial belt of Africa a distinction can be made between the areas flanking the Gulf of Guinea, another large depressional area, and those in Central Africa where peat formation has followed recent geological uplift, rift formation and volcanism. Some of the peat areas in Central Africa are at high altitude where conditions are more like those found in temperate regions. The full extent of the areas bordering the Gulf of Guinea is not known but, because conditions are similar to those found in South East Asia, it is surmised that they are probably extensive in Gabon, Congo and Zaire.

2.3 Application of Research Peats of tropical areas when compared with those found in temperate regions are insufficiently studied. Those in Florida which are of subtropical nature, have perhaps been studied most extensively, in particular their agronomic aspects (Phillips 1985). The results of these studies are of considerable importance to tropical peats at large. Preliminary basic studies on properties of tropical peats and their agricultural potential in Indonesia are described by Polak (1941). Studies were discontinued during the Second World War and it was not until the nineteen fifties that agronomic studies restarted on tropical peats in South East Asia, mainly in Malaysia (Coulter 1957). Peat research stations were opened at Klang in Peninsular Malaysia, and at Stapok in Sarawak. Results of some 20 years of agronomic research carried out in these stations are now available to serve the region (Kanapathy and Keat 1970; Kanapathy 1976 and 1978; Kueh 1972; Tie and Kueh 1979).

20

Investigations into the more fundamental characteristics of tropical peat swamps, abandoned during the Second World War were taken up again in the early nineteen sixties, in Malaysia by Anderson (1964), and in Indonesia in the nineteen seventies (Subagyo and Driessen 1972; Driessen and Rochimah 1977). The latter studies were prematurely terminated and have not restarted. In most other tropical countries peat research is little developed, or non-existent. The behaviour of organic soils and peatswamps upon reclamation has received very little attention, even in Malaysia where research efforts were mainly concentrated on agronomic aspects. The research conducted at Klang and Stapok and that mentioned earlier in the Florida Everglades has valuable applications for other tropical regions. Once it has been established through careful classification which peat and peatswamps are comparable, it will be possible to extrapolate and apply the information elsewhere. For this reason the peat materials and their environment must be adequately characterized, defined and classified first. Much of this Bulletin is devoted to such topics in Chapters 3 and 5.

21

3. FORMATION OF PEATS 3.1 Introduction 3.2 Environmental Factors 3.3 Stages in Development 3.4 Type of Vegetation

3.1 Introduction Before starting to plan the reclamation of peatswamps it is wise to gain a proper insight into the mode of formation of the deposits and the conditions which have led to their development. The recognition of the present stage of natural peat formation is also very valuable for assessing its potential for agriculture. Discussion of the formation or genesis of peat soils is made easier by first making a distinction between the actual formation of the organic materials, and the process of their accumulation. The former is caused by biochemical processes, whereas the latter is mainly a direct function of the environmental conditions, the climate and ecosystems (peatswamps, bogs or mires) in which the peat is formed, and the climate. Organic materials only accumulate under certain conditions. For peat to form it is essential that the production of biomass (organic materials) is greater than its chemical breakdown. Not all organic materials are classed as peat. For practical reasons litter, being a special type of organic material, is excluded from our discussion. Peats are generally considered to be partly decomposed biomass (vegetation). They show a wide range in degree of decomposition. Kurbatov (1968) briefly summarizes 35 years of research into the formation of peat as follows: “The formation of peat is a relatively short biochemical process carried on under the influence of aerobic micro-organisms in the surface layers of the deposits during periods of low subsoil water. As the peat which is formed in the peat-producing layer becomes subjected to anaerobic conditions in the deeper layers of the deposit, it is preserved and shows comparatively little change with time”. According to this theory the presence of either aerobic or anaerobic conditions decides whether any biomass will accumulate and in what form. Distinction is made by Kurbatov (1968) between forest peat which is more aerated and therefore more decomposed, and peats formed under swampy conditions with strongly anaerobic conditions. In forest peat, lignin and carbohydrates appear to be completely decomposed so it generally has a low content of such organic compounds, whereas under swamp conditions peats are characterized by high contents of cutin and the presence of much unaltered lignin and cellulose (Table 3). Actually, Kurbatov’s forest peat is much the same as thick litter deposits.

22

Table 3 COMPOSITION OF SWAMP AND FOREST PEAT AS % DRY ORGANIC MATTER (source Kurbatov 1968) Swamp peat Fraction

Forest peat

Carex-swamp 30% decomposed

Reed-swamp 40% decomposed

Birchwood 55% decomposed

Bitumen

3.3

1.1

8.8

Humic acids

32.2

33.6

52.2

Hemicellulose

15.0

8.6

1.0

Cellulose

3.5

3.7

0.0

Lignins

12.9

18.6

0.0

Cutin

11.9

5.2

16.0

Not determined

21.2

29.2

22.0

This Bulletin concentrates on the development of peat in swampy conditions, since most peats in the Tropics belong to this type. Anaerobic conditions, which prevent the micro-biological activity needed for the chemical breakdown of organic materials are generally assumed to be largely responsible for the accumulation of partly decomposed biomass in the form of peat. The anaerobic conditions are created by a specific hydro-topography whether marsh, swamp, bog or mire. Properties of such hydro-topographic units depend on many environmental factors, including climate, landform, local geology and hydrology, but they all have severe toxicity others have advanced theories of high sulphur and sodium content reducing oxidation. A high sodium content is also indicated as being responsible for the development of peat in the atolls of the Maldives (Hammond 1971). Figure 1. Fundamental topo-hydrological situation for peatswamp development

3.2 Environmental Factors 3.2.1 Hydro-topography 3.2.2 Source and quality of water

The process of peat formation as a result of waterlogged conditions is called paludification. The major factors playing a role in this process are discussed below.

23

3.2.1 Hydro-topography According to Moore and Bellamy (1974) peat growth is initiated if the water balance at a site is characterized by the equation: INFLOW = OUTFLOW + RETENTION Modifying it for the climatic factor (Fig. 1) the equation reads: INFLOW + PRECIPITATION = OUTFLOW + EVAPOTRANSPIRATION + RETENTION Peat growth starts within the retention volume, peat acting as an inert body displacing its own volume of water. Peat accumulating in the initial depression is called primary peat. As peat accumulates beyond the level at which the water is drained from the basin, it no longer acts as an inert mass but as an active reservoir holding a volume of water against drainage. The development of primary peats reduces the surface retention of the reservoir. Systems of this kind are found throughout the world, except in the most arid climates. Secondary peats are those that develop beyond the confines of the basin or depression (Fig. 2). Tertiary peats are those that develop above the physical limits of groundwater, the peat itself acting as a reservoir holding a volume of water by capillary forces up above the level of the main regional groundwater-table. This reservoir forms a perched water-table fed only by precipitation. Fig. 2. Profile of a ridge raised mire (source Moore and Bellamy 1974). The height of the component copulas depends in part on the area of the mire and in part on the climate

Primary peat

Secondary peat

24

Tertiary peat

Systems producing secondary and tertiary peats are found only in climates in which retention values are high. Such conditions are frequently found in the cool wet temperate and boreal regions of Canada, Eire, Scotland and Northern Europe where peat is encroaching onto the hills forming blanket bogs. In wet equatorial and monsoon climates evapotranspiration is usually too great to cause the development of secondary and tertiary peats unless there is excessive rainfall, well distributed over the year, combined with favourable topography with a complete lack of drainage giving continuous wet conditions. Such conditions are found for example in the coastal lowlands surrounding the Sunda Flat (Malaysia/Indonesia) and in many of the other areas within the tropics listed in Tables 1 and 2. The topography is invariably basin-shaped with natural drainage being blocked by natural barriers. Common types of landscapes include: i. Saucer-shaped inner parts of islands in river deltas, which are surrounded on all sides by natural river banks or incipient levées. ii. Lagoons, which at their natural outlet are blocked by marine or riverine sediments. iii. Cut-off meander bends (oxbow lakes). iv. Fossil stream beds in braided river systems. v. Small tributary valleys blocked by mineral or organic debris at their junction with the main river. vi. Large coastal basins between major streams blocked to seaward by marine deposits (clays with mangrove vegetation, or sand dunes) and along the rivers by riverine deposits (levées). vii. Depressions in river valleys separated from the main stream by random deposition of alluvial deposits caused by frequent and erratic stream bed changes that are often related to fast and intensive deposition of high silt loads. In temperate and boreal areas many depressions now filled with peat were formed at the end of the last glaciation making these peats less than 10 000 years old. Surprisingly, most peats in the tropics are also less than 10 000 years old. Coastal peats in South East Asia are generally less than 6 000 years old (Andriesse 1974; Driessen 1977). Dating of peat samples from Sarawak by the 14C method indicates a maximum age of 4 300 B.P. (Anderson 1964). Those of Florida date back 4 400 years (Lucas 1982). This strong agreement in age has a causal relationship because melting of the ice at the beginning of the Holocene resulted in marked changes in sea level, which affected low-lying coastal regions throughout the world, changing the depositional behaviour of rivers particularly in the estuaries and deltas. The hydro-topography of tropical swamps on high ground as in central Africa (Rwanda, Burundi, and to a lesser extent in Kenya and Uganda) is largely influenced by recent volcanism which has blocked many interior valleys (Floor and Muyesu 1986). Some valleys are blocked by lava flows of very recent age and, because the lava is hard, the basins are difficult to drain. The age of these peat deposits is more related to periods of volcanic activity than to climate changes at the end of the glacial periods. Peat areas at high elevations are generally of small size because large alluvial depressions are rare.

25

The quantity and nature of the peat accumulating in a depression are very much related to depositional behaviour of the streams affecting the depression. If, for example, streams change their silt load, say seasonally, or there are other longer term fluctuations, the organic materials are contaminated with mineral deposits. Changes in the stream bed can also influence the actual site where mineral deposits accumulate. The author experienced conditions in South East Asia where deep almost pure peat is being covered by mineral deposits because of deforestation of the catchment. Deforestation causes erosion of mineral topsoil and increases the silt load of the river. It also increases the risk of flooding in downstream peat areas. The admixture of mineral deposits with peat is highly significant for potential use and requires attention when undertaking reclamation.

3.2.2 Source and quality of water Many peat researchers in the temperate regions hold the view that the mobility of the bog water is the most important factor controlling the edaphic conditions within a swamp (Kulczynski as quoted by Moore and Bellamy 1974, p.56). Before discussing influence of water flow, however, the properties of the water itself are briefly examined. The type of vegetation and the characteristics of the developing peat depends strongly on the nature of the water which is feeding the ecosystem. Traditionally, eutrophic, mesotrophic and oligotrophic conditions are distinguished. Eutrophic conditions are characterized by neutral reactions (pH of 6-7) and a high content of minerals mainly calcium carbonate. Under oligotrophic conditions there are few minerals, calcium and magnesium are particularly lacking and the pH is low. Mesotrophic conditions are intermediate. Water in a peat ecosystem can be either eutrophic, mesotrophic or oligotrophic depending on its source. But a gradual change from initial eutrophic conditions to oligotrophic conditions in the final stages of peatswamp development is very common. The sources of water and the swamps related to them can be subdivided into three groups (Kulczynski quoted by Moore and Bellamy 1974, p. 56): Rheophilous type These are swamps developing in mobile groundwater. In such cases water flows in from surrounding land and because it is enriched by cations leached from the surrounding soil the ecosystem is eutrophic and the developing organic soils are of the eutrophic type. Transitional type In this situation water no longer enters the system by surface flow but there is still some underground inflow from seepage. Amounts of incoming nutrients are therefore intermediate in quantity and the vegetation is poorer and less diverse than under eutrophic conditions. The resulting peat is mesotrophic in nature. Ombrophilous type Under these conditions water entering the system is derived only from precipitation and is therefore very low in nutrients. The water is acidified and lacks Ca, Mg and K, and consequently the vegetation is very poor giving rise to the oligotrophic organic peat soils which are extremely low in nutrients.

26

Table 4 MEAN VALUES OF THE CONCENTRATION OF MAJOR IONS IN WATERS FROM PEAT SWAMPS IN WESTERN EUROPE AND SCANDINAVIA (source Moore and Bellamy 1974) Major Ions pH Hydrological Mire

HCO 3

Cl

SO 4

Ca

Mg

Na

K

H

Total

1

Type

1

7.5 3.9

0.4

0.8

4.0

0.6

0.5

0.05

0

10.25

2

6.9 2.7

0.5

1.0

3.2

0.4

0.4

0.08

0

8.28

3

6.2 1.0

0.5

0.7

1.2

0.4

0.5

0.02

0

4.32

4

5.6 0.4

0.5

0.5

0.7

0.2

0.5

0.04

0.01

2.85

5

4.8 0.1

0.3

0.5

0.3

0.1

0.3

0.07

0.03

1.70

6

4.1 0

0.4

0.4

0.2

0.1

0.3

0.04

0.14

1.58

7

3.8 0

0.3

0.3

0.1

0.1

0.2

0.04

0.16

1.20

2

Extreme rich fen

7.7 2.3

0.2

0.4

1.8

0.9

0.2

0.02

-

Transitional fen

5.8 0.9

0.1

0.03

0.9

0.02

0.05

0.01

-

1.9

Intermediate fen

4.8 0.6

0.01

0.06

0.6

0.03

0.08

0.01

0.02

1.4

Transitional poor fen

5.5 0.1

0.04

0.04

0.1

0.03

0.06

-

-

0.38

Intermediate poor fen

4.4 0

0.03

0.05

0.06

0.03

0.08

-

0.4

0.29

Extreme poor fen

3.9 0

0.06

0.07

0.07

0.02

0.05

-

0.13

0.40

Moss

3.8 0

0.04

0.13

0.04

0.05

0.09

0.01

0.16

0.50

1 2

5.9

Types 1-7 indicate eutrophic to increasingly oligotrophic conditions - denotes less than 0.01 milli-equivalents per litre

The amount of minerals in the water has a marked effect on the species of plants and the plant associations a swamp can support. Thus where plants are rooting in the mineral subsoil and so can take up sufficient nutrients (eutrophic conditions) - plant life is rich and abundant. The initial stage of peat development (primary peat) is such a situation. At the next stage (secondary peat) inflow of nutrients diminishes because of the rising surface of the peat and the mineral subsoil gradually becomes beyond rooting depth. Deficiencies in nutrients limit the plant species able to survive. The most severe conditions of nutrient deficiency are reached at the third stage of tertiary peat formation in which the surface of the peat has risen above the surrounding land thus preventing any lateral water seepage into the upper layers of the peat which is fed by precipitation alone so the influx of nutrients is very small. At this stage vegetation has become extremely poor in species and shows retardation in growth. Table 4, based on average values of many peat bogs in western Europe, illustrates the general chemical impoverishment of the environments.

27

3.3 Stages in Development The various stages that can be distinguished in the development of peat swamps are illustrated in Figure 3 which is based on a model by Moore and Bellamy (1974) who in turn were much influenced by studies of mire ecosystems by Kulczynski. As already indicated the flow of water is extremely important for the type of peat developing, and since changes in water-flow signify the change from one stage to another we discuss the various stages in some detail. Figure 3. Model of the succession of mire types (source Moore and Bellamy 1974)

28

Stage 1 During the initial deposition of peat material in flowing water there are two alternative conditions. In the first, there is a large flow of water bringing in an amount of sediment from outside. This, in combination with a slow rate of peat formation because of strong oxygenation of the system through the large influx of water, results in the production of a heavy sinking peat, and the water flow is concentrated near the surface. In the second, there is a small water flow and less material is added from outside so, with a faster rate of peat growth, a light, floating peat is produced and the water flows below a floating mat. Stage 2 The accumulation of peat tends to canalize the main flow of water within the basin, leaving some areas (hatched in Fig. 3) which are subjected to the effects of moving groundwater during periods of excessive flow only. Again two alternatives are recognized: first, where the whole peat mass is inundated, and second where the peat mass is not inundated and is floating. Stage 3 The continued vertical and horizontal growth of peat causes the largest part of the basin to be beyond the influence of inflow. Water supply is mainly restricted to rain falling directly on the swamp surface with some seepage from surrounding areas. Only those areas immediately lying along the main drainage tracts within the swamp may show a slow continuous flow. Stage 4 Continuing peat growth leaves most of the swamp unaffected by moving water but inundation will occur when the water-table in the basin rises as a result of heavy rainfall. Stage 5 The peat surface has risen so it is no longer affected by seasonal fluctuations of the groundwater. The dome-shaped peat surface possesses its own perched water-table fed by rainwater. The stages (1-3) in which the system is fed to some degree by water from the surrounding areas gives rise to so-called topogenous peats. Whereas the late stages (4-5) in which almost all the minerals available are re-cycled within the ecosystem, give rise to ombrogenous peats. Although this model is based on numerous studies in western Europe and other temperate regions, it can be applied to tropical regions as is shown in schematic form in Figure 4 by an example of the successive stages in the development of deep peatswamps in coastal areas (Andriesse 1974). This is based on field information obtained from surveys in the Sarawak Lowlands, Malaysia, by Anderson (1964) and the author. Here too the development of primary, secondary and tertiary peats can be recognized, and a division can be made into topogenous and ombrogenous stages. Anderson (1964) also provides evidence of former islands of low elevation now completely covered by tertiary peat deposits. Figure 4 illustrates that in a strong depositional environment, as is often found in a monsoonal or semi-arid climate, the evenly spread accumulating mineral deposits will slowly raise the floor of the basin and prevent complete blockage of drainage. In such cases peat development is either absent or found only in small depressions when favourable hydro-topographic conditions are present. 29

Many peat deposits in tropical areas show in cross-section the various stages described. The bottom layers are rich in plant species and are in general richer in plant nutrients than the overlying layers. There is generally a gradual impoverishment in the mineral content of the peat, particularly in the major elements, calcium, magnesium, potassium and phosphorus. Depth of peat is therefore an important indicator of fertility. The type of peat, whether topogenous or ombrogenous, gives clues to the fertility to be expected.

3.4 Type of Vegetation Peatswamps can have very contrasting types of flora. The current vegetation, which is not necessarily the same as that of the past, generally reflects the age or stage of development of the peat and the climate. A vertical cross-section across a peatswamp reveals the succession of plant associations which must be regarded as the original materials of the peat. These layers from top to bottom could, for example, show the following succession: trees; shrubs; grassy perennials (sedge grass, saw-grass) forming a dense mat; large perennials protruding from shallow water and possibly still rooting in underlying mineral soils; rooted aquatics with floating leaves; floating aquatic plants, algae and plankton. Figure 4. Stages in formation of peatswamps in South East Asia (source Andriesse 1974) The vegetation layers commonly follow the stages in development recognized in the previous section. During Stage 1 (Fig. 3) algae, weeds and mineral deposits are produced. In successive stages as organic residues accumulate, conditions become more favourable for the growth of reeds, sedges and other perennials which retard water flow further. The diminishing influx of nutrients available for vegetative growth leads to impoverishment of the system and in the later stages of development only the more acid-loving plants are able to survive. The decomposing biomass produces inorganic and organic acids which tend to accumulate in the ecosystem as the neutralizing effect of calcium carbonate in the incoming water from surrounding land is no longer effective. Examples of acid vegetation include specific plant associations dominated by heath, sphagnum moss and many other acidophile plants. There are numerous papers on the ecological and botanical aspects of organic soils and botanists have developed procedures to identify former vegetation associations by microtome analyses of peat fibres and pollen analysis. It is beyond the scope of this Bulletin to provide detailed information on every possible vegetation type. It is well, however, to realize that present vegetation cover can be a sound indicator of the development stage of the peatswamp and that the vegetation of the various underlying peat layers can give major clues to the mode of peat formation and its relative richness of plant nutrients. In classifying peat, use is often made of the nature of original material, this being either moss-like (Sphagnum), grass-like (sedges, saw-grass, papyrus), reeds, bush or forest. For reclamation purposes such distinctions are relevant and they are dealt with under the appropriate heading in Chapter 4. In conclusion, notes are given on the rate of accumulation of peats. First there is no essential difference between the mode of formation of peatswamps and peats in tropical and temperate areas. In both cases climate plays a decisive role in the dynamics of the processes involved. Because of climate, the rate of build-up of barriers by silt in rivers is greatest in the tropics. Also, the much larger amounts of water generally passing through the tropical systems (rainfall of 4 000 mm compared with say 700 mm in a temperate region) and the seasonal differences in temperature regimes considerably influence water regime. 30

Apart from the difference in dynamic processes, the kinetics of energy influx and its dissipation are vastly different in the tropics when compared with temperate zones. This has a large effect on the rate of accumulation of peat because biomass production is many times greater than that in temperate regions. On the other hand oxidation and decomposition are also much enhanced in the tropics by higher temperatures. There are numerous studies on rates of peat accumulation and there appear to be many factors involved. Lucas (1982) in a review of a number of studies, indicates that it generally requires between 600 and 2 400 years for 1 m of peat to accumulate with an average of 1 500 years. These studies are mainly related to boreal and temperate climates and indicate varied conditions. From studies by Anderson (1964) on the forest peat of Sarawak it can be calculated that the deepest layers of peat (4 300 years old) accumulated at a rate of 1 m in 214 years, those 3 900 years old accumulated at a rate of 1 m in 333 years, but those laid down in the last 2 300 years took 455 years for 1 m to accumulate. These figures indicate that peat in tropical climates accumulates at least 3 times as fast as in temperate areas. They also show that, as in temperate regions, the rate of accumulation is related to the stage in development. This is logical since, with increasing impoverishment of the ecosystem, biomass accumulation will be slowed down, and as a consequence also peat accumulation. Tropical peats in South East Asia appear to be mainly of the forest type. The vertical succession in the coastal lowlands (Anderson 1964) is commonly characterized by mangrove species at first (Stage 1) followed by transitional, brackish water communities in later stages. These change to true freshwater swamp communities which in turn are finally replaced by the a poor Shorea albida monostand on the ombrogenous raised peat domes. Although forest peat is the rule rather than the exception in the coastal lands of the wet tropical belt this is not necessarily always so. As always the type of peat depends on the stage of development, site characteristics and climate. The dominance of forest-type peats in the tropical lowlands tends to be replaced by a Cyperacea type of vegetation (saw-grass, papyrus) when passing to a subtropical climate, whereas sedges and reeds develop almost anywhere depending on the hydrotopography of the site. Peats at high elevations in the tropics, say at over 2 000 m, are generally of a grassy and mossy nature. In Burundi/Rwanda, peat contains Sphagnum and attains characteristics of the peats of temperate regions.

31

4. THE MAIN CHARACTERISTICS OF TROPICAL PEATS 4.1 Introduction 4.2 Physical Properties of Organic Materials 4.3 Chemical Properties of Peat Materials 4.4 Biological Activity 4.5 Characteristics of the Peatswamps

4.1 Introduction Peat materials can be characterized in various ways depending on the purpose for which they are being described. For example, evaluation of peat materials as a source of energy requires emphasis on different characteristics than those needed to assess its agricultural potential. Reclamation of peat requires knowledge of different properties, including those that put emphasis on the nature of the peatswamps rather than the peat material itself. Keeping in mind the many purposes for which data on peat and peatswamps is required, the most relevant characteristics are listed in Tables 5 and 6. Table 5 concentrates on the physical and chemical characteristics of the peat materials; Table 6 is concerned with the topo-hydrological conditions of the peatswamps. Table 5 MAIN CHARACTERISTICS OF ORGANIC SOIL MATERIALS OF RELEVANCE FOR AGRICULTURAL DEVELOPMENT Physical properties Moisture relationships

Chemical properties Composition

water retention

organic compounds

available water

elemental

hydraulic conductivity water holding capacity Bulk density

Acidity Exchange characteristic

non-specific

cation exchange capacity

specific

exchangeable cations

Porosity

Organic carbon status

Texture (loss on ignition)

Nitrogen status

Irreversible drying

Phosphorus status

Swelling and shrinking

Free lime (CaCO 3 ) Sulphur status Trace elements with emphasis on Cu

32

Table 6 MAIN CHARACTERISTICS OF PEATSWAMPS Geomorphology

Hydrology

Topographic situation

Water sources

Surface configuration

Quality of water

Elevation of surface

Position of natural drainage channels

Elevation of underlying mineral soil

In the discussion below we use data on tropical peat resources whenever it is available, but in the absence of adequate data from the tropics we have drawn on information from temperate regions. As indicated earlier one of the common causes of reclamation failure is the lack of recognition of the difference between the properties of mineral and organic soils. This extends to the use of analytical procedures. For this reason much attention is given in the following sections to the analytical methods used to measure characteristics and the differences between parameters. These are frequently confused in the literature and elsewhere leading to misinterpretation and mismanagement. It also seems desirable to pay some attention to management early in the text so the fundamental issues in characterizing peats in relation to management are properly recognized.

4.2 Physical Properties of Organic Materials 4.2.1 General 4.2.2 Moisture relationships 4.2.3 Bulk density 4.2.4 Porosity 4.2.5 Texture and loss on ignition 4.2.6 Swelling and shrinking 4.2.7 Irreversible drying 4.2.8 Physico-chemical properties

4.2.1 General The physical properties of organic soils are of particular relevance to water management purposes and for this reason they are discussed at some length. Organic soil materials consist of four components, mineral material, organic material, water and air. The characterization of the physical properties of organic materials is made difficult by the changes in the proportions of the four components as a result of reclamation. There is another complication. Traditionally the study of physical properties was more the domain of soil mechanics and soil engineering than of soil chemistry. The former disciplines express characteristics of materials on a volume basis, whereas chemists commonly use weight ratios. There is a tendency at present to use volume ratios, because it is more practical to work with them. It is beyond the scope of this Bulletin, however, to discuss weight/volume relationships in organic soils in much detail, and the reader is referred to the guidelines given by Skaven-Haug (1972), who has worked out the mathematical relationship between the different expressions for water content and the general expressions for volumetric relationships for the four components of organic materials. A synopsis is given in Appendix 2. The characteristics are discussed in a more or less logical order. Because of the strong interdependence of the various physical properties, it is difficult to discuss each individual characteristic independently. It is thus necessary to make frequent cross-reference. 33

4.2.2 Moisture relationships Information on the water content of organic soils is extremely important in reclamation. In particular it is needed for the design of efficient drainage layouts. There are various methods of determining the water content of organic soils. Each of them gives variable results in different kinds of organic soils, often with a different order of magnitude. Farnham and Finney (1965) compare three different methods (Table 7) on three different kinds of organic materials fibric, mesic and sapric types (Chapter 5). Table 7 THE COMPARATIVE WATER ABSORBING AND WATER RETAINING CAPACITIES OF THREE ORGANIC SOIL HORIZONS (source Feustal and Byers 1936, as quoted by Farnham and Finney 1965) Kind of organic soil horizon Fibric Maximum moisture holding capacity %

Mesic

Sapric

1057

374

289

Moisture equivalent %

166

112

110

Water required to saturate 100 cm of dry material (g)

101

91

99

Water required for moisture equivalent of 100 cm3 of dry material (g)

16

27

38

Weight of 100 cm3 of dry material (g)

11

27

39

In Table 7, the maximum moisture or water holding capacity is the amount of water the soil retains against gravity, based on the oven-dry weight at 105°C. It can also be defined as the quantity of water held by a soil as a function of the height of the soil above the surface. The moisture equivalent (Table 7) is determined by placing the soil in a perforated box and centrifuging it at a force of 1 000 times gravity for 40 minutes. The third method (Table 7) measures the amount of water required to saturate a standard volume of dry peat (100 cm3) and thereafter measure its moisture equivalent. Table 7 shows that there are great differences in the results of the various methods, but irrespective of the method, water contents in fibric materials always appear to be appreciably higher than in sapric materials. The degree of decomposition and also botanical origin are clearly an influence. A further method preferred by soil scientists is the measurement of water retention values using pressure plate and pressure membrane apparatus. This method is superior to the others because it shows great differences in water release characteristics between the various organic materials (Table 8), and it is therefore discussed in detail below in the sections on water retention and available water.

34

Table 8 THE WATER RETENTION PROPERTIES OF THREE DIFFERENT ORGANIC SOILS (source Dyal 1960, as quoted by Farnham and Finney 1965) Kind of organic soil horizon Fibric Water retention 1/10 bar (%)

1

Mesic

Sapric

570

193

163

Water retention 1/3 bar (%)

378

150

144

Water retention 15 bar (%)

67

84

100

1

Determined by pressure plate and pressure membrane procedure based on oven-dry weight

Water retention Water retention values are particularly important in the management of organic soils. Table 8 shows clear differences depending on the degree of decomposition. There is much confusion about the moisture retention values being expressed in several ways: as a percent by volume; as percent of the over-dry weight; or as the percent of the wet weight. Boelter and Blake (1964) show that not only is it necessary to express the water contents of organic soils on a volume basis because of their varied bulk densities, but because of the volume reduction occurring on drying, water contents must also be expressed on a wet volume basis as taken in the field. For example, the water content of fibric horizons at all suctions, when expressed on an oven-dry basis, are greater than those of mesic horizons. These in turn are greater than those of sapric materials. Mineral soil materials usually contain considerably less water than organic materials at all suctions. However, using the same water contents, expressed on a volume basis (the amount of water lost expressed as the volume of water per unit volume of soil in bulk) fibric horizons appear to contain least and sapric materials most of all organic materials. A mineral soil would probably contain a volume of water of the same order of magnitude as the peats at the higher tensions. This feature is well illustrated by comparing Table 8 with Figure 5. This figure shows that the undecomposed sphagnum moss (fibric material) has the lowest water retention values, because the latter are expressed on a percent volume basis, whereas in Table 8 values are highest for this type of peat at low tensions, because water content is expressed on an oven-dry weight basis. The large variation in water retention between the materials is a function of the porosity and hydraulic conductivity. Coarse fibric materials have large pores whereas the most-decomposed sapric material has relatively small pores but not necessarily a smaller pore volume. Another observation which must be made is that the pF curves shown in Figure 5 are remarkably flat, a characteristic which appears to be common in peat soils particularly in the range 0.04 to 0.33 bar suction. Driessen and Rochimah (1977) made a similar observation on pF curves of coastal lowland peat from Borneo which had 79-91 percent by volume at a suction of 0.01 bar, 75-89 percent by volume at 0.1 bar and 71-85 percent by volume at 0.33 bar. Fibric peats apparently lose much of their retained water at low suctions. Water appears to be increasingly held as the degree of decomposition increases.

35

Figure 5. Water retention curves for several northern Minnesota peat materials (source Lucas 1982) Plate 1. Vegetable growing on beds, by Japanese settlers on 1.5 m thick peat in Brazil, practising sprinkler irrigation to prevent desiccation. Note the original primary forest in the background

Available water Agricultural management requires information on the difference between the quantity of water retained at field capacity and the water retained at the permanent wilting point. Both values are measured quantitatively by the mentioned pressure plate and pressure membrane method (moisture retention or pF analysis), field capacity being the amount of water held at a suction of 0.33 bar or at a pF of 2.2 (the pF being the logarithm of the height of water in centimetres). Wilting point is the moisture content at 15 bar section or pF 4.2. Although theoretically the difference between pF 2.2 (0.33 bar) and pF 4.2 (15 bar) should give an indication of the amount of water available to the plant, in practice under field conditions, the quantity of water in organic soils available to the plant appears to be much less. For management purposes and in terms of water available to plants, two properties differentiate mineral and organic soils. First the volume of solid particles is much less in organic soils than in mineral soils and second the amount of water retained at very low tensions is much greater for organic soils than for mineral soils. Experience in Florida shows that productivity decreases markedly as the store of available water falls below 30 percent of the maximum available water (Lucas 1982). The tension at this moisture content is about 5 bar. This observation is worth checking under tropical conditions where drought conditions are more severe. The author notices in Brazil that Japanese immigrants used sprinkler irrigation for vegetable growing to keep the surface layer moist in the dry season. This prevents the start of irreversible drying and partly rectifies deficiency in moisture, although the water-table was only at 30 cm depth. This clearly indicates, however, that water availability and capillary action in peat soils and mineral soils are not directly comparable. Peat soils behave more like the very lighttextured soils than like heavy-textured ones. Much fieldwork still needs to be done on the availability of water held at low tensions and the nature of the capillary fringe above the watertable.

Hydraulic conductivity The rate of movement of water through the soil is highly relevant to drainage problems. It is controlled by several factors. The type of peat, degree of decomposition and bulk density influence hydraulic conductivity and they provide a good basis for its assessment (Boelter 1974). Sapric horizons of some Canadian peats (Irwin 1968, quoted by Tie and Kueh 1979) have very low permeability in the order of 0.36 to 0.036 cm/h, which is less than that of many fine textured soils, but Soepraptohardjo and Driessen (1976) report rapid horizontal hydraulic conductivity but slow vertical conductivity for some peats in Indonesia. Lucas (1982) indicates that, in general, fibrous peats have moderate rates of water movement while decomposed and herbaceous peats often have low values. This corroborates the findings of Irwin. Rates less than 0.36 cm/h are too slow for successful agricultural development. Laboratory studies on Holland Marsh mucks in Ontario State, USA, give hydraulic conductivity values of 22, 18 and 4 cm/h for depths of 0-15, 15-30 and 30-45 cm respectively. Florida peat soils (12-21 cm depth) were found to have a hydraulic conductivity ranging from 29-67 cm/h depending on soil series. Horizontal hydraulic conductivity rates can be faster than vertical rates if the profile has a decomposed subsoil, but Clayton et al. (1942) conclude in a study of water control of the Florida Everglades, that vertical movement of water is greater than horizontal movement and this could be related to orientation of the saw-grass roots which were generally vertical. 36

Apart from the sources mentioned, there is little other data from the tropics. It is, however, clear that for a proper estimate of the hydraulic conductivity many factors must be studied and the influence of each on water movement evaluated. Fibric materials in tropical peats commonly exhibit high hydraulic conductivity, which gradually diminishes as the peats decompose. Decreasing pore space and higher water retention in developing sapric materials affect the hydraulic conductivity considerably. The fact that gradual changes in hydraulic conductivity can be expected in decomposing peat following reclamation must be borne in mind.

Water holding capacity The amount of water held by a soil is partly a function of the height above the water-table. There are several methods to measure this quality. The American Society for Testing and Materials (ASTM) uses a procedure that measures the moisture held by a 22 cm high column; Finnish scientists use a 10 cm2 tube holding a column of peat. Tube and soil are immersed in water until they reach constant weight. For dry peats, this may require several days. The tube is then placed in a vertical position for two hours to allow excess water to drain. Other workers use metal containers with 5 X 5 X 2 cm dimensions and a metal screen on the bottom. After saturation the containers are placed in a Bell jar and the soil allowed to drain. Water holding capacities measured this way are greater than those obtained by the ASTM and Finnish methods (Lucas 1982). The difference in weight between the wet and the oven-dry soil (105°C) is the moisture held, so the values are expressed on a dry-weight basis. Water holding capacity values show marked differences. The weight of water held in fibric horizons may be as much as 20 times the weight of the solid-particles, whereas that held in cultivated sapric horizons contain less than twice the weight. If the water holding capacity is expressed on a volume basis these differences are much less apparent. This is clearly shown in Table 9. Thus, the difference between values of water holding capacity expressed on an oven-dry weight basis (water content percent dry basis in Table 9) can be used to distinguish between stages in decomposition and peat types. There is not much information available on water holding capacity of typical tropical peats. Tay (1969) mentions values for Malaysian coastal peats which are usually woody and fibric at depth, of 15 to 30 times their own weight. Ehrencron, quoted by Andriesse (1974), determined the water holding capacity of two West Borneo peats as being 322 and 275 percent, values which are considered low and which are probably related to cultivated peat with sapric characteristics. Table 9 DRY WEIGHT AND WATER CONTENT OF SATURATED PEATS (source Lucas 1982) Peat types Sphagnum Fibrous reed-sedge Decomposed reed-sedge Peat humus Peat weight g/l 1

88

160

240

320

930

890

835

780

1018

1050

1075

1100

Water content % wet basis

91

85

78

71

Water content % dry basis

970

554

346

242

Water content g/l Total weight g/l

1

1

1

g/l indicates grams per litre

37

4.2.3 Bulk density Bulk density is perhaps the most important intrinsic characteristic of peat because many other properties are closely related to it. For this reason it is used as a parameter for classifying peat at high categorical levels (Chapter 5). Bulk density however depends on the amount of compaction, the botanical composition of the materials, their degree of decomposition, and the mineral and moisture contents at the time of sampling. The actual method of determining bulk density is an important consideration in evaluating data. The bulk density of an organic soil is the weight of a given volume of soil usually expressed on a dry weight basis in grams per cubic centimetre. Values range from 0.05 g/cm3 in very fibric, undecomposed materials to less than 0.5 g/cm3 in well decomposed materials. If expressed on a wet volume basis, which is the mass per unit wet bulk volume of soil that has been dried to constant weight at 105°C (in other words the weight of 100 cubic centimetres of dry material in grams) the values have a totally different meaning. It is therefore important to note which method has been used. To complicate the matter further other researchers report bulk density in terms of mass per unit volume but after a standard packing procedure and the values obtained are of greater magnitude than the first mentioned. There is little point in reporting all bulk density values known for tropical peats, because type of peat and degree of decomposition play an important part in the differences noted. For this reason only some general indications are given. Andriesse (1974) reports mean bulk densities of 0.12 and 0.09 g/cm3 for Sarawak (Malaysia) peat. Driessen and Rochimah (1976) corroborate these findings and indicate that fibric tropical peats in Indonesia commonly have bulk densities of less than 0.1 g/cm3 and those of the well decomposed sapric peats have values greater than 0.2 g/cm3. Tie and Kueh (1979) specifically mention the bulk density of a well-decomposed sapric peat at the Stapok Peat Research Station in Sarawak. This peat, with a loss of ignition of 95 percent, has bulk densities of 0.15 and 0.13 g/cm3 at depths of 015 and 15-30 cm respectively. The bulk density values reported for the uncultivated Florida peats are within this range. Cultivated soils around the Agricultural Research and Education Centre, Belle Glade, however, have topsoils (0-15 cm) with a bulk density of 0.35 g/cm3 and subsoil (45-60 cm) densities of 0.18 g/cm3. These higher densities are no doubt caused by cultivation and compaction of the surface layers upon drainage. This appears to be a general feature of most tropical peats under natural conditions as surface layers are generally more sapric than subsurface layers. This is the effect of climate, height of water-fable and oxidation. Bulk density measurements are of practical importance in interpreting soil analytical data particularly those indicating fertility levels. Chemical data are commonly expressed as parts per million (ppm) or percentage on a 100 g dry-soil basis. The comparison between the fertility level of a mineral soil with bulk density of 1.5 g/cm3 with the fertility level of an organic soil with a bulk density of 0.1 g/cm3 is not realistic unless the great difference in bulk densities is taken into account. Otherwise it would indicate a level 15 times its true value for the organic soil. Analytical values for organic soils must be recalculated on a weight per volume basis, using bulk density as a correction factor. Some research workers determine the specific density (particle density) which indicates the true densities of the solid peat material. Its measurement is complicated and tedious and is traditionally done by a picnometer. However, there are other direct and indirect methods (Skaven-Haug 1972). Its value is influenced by the amount of mineral matter present in the organic materials. Driessen and Rochimah (1976) quote specific density values ranging from 1.26 g/cm3 to 1.80 g/cm3 for peats in general. They determined values in Indonesia of 1.4 g/cm3 for the lowland peats of an ombrogenous and oligotrophic nature. Specific density values do not have a direct practical application. Care should be taken to avoid confusion with values for bulk density. 38

4.2.4 Porosity Total pore space (TPS) largely determines the water retention. As indicated earlier fibric horizons have a high rate of water movement because of the large pores usually present. Large pores collapse on progressive decomposition and total pore space also decreases. It is possible to determine total porosity by using bulk density and specific density values in the following formula: TPS in 100 cc of soil = [100 (SD - BD)] ÷ SD in which SD is specific bulk density and BD non-specific bulk density. Driessen and Rochimah (1976) calculated total pore space using these parameters for tropical lowland peats in Indonesia and concluded that the total porosity depends primarily on the bulk density of the material (Table 10). Boelter (1974) indicates that fibric peats in their normal state commonly have a total porosity of 90 percent by volume, whereas sapric materials commonly have less than 85 percent pores. The findings of Driessen and Rochimah appear to confirm these values. It is important to realize that on drainage the porosity changes drastically. Table 10 CALCULATED TOTAL PORE SPACE (% vol.) FOR TROPICAL LOWLAND PEATS IN INDONESIA (source Driessen and Rochimah 1976) SD (g/cm3) 1.30

1.40

1.50

% volume

% volume

% volume

0.10

92.3

92.9

93.3

0.15

88.5

89.3

90.0

0.20

84.6

85.7

86.7

0.25

80.8

82.1

83.3

BD (g/cm3)

4.2.5 Texture and loss on ignition The texture of organic materials is determined on both the organic and the mineral parts of the soil. The method of determination of size fractions of the organic part of the material is given in Chapter 5, while the texture of the mineral part is determined by the usual granulometric method after removal of the organic material. A quick method to establish the amount of mineral matter in an organic soil is by loss on ignition. In this method the sample is incinerated after oven-drying at a temperature of ±800°C (some, for example Kanapathy (1976), use 480°C). Not all of the loss on ignition is caused by the oxidation of organic matter. Mineral material after drying to 105°C contains chemically- and physically-bound water which dissipates upon further heating. Also organic materials contain a small amount of chemically combined mineral matter. Skaven-Haug (1972) quoting various sources indicates that slightly transformed, presumably pure sphagnum peat has an ash content between one and two percent. For tropical peats consisting of pure organic materials a presumed ash percentage of one percent seems reasonable. In the case of mineral matter weight losses on heating due to loss of water and in some cases by volatilization of calcium carbonate, are more difficult to assess. Pure mineral matter should give a weight loss of less than one percent but this depends very much on the nature of the mineral material.

39

Skaven-Haug (1972) indicates values of 0.4-1.3 percent for sand and silt and values of 3.9-6.0 percent for very fine clay material. When a sample contains lime, losses due to generation of carbon dioxide amount to approximately half the weight of the lime. For example, an approximate lime content of 3-5 percent gave ignition losses of 1.5-2.5 percent. After the corrections mentioned above, the loss on ignition is an important practical parameter. With sufficient samples it can be used to estimate the amount and distribution of mineral matter in a peat bog both vertically and laterally so that behaviour upon drainage can be predicted. The nature of the mineral component in organic soils has a bearing on soil fertility and agricultural potential and it must therefore be analysed. In addition, subsidence plays an important role during reclamation (Chapter 7), and is closely related to the amount and nature of the mineral matter in the organic material.

4.2.6 Swelling and shrinking Most organic soils shrink when dried but swell when re-wetted, unless they are dried to a threshold value beyond which irreversible drying occurs (section 4.2.7). Shrinkage calculated as a percentage of the original volume ranges from 90 percent for aquatic peats to 40 percent for fibric peats. Canadian peats, commonly show the greatest shrinkage where the bulk densities are lowest and the content of gelatinous materials highest (Maas, as quoted by Lucas 1982). This is probably also true for lowland coastal peats in Indonesia as is indicated in Table 11. Organic soils appear to become less affected by drying after they have been cultivated for some time. This is partly related to the increased decomposition and gradual change from a fibric to a more sapric nature. The wood content of the peat influences shrinkage as the wood acts as a stable skeleton reducing shrinkage of the whole. This was so in Florida where moss peats and most fibrous peats shrink the least and sedimentary plastic mucks shrink the most. In all probability the amount of mineral matter in organic soil and the nature of the decomposed organic materials influence shrinkage most. This explains the large differences reported in Florida where saw-grass peat shrank 20-25 percent, semi-aquatic mucks 10-15 percent, woody mucks 30-50 percent and mangrove mucks about 4050 percent (Lucas 1982). Table 11 THE EFFECT OF DRYING ON FOUR SURFACE SOILS FROM A SEQUENCE NEAR TAMBAN, CENTRAL KALIMANTAN, INDONESIA (source Driessen and Suhardjo 1976) Profile

Cultivation period (years)

Field bulk density

Bulk density after drying

Shrinkage % volume

Field moisture content % weight

Re-moistened moisture content % of FMC

PD 11

6

0.28

0.86

67

301

28

PD 12

3

0.23

0.70

67

354

29

PD 13

1

0.12

0.60

80

705

15

PD 14

0

0.13

0.85

85

557

10

40

4.2.7 Irreversible drying Irreversible drying occurs after periods of intensive drying and is typical of many peat soils. Surface layers of organic materials in many reclaimed and drained peatswamps exhibit this behaviour. After exposure to the sun, the materials become rather like coffee grounds, and are very difficult to re-wet. This may cause severe drought stress in shallow rooting crops. There are several explanations of the cause of the property. Coulter (1957) attributes the hydrophobic nature of dried peat to the presence of a resinous coating which presumably forms upon drying. He suggests this coating prevents the reabsorption of water. There is some doubt about this. For example, Driessen and Rochimah (1977) did not find such coatings in Indonesian peats and the author has never seen them. Lucas (1982), quoting Puustjarvi and Robertson, indicates that acid, humified peats exhibit the greatest resistence to re-wetting because of their carboxyl and phenolic hydroxyl groups, and high lignin content. Consistent with this theory is the observation that changes in sphagnum peats are usually small because they are low in lignins, but that the condition occurs very markedly in vascular and hypnaceous peats with large pores. Most tropical peats belong to the latter group. Re-wetting resistence has also been explained as due to adsorbed air films and iron coating around the organic particles. Resistence to re-wetting also appears to be related to bulk density. Thus irreversible drying is marked in organic soils with low bulk density but those with high bulk densities are comparatively easy to re-wet. Several investigators report complete re-wetting where soils have high bulk densities (greater than say 4.2 g/cm3). Peats reaching the stage of irreversible drying show a marked loss of water holding capacity which can be as much as 40-75 percent in the case of peats in the USA.

4.2.8 Physico-chemical properties The discussion on physical properties is perhaps best closed by summarizing some of the fundamental peat research findings on physico-chemical properties arrived at by the USSR Peat Institutes. The need to develop new technological processes for various industrial uses of peat has spurred USSR research workers to investigate moisture characteristics, and the physico-chemical structural and rheological properties of peat materials. This has produced much information on the basic micro-structures and molecular composition of peats and their changes during production, processing and dehydration. Such information can also provide clues to the behaviour of peat materials when reclaimed. It also sheds light on other physical and chemical properties which are more readily explained using this background information. Volarovich and Churaev (1968) describe peat as a complex, heterogeneous, poly-dispersed system consisting of both true solutions of low and high molecular weight, hydrophobic sols and hydrophilic semi-colloids in a dynamic state of dispersion at equilibrium. The structure of the peat colloids is determined by the chemical composition of the compounds formed during the decomposition of vegetable matter, whereas the coarse-dispersed fraction is composed of plant remains in the form of insoluble and high co-polymers of cellular tissues. Peats can be divided into two kinds: High moor peat This, comparable to most dome-shaped lowland tropical peats of ombrogenous oligotrophic nature, has a large hydrophilic humic material content (humic acids and hemicellulose). An increasing degree of decomposition results in an increase in hydrophobic components. This explains the stronger irreversible drying in sapric materials than in fibric materials.

41

Low moor peat This peat of eutrophic nature is uncommon in the tropics and appears to have a smaller content of hydrophilic materials. The colloid fraction mainly consists of humates of polyvalent metals forming compact coagulated aggregates. The behaviour of colloids in peat is strongly determined by the kind of adsorbed cations, which depend on salt content and acidity which in turn depend on the nature of the water and the mineral supply. In high moor peats, where water supply is maintained by precipitation adsorbed metal cations are less important. The hydrophilic nature of high moor peat is reflected by the large content of bound water which is directly related to the content of hydrophilic colloids, the maximum values of both occurring at a degree of decomposition of 20 to 30 percent. Further decomposition results in an increase in hydrophobic material as the bitumen content increases. Investigations by Rebinder, quoted by Volarovich and Churaev (1968) indicate that water in peat can be divided into three categories: physically and chemically bound water; capillary and film water; and immobilized water. Physically and chemically bound water This is absorbed at the solid-liquid interface by the active groups of high molecular weight compounds. The energy of adsorption by Van der Waals forces, or hydrogen bonding, ranges from 0.1-0.3 up to 5-10 kcal/mol. Contents range from 40-70 percent of the total water in raw peat of which 10-15 percent is very tightly bound, possessing bond energies greater than 1 kcal/mol. Because this physically and chemically bound water is mainly tied to compounds of high molecular weight, there is a good correlation between the amount of bound water and the content of hydrophilic material. This is not so in low moor peat where the hydrophilic characteristics depend also on the composition of the adsorbed cations and the pH. Physically and chemically bound water also includes water held by osmosis. This water is responsible for the swelling of hydrophilic colloids which have structural lattices forming partitions permeable to water but impermeable to the larger molecules of compounds of high molecular weight. Capillary and film water This is retained by forces of negative and wedge pressure at the air-water interface. The bond of energy is <0.2-0.3 kcal/mol. If there is no air in the soil, capillary and film water becomes free water without a surplus bond energy. Immobilized water This is held in peat by purely mechanical forces and its bond energy is negligible. It comprises intracellular water, entrained on cell structures and the water in closed pores. Dispersion, compression or destruction of the structure may result in conversion of this water to free water. The bound water in peat consists mainly of capillary and immobilized water. Raw peat holds 200500 percent immobilized water and up to 250-400 percent capillary water. When the peat is little decomposed, intracellular water forms the main portion of the immobilized water. Water entrained by the colloids increases upon decomposition. The total amount of immobilized water becomes constant when the peat is 30-40 percent decomposed. As decomposition continues the amount of capillary water decreases, because of the destruction of plant remains and increasing compaction.

42

In highly dispersed systems such as peat, moisture transfer can be considerably influenced by colloidal-chemical processes and by surface phenomena at the interfaces. It is therefore not only a hydro-mechanical but also a physico-chemical problem. Experiments have indicated that changes in peat infiltration coefficients are associated with swelling and colloidal-chemical changes which occur simultaneously. Increasing pH and hydrophilic nature of the peat causes development of the gel structure, arresting infiltration. Reduction of pH and compact coagulation of the colloids results in increased permeability. All these factors cause deviations from Darcy’s Law. The phenomenon of moisture conductivity in peat is no less complex. Investigations into drying indicate that the first drying stage is characterized by the removal of free water and of water from large pores. On further drying, the forces of capillary contraction increase and weakly bound intracellular and immobilized water is squeezed out. The transfer and removal of moisture in microcapillaries brings about a change in the transport mechanism and a reduction in the drying rate. This change corresponds to the first critical point of a drying curve. After removal of the mechanically bound water, the rate of drying is reduced still further. This is followed by the removal of physico-chemically bound water. This stage coincides with a second critical point. At such a moisture content, highly dispersed samples show a change in the rate of shrinkage due to increasing forces of molecular interaction with the removal of water and with convergence of the particles. The removal of moisture appears to follow a strict sequence determined by the bond energies. Resulting changes influence the strength of the peat. Thus at moisture content greater than 150-200 percent when bonding is related mainly to capillary action, the strengths of blocks of peat from high and low moor are approximately equal and depend on the pore volume. The maximum strength of the peat is achieved at a moisture content approaching that of the physicochemically bound water. With further dehydration, irreversible changes in high molecular compounds take place and the peat becomes more fragile. This explains the coffee grounds and powdery peat structure formed in surface layers of reclaimed peat soils as a result of drying in the sun (Section 4.2.7).

4.3 Chemical Properties of Peat Materials 4.3.1 Introduction 4.3.2 Composition 4.3.3 Acidity 4.3.4 Exchange characteristics 4.3.5 Organic carbon 4.3.6 Nitrogen 4.3.7 Phosphorus 4.3.8 Free lime (CaCO 3 ) 4.3.9 Sulphur 4.3.10 Trace elements

4.3.1 Introduction In the past the chemical characterization of peat materials concentrated more on the compound organic constituents and the elemental composition, than on derived chemical properties such as exchange characteristics. This is because the methods were developed in the traditional peat mining countries in temperate regions. They were more interested in peat as a source of energy than as a medium for plant growth. More recently, industrial use of peat has instigated a new interest in its chemical properties, the study of which is presently being helped by modern analytical techniques. In this Bulletin we only concentrate on basic chemical composition when it is of importance for a better understanding. Attention is mainly focused on the important derived chemical properties affecting agricultural potential, agricultural management and the behaviour of peats upon reclamation. 43

4.3.2 Composition Organic compounds The chemical composition of peat materials is predominantly influenced by the parent vegetation, the degree of decomposition and the original chemical environment. Peat science traditionally distinguishes the following main organic constituents grouped into five fractions which can be determined separately: a. Water soluble compounds. b. Ether and alcohol soluble materials. c. Cellulose and hemicellulose. It is possible to separate cellulose from hemicellulose by extracting the residual sample with 2 percent HCl at 100°C for five hours under a reflux condenser. The amount of hemicellulose is estimated by multiplying the extracted sugar by 0.9. d. Lignin and lignin-derived substances. This fraction is estimated by hydrolysis with strong sulphuric acid of the residue after the three fractions above have been removed. e. Nitrogenous materials or crude proteins. Table 12 gives representative examples of the chemical composition of a variety of peats (moss, grass, sedge and forest peat) from temperate and tropical countries. The figures are mainly for sub-surface layers which have not yet completely decomposed. The content of water-soluble compounds, mainly polysaccharides, mono-sugars, and some tannins, generally varies between five and ten percent depending on the stage of decomposition. These substances are the first to leach away on decomposition and highest contents are therefore found in the least decomposed materials. The figures in Table 12 reflect this but they also show that the original content of water soluble compounds probably depends on type of vegetation. The ether and alcohol extracts, determined separately by some workers, contain fatty acids, wax-like components, resins and nitrogenous fats, and some waxes, tannins, various pigments, alkaloids and soluble carbohydrates respectively. The amounts are strongly related to original vegetation. For example, Sphagnum peats may contain as much as 15 percent of soluble carbohydrates, reeds and sedge peats less than 5 percent (Lucas 1982). This fraction usually increases with increasing age of the peat. The cellulose and hemicellulose fraction decomposes easily and the content in the original vegetation is therefore usually greater than that in the derived peat. Again, the parent plant community influences the amounts, with woody peats commonly having a low content and papyrus having as much as 40 percent (Table 12). The general range is between 5 and 40 percent. The lignin and lignin-derived materials commonly constitute the largest portion of the peat because they increase in amount on decomposition as other materials are removed. Lignin is fairly resistant to microbial attack. The original vegetation also influences the content. Ranges from 20 to over 50 percent are possible. Tropical forest peats in particular appear to have considerable amounts of lignin and ligninderivates. Values of 75 percent for the Indonesian coastal lowland peats (Table 12) are not uncommon and similar values (56-73 percent) are found in Malaysia in comparable peats (Coulter 1957). The fact that tropical peats commonly have large contents of lignin and lignin-derived products is of some consequence for agriculture. Studies by Flaig (1968) on the effect of humic substances on plant metabolism indicate in particular that degradation products of lignin such as those with a phenolic character can cause interferences with essential processes and photosynthesis, even when present in very small amounts. Finally, the nitrogenous constituents which are small in comparison with the other fractions and mostly proteinaceous in nature. Total nitrogen may vary from 0.3-4.0 percent (on a dry weight basis). Because of its importance for agriculture nitrogen content is discussed in more detail elsewhere.

44

Table 12 CONTENTS OF PRINCIPAL ORGANIC COMPOUNDS OF TROPICAL AND TEMPERATE PEATS (% dry weight) (sources 1Lucas 1982; 2Ravikovitch 1948; 3Hardon and Polak 1941) The more or less traditional fractionation of organic compounds described above does not separate humic substances such as humic acids, fulvic acids and humins. Humic acid is separated by using 1 percent NaOH and subsequent acidification, the humic acids being the compounds insoluble in acid. The humins are not extracted by the NaOH solution but can be readily digested with cold 72 percent H 2 SO 4 . Such humic substances consist mainly of aromatic complexes and nitrogenous compounds chiefly composed of amino-acid residues. The possible origins of the aromatic complexes are lignin, tannins and polyphenols of the vegetable respiratory systems, whereas the amino-acid complexes seem to originate mainly from the cytoplasm of dead microorganisms (Kurbatov 1968). The contents of the above components are important for metabolic processes in plants. It is known, for example, that humic acid is an active auxin, promoting plant growth. Its effectiveness is however probably better shown in mineral soils with relatively little humic acid than in peats which are abundant in this substance. Elemental composition As shown in Table 13, from Lucas (1982), there is generally a wide variation in mineral composition between different peats, but the principal constituents other than carbon, hydrogen, nitrogen and oxygen are either silicon or calcium. The silicon usually comes from wind-blown minerals or washed-in sediments and is therefore small in amount. The calcium content can be large in eutrophic environments. Together with magnesium this element in its ionic form is strongly adsorbed onto the colloidal organic particles. Contents of iron, aluminium, sodium and sulphur reach high levels in some peats. This is usually caused by particular environmental conditions which operated during the paludification period. As a result of environmental changes the various layers of peat deposits often show differences in elemental composition. It is not clear whether tropical peats have elemental compositions essentially different from temperate peats. It is suggested, however, that since tropical soils commonly have larger sesquioxide contents than soils of temperate regions, that tropical peat-forming environments and the peats themselves might generally reflect such a difference by higher iron and aluminium contents.

45

Table 13 RANGE AND AVERAGE PERCENTAGE OF IMPORTANT ELEMENTS IN ORGANIC SOILS (source Lucas 1982) Percent range (oven dry)

Element

Eutrophic Peats lime rich

Al

Barium

Ba 0.0006 to 0.3

0.005

Boron

B

0.01

0.0001

Calcium

Ca 0.01 to 6.0

2.0

0.3

Carbon

C

12.0 to 60.0

48.0

52.0

Chlorine

Cl

0.001 to 5.0

0.10

0.01

Cobalt

Co 0.00 to 0.0003

0.0001

0.00003

Cu 0.0003 to 0.01

0.001

0.0005

H

5.0

5.2

Fe 0.02 to 3.0

0.5

0.1

Lead

Pb 0.00 to 0.04

0.005

0.001

Magnesium

Mg 0.01 to 1.5

0.3

0.06

Manganese

Mn 0.0001 to 0.08

0.02

0.003

Molybdenum

Mo 0.00001 to 0.005

0.001

0.0001

Nickel

Ni

0.0001 to 0.03

0.001

0.0005

Nitrogen

N

0.3 to 4.0

2.5

1.0

Oxygen

O

30.0 to 40.0

32.0

35.0

Phosphorus

P

0.01 to 0.5

0.07

0.04

Potassium

K

0.001 to 0.8

0.1

0.04

Silicon

Si

0.1 to 30.0

5.0

0.5

Sodium

Na 0.02 to 5.0

0.05

0.01

Sulphur

S

0.5

0.1

Copper

Hydrogen Iron

2

0.00001 to 0.1

2.0 to 6.0

0.004 to 4.0

0.5

Oligotrophic Peats lime poor

Aluminium

1

0.01 to 5.0

% Typical average

0.1

Zinc 3 Zn 0.001 to 0.4 0.05 0.005 1 Cupriferous bogs in Canada contained nearly 0.3% total Cu. 2 Samples with bog iron present could contain more than reported in this estimate. 3 6.7% of zinc has been reported present in the New York soils containing toxic amounts of zinc.

46

4.3.3 Acidity The pH of organic soils is related to the presence of organic compounds, the exchangeable hydrogen and aluminium, iron sulphide and other oxidizable sulphur compounds. In contrast with mineral soils, the presence of organic acids largely determines the acidity, and the presence of mobile or hydrolysable aluminium is less important. The range of acidity in organic materials is very wide. High-lime peats of eutrophic nature can have a pH of over 6, as, for example, in some peats in Florida (Lucas 1982) and low moor peats in the Netherlands. In conditions where there has been infiltration of brackish water the pH can be as high as 7.8 as in the Maldives where peat has developed in the inner part of atolls which had strongly saline initial conditions (Hammond 1971). On the other hand, peat can be very strongly acid where it contained pyritic materials which have been oxidized upon reclamation. The pH of such peats can reach values of less than 2. Tropical peats of ombrogenous and oligotrophic nature, which include most lowland tropical peats, are commonly acid or extremely acid with a pH range in water of 3 to 4.5. Variations within this range are caused either by admixtures of mineral soil which generally increase the pH, or by the specific location in the peatswamp. Surface layers of the dome-shaped peat deposits in the lowlands of Borneo have an average pH of 3.3 for the thickest peat whereas the shallow peat near the edge has an average pH of 4.3. This is consistent with findings elsewhere that in ombrogenous peats the environment becomes increasingly deficient in minerals so the youngest peats forming the uppermost layers, are poorest in cations causing extreme acidity. The pH of peat deposits can often give clues to mode of formation, type of peat and possible agricultural potential. It is an important parameter which can easily be determined. The natural pH should, however, be measured in the field because of the risk of oxidation in some peat soils of sulphur compounds which can drastically alter pH.

4.3.4 Exchange characteristics Cation exchange capacity (CEC) On decomposition organic matter produces a variety of organic compounds as discussed. These can exhibit exchange properties which play an important role in the agricultural management of soils, and in particular in manipulating the chemical fertility. The exchange capacity of both mineral and organic soil materials depends on the number of negatively charged exchange sites. These adsorp cations Ca, Mg, K and Na which replace the hydrogen ions at the sites. It should perhaps be remarked here that in organic materials there is another type of cation adsorption by so-called organo-metallic compounds which are responsible for the fixation of copper and zinc. In general, however, the ion adsorption and exchange is associated with the hydrophilic colloids of the peat, namely the humic acids and hemicelluloses (Volarovich and Churaev 1968). The main one is the carboxyl radical. Apparently the sites located inside loose particles of hydrophilic colloids take part in the ion exchange as well as sites on the main surfaces. This not only explains the high exchange capacity usually found in peats but also the length of time (one to two hours) it takes to reach equilibrium. There are various methods to determine the CEC of soils and since there is no international agreement it is difficult to compare results. In addition the CEC of peat is highly pH-dependent. This is because the hydrogen ion remains tightly associated or fixed with the functional group in acid materials and does not exhibit exchange properties. A third problem is that CEC is greatly influenced by drying, reductions ranging from 20-70 percent have been reported.

47

The acidity of the exchange medium appears crucial. Studies by Helling, Chesters and Coey quoted by Lucas (1982) show 73 me/100 g at pH 3.5, 127 me/100 g at pH 5.0, 131 me/100 g at pH 6.0, 163 me/100 g at pH 7.0 and 215 me/100 g at pH 8.0. The cation used in the exchange medium is also of importance. Exchange efficiencies are reported to be Na
1 1

Saw-grass

1

Location

CEC in mlgr.

Finland

140

Finland

70

Finland

100

Florida, USA

208

Forest (woody)

2

Malaysia

106

Forest (woody)

3

Indonesia

125

Forest (woody)

4

Ivory Coast

23.0 (other method)

Although the CEC values for organic materials appear to be large in comparison with those of common mineral soils this must be considered in the light of the low bulk density of the peaty materials. For proper comparison, values must be reduced by a factor related to the difference in bulk densities. Lucas (1982) illustrated the agricultural importance of expressing CEC on a volume basis rather than on a weight basis as follows (Table 15):

48

Table 15 COMPARISON OF CEC VALUES ON A WEIGHT AND PER VOLUME BASIS (source Lucas 1982) Soil type

CEC by weight me/100g

CEC by volume me/100 cc

Loam soil

12

14

Sphagnum peat

100

8

Woody peat

90

14

Muck

200

60

On a volume basis, the same amount of lime would be required for the loam soil as the woody peat to make the same change in the percentage calcium saturation. On a weight basis the woody peat appears to require 7.5 times more than the loam soil. Exchangeable cations and base saturation The exchangeable cation status of organic materials is difficult to indicate since different cations are complexed to differing degrees by the organic compounds. Trivalent cations are more strongly adsorbed than monovalent or divalent ones, but their selectivity of peat for hydrogen ions is much greater than for the metal ions. It is generally agreed that the two cations, H and Ca, usually occupy most of the exchange sites (Lucas 1982), but this is not always so. Peat in Sarawak of an oligotrophic and ombrogenous nature, investigated by Tie and Lim (1976), appears to have much larger values for exchangeable Mg than for calcium. It seems therefore that local conditions can change the general dominance of calcium. The proportion of the total CEC taken up by Ca, Mg, K and Na is commonly known as the base saturation value, the remainder of the CEC being the acid part (H and Al). It has already been remarked that pH and calcium saturation are strongly related. This can be said also for the base saturation in general. Differences are caused by several factors, namely the form and the amount of pH dependent organic compounds, the difference in the dissociation constants of the humates and the amount of other cations. Of the latter the amount of exchangeable aluminium is of particular importance. This is discussed in more detail in relation to lime requirements in Chapter 8. Base saturation values vary not only as a result of pH differences but also according to the kind of peat. Low moor eutrophic peats which are saturated with water of a high mineral content, often show values greater than 100 percent with calcium dominant. Oligotrophic high moor peat, of low pH, appears to be saturated with hydrogen and base saturation values of less than 10 percent are common (Tie and Lim 1976).

4.3.5 Organic carbon The percentage of organic carbon in peat is probably of most value to those interested in it as a source of fuel. Its assessment is needed also for agricultural purposes, particularly for calculating the C/N ratio of the material. The C/N ratio indicates the degree of humification of the peat and the likelihood of nitrogen consumption by micro-organisms when the peats are fertilized on reclamation. 49

Table 13 indicates that the organic carbon content of peat can vary from 12-60 percent. This large range reflects the kind of organic materials, the stage of decomposition and probably also the analytical method used. Most information from agricultural scientists is based on the Walkley Black wet oxidation method, which is not a true measure of total organic carbon. Because of inconsistencies in analytical procedures it is only possible to make some general observations on reported carbon contents. Ekono (1981) in their review of peat as a source of energy indicate organic carbon values of 48-50 percent in slightly decomposed (fibric) peat, 53-54 percent in moderately decomposed (mesic) peat, and 58-60 percent in highly decomposed (sapric) peat. They conclude that although highly decomposed peats have higher organic carbon values than less decomposed ones, the difference on decomposition is never more than 10 percent. Kanapathy (1976) in his research on peat soils in Malaysia found values ranging from 58 percent in the surface soils to 25 percent in subsoils. Perhaps there is some admixture of mineral soil in the lower layers but higher carbon content in the surface samples also reflects decomposition. Studies by Tie and Lim (1976) in Sarawak show a range of 20-38 percent whereas values of around 50 percent are given for Indonesia. Both studies, however, indicate a higher content of organic carbon in the surface horizons of deep peat soils than in shallow ones. This may be consistent with the fact that the uppermost layers of deep peat are usually ombrogenous and oligotrophic in nature with a large component of ligneous woody materials whereas the shallow peats are more mesotrophic in nature containing fewer such materials. It is interesting to study the relation between loss on ignition and percentage of organic carbon. Shallow peats always have a higher ratio of loss on ignition to percentage carbon content than deep peats. In Sarawak (Tie and Lim 1976) the ratio is 4 for the shallow peat, to 2.5 in the deep peat; values of around 2 appear to be most common. In this connection it is interesting to note that Soil Taxonomy (Chapter 5) uses organic carbon content to distinguish organic soils from mineral soils. In Soil Taxonomy 12 percent organic carbon is taken to be equivalent to 20 percent organic matter. Thus a ratio of approximately 1.65 is used. Evidence from oligotrophic tropical peats indicates that the use of a ratio of 2 or more probably reflects the actual situation better.

4.3.6 Nitrogen The nitrogen content of peat soils is of considerable importance to agriculture. Most of the nitrogen is in the organic form but small quantities of nitrate are usually present in better drained soils in which organic materials oxidize rapidly. The micro-Kjeldahl method is most commonly used to determine nitrogen. As is the case with organic carbon the nitrogen content can also vary widely showing a range of 0.3-4.0 percent (Table 13). According to Lucas (1982) peats developed from reeds, sedges and trees are generally two to four times higher in nitrogen than those formed of Sphagnum mosses and Eriophorum sedges which contain less than 1 percent even though the original plant materials contain 1-5 percent. In the Everglades there is an opposite effect. Here, saw-grass contains 1 percent nitrogen and its peat residues 3 percent. No doubt, the degree of humification and relative accumulation of nitrogenous compounds, such as proteins, are important factors in creating such differences. Ravikovitch (1948), in his study on the Huleh valley peats in Israel, indicates that the nitrogen percentages of the peats are high, ranging from 1.53-2.87 percent, whereas the nitrogen content of the papyrus (the original vegetation) was only 0.56 percent. He did not find any nitrates or nitrites and attributes the absence of the former to the anaerobic conditions. 50

Hammond (1971), in his study of the Maldive peats, found values of 2.3 percent in the surface. These he considered moderate levels. Values decreased with depth to 1.5 percent in the lowest layer. This gradual decrease in nitrogen content, with depth, appears to be a general characteristic of all peats as this was also found to be the case in South East Asia. Kanapathy (1976) found values of 1.88 in the surface to less than 1.50 below 60 cm depth. It should be noted, however, that these figures are expressed on a dry weight basis. Considering that the bulk densities of surface layers are commonly greater than those of sub-surface layers because of the effect of decomposition, it is reasonable to assume that when the nitrogen contents are expressed on a volume basis the conclusion may have to be reversed. In this connection Driessen (1977) is worth quoting: “A normal peat soil with bulk density of 0.1 g/cm3 and a nitrogen content of 2 percent contains only 2 000 kg N/ha in its upper 10 cm (assumed wood-free), whereas a mineral surface horizon with only 0.5 percent N but a bulk density of 1 g/cm3 contains 5 000 kg/ha. In this light, values for nitrogen content of over 2 percent which are generally considered to be high should be considered as low”. Similar misinterpretations of analytical results are repeatedly made in the literature. The problem of assessing the required nitrogen levels in peat soils for crop production and the changes in nitrogen contents following reclamation is dealt with in detail in Chapter 8.

Nitrogen levels in surface layers of deep peats are generally higher than those in shallow soils. Tie and Lim (1976) found values of between 0.50 percent and 2.05 percent in the topsoils of shallow peat but values of 1.10-1.67 percent in those of deep ones. These findings are supported by work carried out by Suhardjo and Widjaja-Adhi (1977) on similar peats in Indonesia, in which the surface layers (30 cm thick) of deep peats appeared to have higher levels of nitrogen than those of shallow peat (1.98 percent as opposed to 1.13 percent). Thus with increasing age, or development, the nitrogen content of the peat seems to increase independently of the degree of decomposition. This seems illogical as it is generally assumed that the most recent peat layers are poorest in nutrients (oligotrophic surface layers as opposed to eutrophic sublayers). The differences cannot be explained by attributing them to differences in bulk density. It is also inconsistent with the observation that surface layers commonly have a higher proportion of ligneous materials characterized by high C/N ratios and responsible for the higher levels of organic carbon noted above (Section 4.3.5). Comments made by Hardon and Polak (1941) might offer some explanation. They argue that the tropical ombrogenous oligotrophic peat already contains an initial high content of lignin, but a low content of cellulose. Micro-biological activity characterized by nitrification and cellulose destruction removes much of the original nitrogen, the remaining nitrogen being largely present in the lignin, the proportion of which increases as the peat decomposes.

4.3.7 Phosphorus Organic soils in virgin conditions usually have very low phosphorus contents. Table 13 indicates a range of 0.0-0.5 percent on a dry weight basis but the average for oligotrophic peats, common in the tropics, is less than 0.04 percent. Most phosphorus is present in the organic form and must be mineralized first before it is available to the plant. A problem in comparative studies is that organic phosphorus is not included in standard analyses. Available phosphorus values depend very much on the extraction method used. The general problem of expressing analytical values on dry weight instead of as volumes also once again makes it difficult to make valid general observations. Total phosphorus levels in oligotrophic peats from Sarawak range from 400-1 000 ppm (0.004-0.01 percent). Similar peats in peninsular Malaysia reported by Kanapathy (1976) have values of 0.0020.006 percent whereas those in Indonesia are around 0.006 percent. Tie and Keuh (1979) quoting work by Wall found clear indications that in coastal swamps phosphorus levels decrease both with depth and with the thickness of the peat deposits. This may be related to the causes of similar trends in nitrogen content.

51

4.3.8 Free lime (CaCO 3 ) The amount of free lime in peat soils is commonly negligible. Some eutrophic peats have free calcium carbonate mainly derived from shells. In other peats small amounts of calcium carbonate originating from marl or limestone, or from bicarbonate-saturated solutions are found. Lime-rich peat soils are extremely rare in tropical countries, and they are only developed under exceptional conditions. One such case is in the Maldives where peats have developed in the inner basins of coral reefs. The lime content of such peats can be over 1 percent, which is less than the average level of 2.0 percent found in eutrophic peats. The average level of calcium in oligotrophic peats and thus of most tropical peats is less than 0.3 percent. The problems caused by excessive lime rarely arises in tropical peats.

4.3.9 Sulphur Some peat soils are well known for their high sulphur contents. Peats in tropical coastal lowlands, for example those of the Orinoco delta of Venezuela, often contain considerable amounts of sulphur often in the form of pyrite (FeS 2 ). This mineral forms under anaerobic conditions during the initial stage of peatswamp development in the presence of brackish or sea-water and becomes lodged in the root channels of existing vegetation. Pyrite formation is also very common in papyrus swamps in East Africa. High sulphur contents in peats are commonly associated with mineral soils, the so-called potential acid sulphate soils, either underlying the peat or formed in mineral layers within the peat. As well as the areas mentioned above, all coastal regions in the tropics with peat soils are suspect. In the special case of the peat in the Huleh Valley, Israel (Ravikovitch 1948), gypsum accumulated during the process of paludification. This has caused SO 3 levels of as much as 7 percent in the organic materials. The presence of sulphur compounds in the organic materials can lead to strong acidification of the peat after drainage and reclamation. This acidification is caused by the oxidation of the materials upon exposure to air. If sufficient free calcium is present, calcium sulphate (gypsum) forms and this neutralizes the acids. In most situations, however, calcium is not present and the pH of the soil falls, in some circumstances to 2.0 or less inhibiting the growth of most vegetation. The presence or absence of sulphuric materials in organic soils is used to classify peats according to the Soil Taxonomy (Chapter 5). This is useful in practice because high sulphur levels (generally above 1 percent) indicate potential difficulties when the peats are reclaimed. This is discussed in more detail in Chapter 7.

4.3.10 Trace elements Organic materials are commonly deficient in micronutrients frequently causing crop failures after reclamation. This is caused by the formation of organo-metallic compounds. The carboxyl and phenolic groups found in decomposing peat are important functional groups for bonding metals. The attraction order has been found to be Cu>Pb>Zn>Ni>Co>Mn>Ca>Ba. This is why copper is deficient in most crops in newly reclaimed peat. The copper content in virgin organic soils ranges from 2 to 20 ppm, values too low for satisfactory growth of most crops (Lucas 1982). There are few analyses available for copper or trace elements in tropical peats. Tie and Lim (1976) report that Sarawak peats contain only 1 ppm Cu and that Morgan-extractable copper is almost absent. Zinc, iron and manganese were 14, 49 and 43 ppm respectively (0.1 N extractable), but 5, 35 and 50 ppm respectively in Morgan’s extract. The lack of standard analytical methods makes it difficult to compare reported levels. The Peat Research Institute of Finland advocates the use of Morgan’s extract, but Sarawak peats gave the best recovery of added copper with EDTA (1 percent) followed by 0.1 N HCl. 52

Analysis for copper in virgin lowland peat from Indonesia by a neutron activation technique gave values of 20, 11, 8 and 3.3 ppm respectively in layers at depths of 5-10, 10-20, 80-90 and 120-140 cm. Drained and cropped forest peat had much lower values of 2.5,1.3, 2.3 and 1.2 ppm respectively for layers of comparable depth. It is significant that copper is highest in the upper layers. This may be because copper is constantly recycled by successive generations of vegetation and saved from leaching (Driessen and Sudewo 1977). The role of trace elements and in particular that of copper in agricultural management is discussed in more detail in Chapter 8.

4.4 Biological Activity The biological activity of organic materials is related to the kinds and amounts of micro-organisms present. Micro-organisms play a dominant role in the decomposition and mineralization of organic matter and since these processes appear to contribute most to peat wastage following reclamation and drainage, it is appropriate to pay some attention to them. The broader aspects of the process of peat wastage and subsidence is described and discussed in detail in Chapter 7. Waksman (1942) conveniently subdivides micro-organisms in peat soils info three groups: i. Organisms present during the initial stage of decomposition of fresh organic deposits. Most of these belong to the actinomycetes, fungi and bacteria largely responsible for rapid decomposition of freshly accumulated materials at the surface. In particular they play a role in the degradation of cellulose, hemicellulose and some of the proteins. As indicted in Chapter 3 the initial aerobic stage in peat development is followed by an anaerobic stage characterized by the presence of different micro-organisms. ii. Organisms which develop and remain present in deeper peat for most of the time that the peat is below the groundwater-table. These organisms like anaerobic conditions and obtain the oxygen they require from the organic materials which they oxidize and decompose. They produce gasses rich in hydrogen (such as methane) and sulphides. Most of the waste products are derived from the decomposition of cellulose, proteins and other complex organic compounds. iii. Organisms which become active when the peat is drained and so aerated. They are dominantly fungi, aerobic bacteria and actinomycetes similar to those present in the initial stage which decompose the remaining organic materials, the lignins, most resistent to degradation. According to Volk (1973) 58-73 percent of the reported subsidence in the Everglades peats is the result of microbial activity, and there is no reason to assume that this would be different in tropical peats. In fact most workers agree that because of the higher temperatures in the tropics microbial activity increases substantially. It is possible to assess quantitatively the number of bacteria present in peat soils. Waksman and Stevens (1929) record counts in New Jersey for high lime peats, sampled at depths of 30 and 120 cm, with 350 000 and 100 000 organisms per gram respectively and 32 million to 1.6 million respectively at corresponding depths in peat in Florida. Both these sets of figures show a decrease with depth. This is not always so as is indicated by counts in low lime peats containing mostly acid resistant anaerobic bacteria. Such soils had 100 000 organisms per gram near the surface compared to 2 million at a depth of 240 cm. The quantity of organisms, however, tends to decrease with increasing pH. Azotobacter (nitrogen fixing bacteria) and nitrifying and cellulose decomposing bacteria were absent in these lime-poor oligotrophic peats. However, azotobacter may be present at the higher pH values usually found in eutrophic peats.

53

Tate (1980) shows that depth has a considerable effect on microbial activity. He studied carbon metabolism on various compounds at depths of 0-10 and 60-70 cm. There were in general considerable changes with oxidation of the substrates, but the changes in the contribution of each substrate to total aerobic respiration were more moderate. It is interesting that, although a measurable decline in aerobic oxidation was observed at the depths studied, considerable aerobic respiration was still occurring between 60 and 70 cm depths. This supports the hypothesis that aerobic microbial activity occurs to much greater depths in organic soils than in mineral soils, probably as a result of greater diffusion of oxygen in the former. Interesting extrapolations can be made from this data by comparing microbial activity at various soil depths and the effect of watertable depth on subsidence rate. Subsidence rates appear to vary linearly with depth of the watertable, but microbial activity declines between the soil surface and 60-70 cm depth. The subsidence rates are almost the same however at each soil depth, although the microbial activity at 60-70 cm is only 40 percent of that at the surface. Comparison of changes in bulk density with variation in microbial activity resolves this discrepancy. Tate (1980) also shows that cropping of organic soils influences the overall carbon oxidation rates. This is particularly so under grassland which contributes fresh organic materials to the soils. Crops which are removed such as sugar cane did not show such effects. In general, water-table control appears to be the optimum method to control decomposition, and subsidence of organic soils.

4.5 Characteristics of the Peatswamps 4.5.1 Geomorphology 4.5.2 Hydrology

The hydrological and topographical characteristics of peatswamps are of particular importance to those interested in water management aspects. The hydro-topography must be adequately known before any attempted reclamation. This is necessary whatever the purpose of reclamation. The properties discussed below are subdivided into two groups dealing with the geomorphological and hydrological aspects respectively (Table 6).

4.5.1 Geomorphology Topographic situation The topographic situation characterizes the position of the peatswamp in relation to surrounding landscape units. The following situations are found in the tropics. a. Deltaic peatswamps b. Coastal basin peatswamps. c. Lagoonal peatswamps. d. Small inland valley peatswamps. e. Major valley peatswamps. f. Meander bend peatswamps. g. Isolated small bottomland peatswamps. h. Atoll peatswamps. This list does not cover every possible situation and the units can be subdivided or others added if the need arises. In Chapter 5 examples of such geomorphological units with their horizontal and vertical dimensions are given in Figures 12 to 17. 54

Description and definition of the geomorphological setting provides a useful background and gives some indication of the properties of the organic materials likely to be found. Chapter 3 describes the close relationships between the mode of formation and the characteristics of the organic deposits. If in the preliminary stages of peatswamp investigations the type of swamp is established, it is then easy to list the likely characteristics of that particular type of peatswamp that need detailed investigation in subsequent stages. Surface configuration The size and form of the swamp, its areal extent and limits should be surveyed so the possibilities and scale of reclamation can be considered in context. For many reasons it is not advisable to reclaim and develop peatswamps piecemeal. Piecemeal reclamation invariably results in difficulties with water management. A scheme can only be evaluated properly when the peatswamp is seen as a whole. It is then possible to commence reclamations in the right order and in the right places. The surface configuration needs to be known well and this requires mapping of the entire swamp at an adequate scale. A scale of 1:50 000 is usually satisfactory for reconnaissance purposes, but scales of 10 000 or larger are needed to plan properly. Elevation of surface Surface elevation in relation to established benchmarks gives important clues to drainage possibilities. Many peatswamps in the tropics have a dome-shaped surface. The central parts of many tropical swamps, for example the large mature coastal swamps of South East Asia, rise many metres above the normal flood level of the nearby rivers. The highest part of the dome is in some cases eccentric and close to the river. Detailed level surveys are thus essential for the design of effective arterial drainage. Figure 6 gives cross-sections of Sarawak coastal peatswamps. They show the domed and ombrogenous nature of the swamps. The Sungei Assan section shows that small hillocks have been completely blanketed by peat. Little information is available on the nature of valley peats. The oligotrophic and ombrogenous nature of most valley peats in South East Asia can usually be easily assessed, but, where surrounded by hills it is not always possible to appreciate their raised dome-shaped nature at first sight. Figure 7 illustrates valley peat in Rwanda. Here the peat is partly covered by mineral, possibly colluvial, material and has raised surfaces at its margins bordering the hills. There is no evidence of doming. Such situations are also quite common in inland valley peats in Indonesia and Malaysia (Andriesse 1974). Figure 6. Peat profiles in the Rajang delta and Baram river (source Anderson 1964) Figure 7. Pedo-topographical cross-section of valley peat in Rwanda (source Grontmij 1978) The microtopography of peat surfaces is often irregular and hummocky. In areas with grassy vegetation, a type of gilgai topography as a result of tussock development is common. Run-off after flooding often induces small-scale gullying in the soft organic materials. This effect can be accentuated by reclamation efforts. In forest peat areas the aerial roots of many swamp trees form stools which can be more than 50 cm higher than surrounding land surface which is frequently flooded. Microtopography, whatever its origin, makes it difficult to level the land surface accurately during the initial survey because constant adjustments are needed.

55

Elevation of the underlying mineral soil The underlying mineral materials can also have a very undulating surface (Figs. 6 and 7). In reclamation this can interfere with artificial drainage. On drying out the peat surface subsides irregularly because of the differences in the thickness of the deposits and the degree of decomposition. This gives a changing surface configuration different to the original. Knowledge of the elevation of underlying mineral materials is valuable when assessing the maximum drainage depth. Because drained peat deposits will eventually disappear, the drainage lay-out and depth has to be adjusted from time to time. It is essential to know at what stage gravity drainage will fail and pumping will be required to keep groundwater at a satisfactory level. Figure 8 illustrates such a situation. In coastal areas the elevation of the peat surface and that of the mineral subsoil and their relationship to the mean sea level are of particular interest. The risks of salt- or brackish water incursion as a result of subsidence must be assessed. Where the surface of the mineral subsoil is below the mean sea level, a situation which is quite common in some areas because of the strong link between sea level changes and peat development (Chapter 3), the risk of salt incursion are very great. In the initial surveys of the peatswamps, levelling of the surface should therefore be backed up by a survey of the peat depth so that two types of contour maps can be drawn, one showing the surface of the peat before drainage and one predicting the situation when the peat has disappeared. Figure 8. Possible stages in peat subsidence after drainage (source Andriesse 1972) Fig. 9. Extent of surface peat deposits greater than 3 m thick at Negril in Jamaica (source Robinson 1980)

56

57

Figure 9 shows a lagoon in Jamaica where peat has developed behind coastal coral-sand bars cutting-off drainage to the sea. The irregular depth of the peat, which possibly reflects the surface of an underlying limestone with karst features, is shown by the peat depth contours. From this sketch map it is possible to visualize the irregular landscape surface with many local hollows which would arise after the peat had disappeared.

4.5.2 Hydrology Water sources and quality The nature and quality of the water in peatswamps is relevant to its potential use in agriculture and in other ways, for example, its quality as drinking water. The sources of the water should be carefully investigated and its quality should be analysed by traditional methods. Water from swamps containing large amounts of organic deposits are usually brown to black stained and very clear. The typical coffee coloured characteristic of water from peatswamps has given rise to many river names, for example, Rio Negro in Brazil, and the many rivers in Malaysia and Indonesia with the name Sungei Merah (brown river) or Ayer Hitam (black water). Investigations in Brazil show that such water contains organic substances which are alleged to have an antibiotic action making the water sterile. Some rivers show few signs of micro-biological activity and have no algae or fish. Drainage water from oligotrophic peats is very low in nutrients and this by itself may be sufficient reason for the low biological activity. Drainage water from eutrophic peats may have 50 ppm or more of basic cations (Ca, Mg, K and Na), but water from oligotrophic peats generally contains less than 5 ppm. Waters with high conductivity readings (<1 000 mmhos/cm or 640 ppm of salt) are most likely contaminated from brackish sources. It is best not to use them for irrigation. Sprinkler irrigation is common practice on drought-prone peat soils in climates with prolonged dry periods. Some acid waters from peatlands carry excessive amounts of iron compounds which precipitate as sludge when water of higher pH is met. The author has noted marked accumulations of such materials in drains on the fringes of fresh water coastal swamps where they pass into brackishwater Mangrove/Nipah swamps. These iron precipitates sometimes clog drainpipes completely. Water from peatswamps can also introduce plant diseases and nematode infections if it comes from stagnant streams or ponds. Water stagnation causes the accumulation of decomposition products of the peat which when sufficiently concentrated is noxious to plants. Some peat water may contain sulphates toxic to many plants because of the oxidation of pyrite in drained peats. Peat water, particularly water from oligotrophic tropical peats is usually of low quality as drinking water. It is deficient in most trace-elements particularly iodine. Position of natural drainage channels In many peatswamps it is difficult to trace the original drainage lines. In the rainy season, when most of the peatswamps are partly inundated, it is often difficult to locate drainage channels. The so-called floating peats are particularly difficult in this respect. There is a good example of these in the Yala swamps bordering Lake Victoria, Kenya. Here, a layer of partly decomposed peat 10 to 20 cm thick and an underlying dense rootmat, float on the subsurface water in the wet season (ILACO 1975). In such circumstances the peat surface collapses when deep drainage is attempted.

58

Topographical surveys should therefore try to locate the main drainage lines, because they can be used as outlets in drainage scheme design. Existing natural drainage lines usually indicate the local presence of shallow peat because the better drainage has resulted in a higher decomposition rate of the peat. In some instances it is possible to locate such drainage lines on air photographs if they are sufficiently large scale, by using differences in vegetation as indicators. This method has been used successfully in Sarawak.

59

5. CLASSIFICATION 5.1 Introduction 5.2 Historical 5.3 Classification Systems 5.4 Conclusions 5.5 Recommended Approach 5.6 Classification of Organic Soils According to Soil Taxonomy 5.7 The Classification of the Physical Environment

5.1 Introduction The classification of peats and organic soils poses many problems. As indicated in Chapter 1, this Bulletin is primarily directed at management aspects of organic soils related to agricultural use and productivity. The management of peats, however, not only depends on the character of the peat soil as a growing medium for plants, but also on the environment, particularly the topographical situation and climate. Characterization and classification of organic soils without regard to the physical environment in which they are found tends to over emphasize the agronomic aspects rather than the required overall management. Hydrological aspects of management should receive proper attention, so the classification of organic soils should cover both pedological and topographic or geomorphological aspects.

5.2 Historical The study of peatlands as a special form of wetlands has always been very much the domain of naturalists, more specifically botanists and biologists. Peat science is an established flourishing sector of the biological sciences, as is shown by the activities of the International Peat Society with its many national branches. The proceedings of the four-yearly International Peat Congresses record a wealth of information on the activities of national peat research institutes, other organizations and individual research workers throughout the world. It is perhaps unfortunate, however, that most of the papers do not deal with agronomic aspects and few deal with tropical countries. Peat science is best developed in the USSR, Finland, Ireland, the two Germanys, Canada and the USA. It is often, however, of a fundamental nature or oriented towards the use of peat for fuel or other industrial purposes. The USA is probably an exception to this. Most papers on the agricultural use of peat are found in soil science and agronomy journals. Most of our knowledge of peat and peatlands comes from northern Europe and North America where large peat bogs have been reclaimed for centuries. Since inputs from several disciplines are required for management purposes, this Bulletin discusses classification problems at some length. The main aspects of the various classification systems are dealt with below. An excellent review of peat classifications by Farnham (1968) was further expanded by Farnham and Finney (1965). These papers with their recommendations for improvement have strongly influenced the subsequent classification of Histosols in Soil Taxonomy (Soil Survey Staff 1975) which is being further developed and expanded to serve as an international system.

60

5.3 Classification Systems 5.3.1 Introduction 5.3.2 Topographical classification 5.3.3 Classifications based on surface vegetation 5.3.4 Classifications based on chemical properties 5.3.5 Classifications based on botanical origin 5.3.6 Classifications based on physical characteristics 5.3.7 Classifications based on genetic processes

5.3.1 Introduction Existing classification systems are based on: i. Topography and geomorphology. ii. Surface vegetation. iii. Chemical properties of the peat. iv. Botanical origin of the peat. v. Physical characteristics of the peat. vi. Genetic processes within the peatswamp. The following discussion is cross-referenced to Chapters 3 and 4.

5.3.2 Topographical classification Topographical classification systems deal primarily with aspects of landscape. The hydrological conditions, the origin of the peatswamp, the nature of the accumulated material are all related to topography, so topographical classifications are useful for indicating possible limitation on reclamation and necessary management procedures. A typical example of a topographical classification is that used in Ireland in which the distinction is made between Blanket Bogs and Raised Bogs. Blanket Bogs are moderately deep accumulations (average 2.6 m thick) on gentle to strong slopes. Raised Bogs are deep peats (average 9 m thick) developed on flat central plains (Hammond 1981). Weber (quoted by Farnham and Finney 1965) divided German bogs into three types based on surface configuration, namely low moor, transitional moor and high moor. In this scheme low moor occupies the low ground (bottom lands), whereas high moor is found at higher elevations, in very similar fashion to the raised bogs of the Irish classification. High moor rises above the original groundwater level, the present groundwater level being maintained by the peat itself. Low moor starts to develop in the presence of groundwater and alluvial sediments rich in nutrients (Fig. 2) forming primary peat. In the high moor stage the only source of nutrients is precipitation, the surface being beyond the influence of flooding and secondary and tertiary peats are formed. There is thus a strong link with the genetic origin of peatswamps and topography. Classifications based on mode of occurrence use terms such as Marine and Freshwater Swamps, Valley Peats and Upland Swamps. Anderson (1964) and Andriesse (1974) attempted to classify tropical peats in Malaysia using topography. Anderson’s scheme takes into account the nature of vegetation as the term Mixed Freshwater Swamp Forest indicates. Andriesse, however, advocates a classification of peatswamps purely on their geomorphological setting (the physical environment). 61

5.3.3 Classifications based on surface vegetation Peatlands or swamps can be classified according to the present vegetation cover, as is done in Canada and northern Europe. For our purpose, such systems are of interest only if there is a relation with management requirements and, particularly, reclamation problems. The costs of clearing and accessibility of the land are affected by the vegetation. The vegetation cover is often a key indicator of other, not immediately obvious, inherent characteristics of significance when assessing potential agricultural use. In this way vegetation could serve a useful purpose as a parameter in classification.

5.3.4 Classifications based on chemical properties Several classification systems are based on chemical properties, not so much on the properties of the peat material itself as on properties of the environment. The distinction into eutrophic (nutrient rich), mesotrophic (moderately rich) and oligotrophic (nutrient poor) organic soils applies to both the peat material and to the hydrological conditions. There is a strong link between chemical classification systems and mode of origin and topographic situation. Eutrophic peat environments are characterized by flooding with nutrient rich water, whereas oligotrophic peats are fed by nutrient-poor water, mainly precipitation, so such peats must already have grown above the flood level of nearby rivers. Peats can be classified on their inherent chemical properties as well as their general chemical environment. Such classifications are mainly based on the fractionation of organic chemical compounds. Peats are classified in this way using the amounts of water-soluble substances; the ether and alcohol soluble substances; the cellulose and hemicellulose content; the lignin and lignin-derivatives and the nitrogenous constituents. Though these properties are used mainly to assess the potential of the peat material for industrial use they can also be used to predict decomposition rate which in turn often reflects fertility for agricultural purposes. They influence exchange characteristics, leaching and fixation of fertilizers and in particular the availability of trace elements.

5.3.5 Classifications based on botanical origin The botanical origins of peat features highly in several classification systems. Frequent reference is made in the literature to Sphagnum peat which is extensive in temperate and tundra regions. It occurs also in the tropics at high altitudes, for example, in Rwanda/Burundi. Peats can be divided into major vegetation types such as moss peat, sedge peat, heath, saw-grass peat, Cyperacea peat and forest or woody peats. One of the problems of this type of classification is that peat deposits are often characterized by vertical sequences or layers of peat of different vegetative origin, each layer indicating a specific stage in the development of the deposit. In Sarawak, for example, it is common to find remnants of original mangrove vegetation at the deepest level, overlain by transitional brackish-water forest species, passing upwards into a freshwater swamp vegetation near the surface (Anderson 1964). An understanding of the botanical composition of peat is valuable because many of the other characteristics of peat are related to it. For example, peats developed from reeds, sedges and various trees are generally two to four times richer in nitrogen than those from Sphagnum mosses and Eriophorum sedges (Lucas 1982). Lignin content is likewise often related to botanical origin. Woody peats generally contain low contents of cellulose and hemicellulose and large amounts of lignin. Since cellulose and hemicellulose decompose easily and lignin is the resistant fraction, the proportion of the latter increases as the peat decomposes, particularly in woody peats. Reed and sedge peats do not decompose readily. It is therefore essential to know the vegetative origin of the peat for management purposes. Its origin has a bearing on decomposition rate, and thus on reclamation procedures. The wood content is also significant when considering the economic feasibility of reclamation and potential use. 62

5.3.6 Classifications based on physical characteristics Probably the first worker to classify peat on physical properties was Von Post who developed a field method to indicate stages of decomposition. The Von Post scale (Table 16) recognizes 10 steps; little decomposed fibrous, light-coloured peat being defined as H1, whereas the well decomposed, colloidal, dark-coloured material at the other end of the scale is indicated as H10. Root fibres, wood residues and degree of moisture are also indicated. This scheme, although it is still widely used, particularly in northern Europe, suffers from two shortcomings. First, it is subjective in application, and second there are too many categories. However, modern classification systems including Soil Taxonomy have adopted the principle of using decomposition stages to characterize peat materials. In Soil Taxonomy the Von Post scale has been narrowed down to three stages, namely the fibric, mesic and sapric types which are quantitatively defined by analysis of fibre content and size to remove the subjective bias. Other morphological criteria, including colour, amount of mineral matter, structure and thickness of the deposits are used in modern systems to characterize peat soils. Schemes based on these criteria are particularly valuable in the assessment of the agricultural value of peat.

5.3.7 Classifications based on genetic processes Classifications using assumed genetic processes are based mainly on the climate under which peat was formed and changes in the peat, including those as a result of a soil forming process, after reclamation. In the Russian system genetic origin is used at a high categorical level. Terms like Temperate Peats or Tropical Peats, however, are not very helpful in management practice, nor do they indicate possible agricultural use. Changes caused by reclamation and soil forming processes can be very rapid and short-lived, particularly in the tropics, so they are not useful as classifying parameters.

5.4 Conclusions The overview of classification systems in the sections above leads to some conclusions. There are many classification systems, each geared to the objectives of the disciplines responsible for their development. Many of these systems were set up in isolation, often nationally. This gives them a local bias and an emphasis on known conditions. Some confusion is caused because a common terminology is used by these classifications but with different connotations.

63

Table 16 THE VON POST SCALE OF HUMIFICATION (source Ekono 1981) Symbol

Description

H1

Completely undecomposed peat which, when squeezed, releases almost clear water. Plant remains easily identifiable. No amorphous material present.

H2

Almost entirely undecomposed peat which, when squeezed, releases clear or yellowish water. Plant remains still easily identifiable. No amorphous material present.

H3

Very slightly decomposed peat which, when squeezed, releases muddy brown water, but from which no peat passes between the fingers. Plant remains still identifiable, and no amorphous material present.

H4

Slightly decomposed peat which, when squeezed, releases very muddy dark water. No peat is passed between the fingers but the plant remains are slightly pasty and have lost some of their identifiable features.

H5

Moderately decomposed peat which, when squeezed, releases very “muddy” water with a very small amount of amorphous granular peat escaping between the fingers. The structure of the plant remains is quite indistinct although it is still possible to recognize certain features. The residue is very pasty.

H6

Moderately highly decomposed peat with a very indistict plant structure. When squeezed, about one-third of the peat escapes between the fingers. The residue is very pasty but shows the plant structure more distinctly than before squeezing.

H7

Highly decomposed peat. Contains a lot of amorphous material with very faintly recognizable plant structure. When squeezed, about one-half of the peat escapes between the fingers. The water, if any is released, is very dark and almost pasty.

H8

Very highly decomposed peat with a large quantity of amorphous material and very indistinct plant structure. When squeezed, about two-thirds of the peat escapes between the fingers. A small quantity of pasty water may be released. The plant material remaining in the hand consists of residues such as roots and fibres that resist decomposition.

H9

Practically fully decomposed peat in which there is hardly any recognizable plant structure. When squeezed it is a fairly uniform paste.

H10

Completely decomposed peat with no discernible plant structure. When squeezed, all the wet peat escapes between the fingers.

B1

Dry peat

B2

Low moisture content

B3

Moderate moisture content

B4

High moisture content

B5

Very high moisture content

64

Note: The moisture regime of each peat sample is estimated using the above scale of 1-5 and symbol “B” (derived from Swedish blöthet = wetness). Farnham and Finney (1965) suggest that the most significant fault of many classification schemes is their failure to provide taxa, especially in the lower categories that lend themselves to mapping. There are many theoretical classification schemes which try to explain the origin of peat, but they do not lend themselves to the presentation of recognized classification units on maps. This is mainly because they lack the necessary information to recognize the taxa in the field by welldefined characteristics. A more pragmatic approach was suggested and this has since led to the development of a classification of organic soils, the essentials of which have been used by Soil Taxonomy. Soil Taxonomy, however, is concerned only with the classification of organic materials in a pedological sense so it does not solve the problem of classifying the environmental setting, which is essential for management purposes. The International Peat Society (IPS) established a working group for Peat and Peatland Classification in 1973 with the aim of developing a framework for a universal classification of virgin peat. The use of the word virgin suggests that the aim was not a classification which would be useful to agronomists. They are mainly concerned with the management and characteristics of peat which has been reclaimed and is no longer virgin. The IPS initiative led to the proposal of the scheme in Figure 10 at the 6th IPS Congress in 1980 in which three properties are used: botanical composition, degree of decomposition and the trophic status (nutrient richness) of the peat. According to Kivinen (1980), the system outlined in Figure 10 could be applied to most types of virgin peats in boreal and temperate regions and even those in the tropics. The framework, however, is only a start and requires further refinement and subdivisions according to local conditions and research requirements. The IPS proposal mainly deals with peat material rather than peatlands. Schwerdtfeger (1980) tried to rectify this shortcoming and suggested a system which would combine both the classification of peatlands or mires on the one hand, and the classification of organic soils on the other. Such a combined system would serve our needs, but, because of its complexity, an integrated system of this kind is difficult to develop on a global scale.

65

Figure 10 A proposed general classification scheme for peat

Source: Kivinen (1980)

66

5.5 Recommended Approach It is not within the scope of this Bulletin to discuss existing classifications. Ideally, however, a classification used as a tool for management should: i. Adequately describe and characterize the organic materials and the landscape to be reclaimed. ii. Supply sufficient information for producing resource management plans and allow the technical pros and cons of reclamation to be weighed against each other, thus leading to balanced decisions. iii. Allow insight into the limitations on reclamation so that any difficulties in soil and water management can be foreseen and adequately forestalled. There is at present no ideal classification. The basic information essential to developing such a system is lacking in most tropical and developing countries, where workers should therefore endeavour to collate and process all relevant data on organic soils and their environments. To this effect attention is drawn to the lists of essential data in Tables 5 and 6. In the meantime as developments go ahead it is essential that ways are found to serve present needs. Soil Taxonomy is one of several classification schemes of organic soils. It is the most comprehensive and its applied principles of classification appear to suit our purpose best. The legend to the Soil Map of the world (FAO/Unesco 1974) distinguishes only one Great Soil Group, the Histosols, which is divided into three subgroups - Eutric Histosols (those with high fertility), Dystric Histosols (those of low fertility) and the Gelic Histosols (those with permafrost). This system, though useful for indicating the occurrence and distribution of large expanses of organic soils on a regional basis, is not adequate for providing essential information for management. It is therefore not further discussed and we concentrate here on the Soil Taxonomy system.

5.6 Classification of Organic Soils According to Soil Taxonomy 5.6.1 Introduction 5.6.2 Fibrists 5.6.3 Hemists 5.6.4 Saprists 5.6.5 Folists 5.6.6 Further development of soil taxonomy for the Tropics

5.6.1 Introduction Organic soils are distinguished by Soil Taxonomy as the Order of Histosols (Gk. histos; tissue). Soils are classified as Histosols, if either more than half of the upper 80 cm of soil is organic, or if organic soil material of any thickness rests on rock or fragmental material having interstices filled with organic materials. The second criterion has been set up to permit the inclusion in the Histosols of shallow organic soils in uplands that have no water-table. These latter soils are outside the scope of this Bulletin. The general definition of Histosols requires adequate qualification of the terms organic and organic materials.

67

Organic materials These are defined as materials that, if saturated for long periods or are artificially drained, have 18 percent or more organic carbon if the mineral fraction contains more than 60 percent clay. If the mineral fraction contains no clay, the minimum content of organic carbon is 12 percent. With clay contents between zero and 60 percent soils should have proportional contents of organic carbon between 12 and 18 percent (for example, 30 percent clay is related to 15 percent organic carbon). Such soils are commonly termed mucks and peats. If never saturated with water for more than a few days, organic carbon content should be over 20 percent. Three basic kinds of organic soil materials are distinguished, namely the Fibric, Hemic and Sapric materials, according to the degree of composition of the original plant material. In the definition of these three types of materials fibre content is the main criterion and for this reason it is necessary to firstly define fibres. Fibres These are fragments of plant tissue, excluding live roots, large enough to be retained on a 100mesh sieve (openings 0.15 mm in diameter). The tissues should have retained recognizable cellular structure of the original plant. Sieving is done after dispersion with sodium hexametaphosphate. Fragments which are larger than 2 cm in cross-section, or in their smallest dimension, are called fibres only if they are decomposed enough to be crushed and shredded with the fingers. This excludes pieces of wood larger than 2 cm, which are regarded as coarse fragments comparable to gravel and stones in mineral soils. The degree of decomposition of organic materials is indicated by the content of fibres. In highly decomposed materials, fibres are almost absent. Slightly decomposed materials have more than 50 percent by volume, the remainder may be wood. Moderately decomposed materials have a high fibre content but they break down easily by rubbing and crushing. For this reason the percentage of fibres that do not break down when rubbed gives the most realistic field estimate of the degree of decomposition. Bulk density, an important physical characteristic particularly for management purposes, is more closely related to content of fibre after rubbing than in the undisturbed condition. In the field, an estimate is made by rubbing a small volume of wet material between thumb and fingers about ten times with firm pressure. The rubbed material is then moulded into a ball, broken and examined with a hand lens of times ten magnification. Many soils can be classified on fibre content solely by field examination but in marginal cases the test for solubility in sodium pyrophosphate can be used. Here, after rubbing in the laboratory, the materials are dispersed in sodium pyrophosphate and washed on a screen as described in Appendix 1. Where the results of the solubility and rubbing tests conflict the former take precedence. Having defined the term fibres it is possible to quantitatively describe the three forms of organic materials whose characteristics are summarized in Table 17.

68

Table 17 CHARACTERISTICS OF ORGANIC MATERIALS ACCORDING TO THEIR DEGREE OF DECOMPOSITION (source Soil Taxonomy) Fibric

Hemic 0.07-0.18

Sapric

Wet bulk density

<0.1

>0.2

Fibre content

2/3 vol. before rubbing 1/3-2/3 % vol. before 3/4 % vol. after rubbing rubbing

<1/3 vol. before rubbing

Saturated water content as percent of oven-dry material

850->3 000

450->850

<450

Colour

light yellowish brown or reddish brown

dark greyish brown to dark reddish brown

very dark grey to black

Fibric (L. fibra; fibre) These soil materials commonly have a bulk density of less than 0.1, an unrubbed fibre content exceeding two-thirds of the volume, and a water content, when saturated, ranging from about 850 percent to over 3 000 percent of weight of oven-dry material. Their colours are commonly light yellowish brown, dark brown or reddish brown. The colour of the sodium pyrophosphate extract on white chromatographic paper has values and chromas of 7/1, 7/2, 8/1, 8/2 or 8/3 (Munsell notations). Hemic (Gk. hemi; half) These soil materials are intermediate in degree of decomposition. Bulk density is commonly between 0.07 and 0.18 and the fibre content is normally between one-third and two-thirds of the volume before rubbing. Maximum water content when saturated ranges from about 450 to 850 percent. Sapric (Gk. sapros; rotten) These soil materials are the most highly decomposed. Bulk density is commonly 0.2 or more, and the fibre content averages less than one-third of the volume before rubbing. Maximum water content when saturated normally is less than 450 percent on the oven-dry basis. The colour of the sodium pyrophosphate extract on chromatographic paper is below or to the right of a line drawn to exclude blocks 5/1, 6/2 and 7/3 on the Munsell Colour Charts (Appendix 1). Apart from the three materials in Table 17, Soil Taxonomy distinguishes other soil horizons including limnic materials, which include both organic and inorganic materials. These were deposited in water either by precipitation, through the action of aquatic organisms such as algae and diatoms, or they are derived from underwater and floating aquatic plants. They include coprogenous earth (sedimentary peat), and inorganic diatomaceous earth, and marl. Their occurrence does not play a significant role in the classification of organic soils at high categorical level and is therefore not further discussed. Most occur at the interface between true organic deposits and mineral deposits. Soil Taxonomy also recognizes humilluvic materials, which is illuvial humus accumulating in the lower horizons of some acid organic soils where they have been drained and cultivated. The illuvial humus has a younger 14C age than the overlying organic soils. This material is of little importance for our purpose and is not discussed further. 69

Boelter (1969) illustrates convincingly that many important physical characteristics of peats such as water retention, water yield coefficient, and hydraulic conductivity are related to degree of decomposition measured by means of fibre content and bulk density. The distinction into Fibric, Hemic and Sapric materials has therefore been adopted as a very important criterion to subdivide Histosols into the suborders of Fibrists, Hemists and Saprists. The problem over what depth or thickness of layers peat of fibric, hemic or sapric nature are classified is addressed as follows. In general and for practical reasons an arbitrary control section has been established for classifying Histosols. It is either 130 cm or 160 cm thick, depending on the kind of material, provided that no rock, or rock-like material, thick layer of water or frozen soil occurs within those limits (the last criterion is of no relevance in tropical areas). In tropical situations a control section of 160 cm thickness is normally used. Layers of water may be thin or thick, ranging from a few centimetres to many metres. Water is taken as the base of the control section only if the water extends below a depth of 130 cm or 160 cm, depending on the kind of material above it. Such considerations are important for classifying floating organic materials. For more detailed information the reader is referred to the full text of the Soil Taxonomy. The control section is divided somewhat arbitrarily into three tiers, the surface, Subsurface and bottom tiers. i. The surface tier is the upper 60 cm if the material has a bulk density of less than 0.1, otherwise the surface tier is the top 30 cm, exclusive of surface litter or living mosses. If the surface is covered by mineral soil because of addition by men or natural causes such as flooding or volcanic eruptions the material is considered part of the surface tier, even if it is more than 30 cm thick and the depth is measured from the top of the mineral layer. ii. The subsurface tier is 60 cm thick, unless the control section ends in rock, or water is found within this depth. In either of these situations the subsurface tier extends from the base of the surface tier to the base of the control section. It includes any unconsolidated mineral layers that may be present within those depths. iii. The bottom tier is 40 cm thick unless the control section stops within the maximum span (160 cm), because of the presence of rock or water. For our purposes it is relevant also to characterize the nature of the soils below a depth of 160 cm, particularly if organic materials extend beyond this depth. Wastage initiated by drainage will eventually bring deeper layers within the control section. It should be remembered that Soil Taxonomy aims primarily at classifying the agronomic aspects and the current situation. We, however, are also interested in the feasibility of sustained drainage and the conditions which develop after reclamation. This requires knowledge of the nature of the peat layers at depth. The order of Histosols can now be properly characterized. As indicated the general rule is that, unless the surface tier has a bulk density of less than 0.1, a soil is classified as a Histosol if half or more of the upper 80 cm is organic, and that it is classed as a Histosol without regard to thickness of organic material if this rests on rock. If the bulk density is very low, less than 0.1, three-quarters or more of the upper 80 cm must be organic. Figure 11 outlines schematically the classification of Histosols down to the subgroup level. It includes only the subgroups found in the tropics.

5.6.2 Fibrists These materials mainly consist of weakly decomposed plant remains which are not destroyed by rubbing. Their botanical origin can be readily recognized and they consist either of partly decomposed wood or of remains of mosses, grasses, sedges and papyrus, or mixtures of both. In older American classifications they were called Bog Soils. Fibrists tend to have the lowest bulk density (less than 0.1) and lowest ash content of all the Histosols, though there are some exceptions, for example those found near volcanoes which have received falls of ash. 70

Not all Fibrists occur in the tropics. Those relevant to this study are Histosols that have been saturated with water for 6 months or more of the year or are artificially drained. Fibric soil materials are (i) dominant 1 in the organic part of the control section if there is a mineral layer (or layers) 40 cm or more thick whose upper boundary is in the subsurface or (ii) dominant in the subsurface tier if there is no continuous mineral layer 40 cm or more thick whose upper boundary is in that tier. They do not have a sulphuric horizon whose upper boundary is within 50 cm of the surface and do not have sulphidic materials within 1 m of the surface (see for definitions under Hemists). Only the Great Groups Tropofibrists and Medifibrists are found in the tropics. 1

Dominant; in this context, means the most abundant. If only two kinds of organic materials are present, the fibric materials occupy half or more of the volume. If there are both hemic and sapric materials as well as fibric, the fibric materials may occupy less than half of the volume but occupy a greater volume than either the hemic or sapric materials.

Tropofibrists These are Fibrists with an isomesic or warmer iso-temperature regime. They have a mean annual soil temperature of 8°C or higher and have greater than 5°C difference between the mean summer and mean winter soil temperatures at a depth of 30 cm. They occur in coastal mangrove swamps and other coastal swamps and in closed depressions of intertropical areas. If drained and cultivated, subsidence due to decomposition is rapid. If a sulphuric horizon occurs within 50 cm from the surface or sulphidic materials are found within 1 m depth the soils are excluded from the Tropofibrists, even though the organic materials may be dominantly fibric. They are excluded because the actual or potential acidity (acid sulphate conditions) is considered the most important property and Histosols with such materials at such depths are grouped in the suborder of Hemists. The central concept of the Typic subgroup of Tropofibrists is soil with thick, continuous, fibric organic materials. Thin layers of mineral material may restrict the movement of water drastically and where such layers occur the soils are regarded as intergrades to Fluvaquents. Soils with thick mineral layers (between 5 and 30 cm thick) within organic materials or with more than one thin layer of mineral material in the control section below the surface tier are also excluded from the Typic Tropofibrists and are placed in the Fluvaquentic subgroup. If mineral layers more than 30 cm thick occur with their upper boundary in the control section below the surface tier, the soils are placed in the Terric subgroup. The other subgroups of the Tropofibrists recognized are the Hemic, Hemic Terric, Hydric, Limnic, Lithic, Sapric and Sapric Terric subgroups. Their recognition is based on presence of hemic, and limnic materials and water within the control section. Medifibrists These are the Fibrists of mid-latitudes. Their temperature regime is mesic, thermic or hyperthermic. They have a mean annual soil temperature that is 8°C or higher and mean summer and mean winter temperatures at a depth of 30 cm that differ by 5°C or more. Their moisture regime is aquic 1 unless the soils have been drained. If these soils are drained and cultivated under the present technology the organic materials will decompose and disappear either slowly or rapidly, depending on management and the temperature. Eventually, within some decades Medifibrists, if drained and cultivated will be replaced by mineral soils. 1

Aquic moisture regime. The aquic (L. aqua; water) moisture regime is a reducing regime that is virtually free of dissolved oxygen because the soil is saturated by groundwater or by water of the capillary fringe. Some soil horizons, at times, are saturated with water while dissolved oxygen is present, either because the water is moving or because the environment is unfavourable for microorganisms, for example, if the temperature is less than 1°C such a regime is not considered aquic. For differentiation in the highest categories of soils that have an aquic regime, the whole soil must be saturated. 71

The central concept of the Typic Medifibrists is a soil that has thick, continuous fibric materials and little or no impedence to movement of water. Other subgroups of the Medifibrists are recognized using the same criteria as used for the Tropofibrists (Fig. 11). Fig. 11. Outline of the classification of Organic Soils (Histosols). Source Soil Taxonomy (Soil Survey Staff 1975) Notes *)

equivalent of 20% organic matter

**)

equivalent of 30% organic matter

***) TROPO - mean annual soil temp. (at 30 cm) of 8 degr. C. or more, less than 5 degr. C. difference between mean summer and mean winter soil temperatures MEDI

- mean annual soil temp. (at 30 cm) of greater than 8 degr. C., difference between mean summer and mean winter soil temperatures more than 5 degr. C.

****) All organic soils with sulfidic horizon within 50 cm surface in HEMISTS All organic soils with sulfuric materials within 1 m from surface in HEMISTS

5.6.3 Hemists These are primarily Histosols in which the organic materials have been decomposed enough that the botanical origin of as much as two-thirds of them cannot be readily determined or the fibres can be largely destroyed by rubbing between the fingers. The bulk density is usually between 0.1 and 0.2 g/cm3. The hemists have an aquic or peraquic 1 moisture regime, that is, groundwater is at or very close to the surface nearly all the time unless artificial drainage has been provided. The level of the groundwater may fluctuate but seldom drops more than a few centimetres below the surface tier. Histosols that have a sulphuric horizon or sulphidic materials are included with the Hemists without regard to the stage of decomposition of the organic materials. Hemists were called Bog soils in an older American classification system. 1

Very commonly, the level of groundwater fluctuates with the seasons. The level is highest in the rainy season, or in the autumn, winter or spring if cold weather virtually stops evapotranspiration. There are soils, however, in which the groundwater is always at or very close to surface. Examples are tidal marshes and closed, landlocked depressions fed by perennial streams. The moisture regime in these soils is called peraquic. Although the term is not used as a formative element for names of taxa, it is used in their descriptions as an aid to understanding their genesis. The Hemists within the tropics are Histosols saturated with water for 6 months or more of the year or they are artificially drained, and have one or more of the following features: i. Dominantly hemic soil materials in the organic part of the control section if a mineral layer (or layers) 40 cm or more thick has an upper boundary in the subsurface tier. ii. They have hemic soil materials dominant in the subsurface tier if there is no continuous mineral layer 40 cm or more thick that has its upper boundary in that tier. iii. They have a sulphuric horizon with its upper boundary within 50 cm of the surface or sulphidic materials within 1 m of the surface.

72

Sulphuric horizons and sulfidic materials are defined as follows: i. Sulphuric horizons are composed either of mineral or organic soil material that has both a pH less than 3.5 (1:1 in water) and jarosite mottles (the colour of fresh straw that has a hue of 2.5Y or yellower and chroma of 6 or more). They form as a result of artificial drainage and oxidation of sulphide-rich minerals or organic materials. Such horizons are highly toxic to plants and virtually free of living roots. ii. Sulphidic materials are waterlogged mineral or organic soil materials that contain 0.75 percent or more sulphur (dry weight), mostly in the form of sulphides and that have less than three times as much carbonate (CaCO 3 equivalent) as sulphur. Sulphidic materials accumulate in a soil that is permanently saturated, generally with brackish water. The sulphates in the water are biologically reduced to sulphides as the soil materials accumulate. Sulphidic materials are most common in coastal marshes near the mouths of rivers that carry non-calcareous sediments, but they may occur in fresh-water marshes if there is sulphur in the water. If the soil is drained, the sulphides oxidize and form sulphuric acid. The pH, which normally is near neutrality before drainage, may drop below 2. The acid reacts with the soil to form iron and aluminium sulphates. The iron sulphate, jarosite, segregates and forms the bright yellow mottles that characterize a sulphuric horizon. The transition from sulphidic materials to a sulphuric horizon normally requires a very few years. A sample of sulphidic materials, if air dried slowly in shade for about 2 months with occasional remoistening, becomes extremely acid. For quick identification in the field, a sample can be oxidized by boiling in concentrated H 2 O 2 and measuring the drop in pH. The suborder has seven groups of which only four are important in the tropics, the Tropohemists, the Medihemists, the Sulfohemists and Sulfihemists. Tropohemists Hemists of intertropical regions. They may occur in coastal swamps or in closed depressions. They have an isomesic or warmer temperature regime. The mean annual soil temperature is 8°C or higher and there is a difference of less than 5°C between the mean summer and mean winter soil temperatures at a depth of 30 cm. Soils with sulphidic materials or a sulphuric horizon are excluded and are placed in the other great groups (Sulfo- and Sulfihemists). The division of the Tropohemists into subgroups is based on similar criteria to those indicated for the Tropofibrists. - The hemic subgroups of the Tropofibrists are, however, replaced by fibric subgroups (Fig. 11). Medihemists Hemists of the mid-latitudes with temperature regimes characterized by a mean annual soil temperature of 8°C or higher and mean summer and mean winter soil temperature at 30 cm depth which differ by 5°C or more. Their moisture regimes are aquic unless the soils have been artificially drained. Their organic materials are derived from woody or herbaceous plants or mixtures of the two. If drained and cultivated the organic materials decompose and disappear to be replaced by the underlying mineral soils after some decades. Soils with a sulphuric horizon or a sulphidic horizon are excluded from this great group which is subdivided in similar fashion to the Medifibrists (Fig. 11).

73

Sulfihemists These are known as potentially acid sulphate soils (cat clays) that are dominantly organic. They have sulphidic materials within 1 m depth and have not been drained. They can have any fibre content, decomposition stage being overruled by the potential acid sulphate conditions. They are mainly found in coastal swamps, near the mouths of rivers or in deltas of rivers that carry sediments with a low content of carbonates. As yet the only subgroup recognized is the Typic Sulfihemists which are those acid sulphate soils which are dominantly organic. They have a sulphuric horizon developed as a consequence of draining sulphidic materials originally present in the organic deposits. They are extremely acid and toxic to most plants, colours are mostly nearly black and have straw coloured mottles of iron sulphate (jarosite) within 50 cm depth. They occur in similar topographic situations to the Sulfihemists, but are drained, either artificially or naturally if they occupy old coastal plains. They have a wide range of fibre content and most of them have an appreciable amount of mineral material within the control section. The presence of a sulphuric horizon is their key feature. Sulfohemists are rare and all so far identified have been classed as Typic Sulfohemists, no other subgroups have yet been recognized.

5.6.4 Saprists This suborder is characterized by almost completely decomposed plant remains, the botanical origin of which cannot be observed directly. The soils are usually black in colour and tend to have a bulk density of over 0.2 g/cm3. The groundwater-table tends to fluctuate within the soil. Aerobic decomposition of original materials is advanced. The Saprists were classified as Bog soils in the previous American classification. Saprists are Histosols that are either saturated with water for 6 months or more of the year, or have artificial drainage and satisfy the following: i. Sapric materials dominant in the organic part of the control section if mineral layer(s) 40 cm or more thick have an upper boundary in the subsurface tier. ii. Or have sapric materials dominant in the subsurface tier if no continuous mineral layer 40 cm or more thick has its upper boundary in that tier. iii. Have no sulphuric horizon with its upper boundary within the upper 50 cm or sulphidic materials within 1 m depth. The great groups relevant to our study are the Troposaprists and the Medisaprists. The basic difference between these is mainly temperature regime as already outlined for the Fibrists and the Hemists. Their mode of occurrence is very similar and their division into subgroups is based on similar criteria to those used for the Tropofibrists, Medifibrists and Hemists to which the reader is referred. Soil Taxonomy repeatedly indicates that the Hemists and Saprists eventually disappear when drained. This also happens to Fibrists, through the same processes of oxidation and subsidence, but decomposition is not as advanced as in the Hemists and Saprists. Because of temperature differences between Medi and Tropo great groups the latter tend to disappear fastest.

74

5.6.5 Folists The suborder of Folists are the more or less freely drained Histosols that consist of organic horizons generally indicated as litter, over rock or rock debris. In the earlier American classification they were classified as Lithosols. They are not further discussed here.

5.6.6 Further development of soil taxonomy for the Tropics The above outline of the classification of Histosols aims to stimulate use of the system in developing countries. It is by no means complete, however, so there is a need to expand upon it. The lower categories need particular attention for use in tropical countries. Detailed information on chemical characteristics, on the nature of the mineral part of the organic materials, for example texture, must be used for a further subdivision. Lucas (1982) mentions the use of parameters such as texture of mineral subsoil, presence of iron, kind of limnic material, depth of peat, soil reaction (pH) and soil temperature class for a separation at family level. In the USA, however, they use properties such as pH, temperature class, depth and the mineral soil texture within and/or below the organic soil layer at series level. It should be emphasized that, by definition, the Histosols are allowed to contain a considerable amount of mineral matter and for practical management purposes it is important to realize the difference between a soil with no mineral material and a soil with say 40 percent mineral matter. At a high level of classification such differences are not immediately obvious. Loss on ignition is therefore regarded as a key parameter which is easily analysed and which should be used as an important diagnostic feature in any system set up locally. Knowledge of both the depth and nature of peat beyond the 1.6 m control section and of the underlying material is essential to enable predictions of the behaviour of peat soils upon drainage and to estimate the lifespan of this wasting resource. Local systems should be geared to management requirements, including water control, so they should modify and supplement Soil Taxonomy.

5.7 The Classification of the Physical Environment There is as yet no classification that adequately characterizes the physical environment of organic soils as an aid to the development of appropriate management procedures and methods of water control. Moore and Bellamy (1974) devised a method using the concept of templates to describe and characterize wetlands or mires using the climate and geomorphological setting. They mainly dealt with temperate peats and environments unlike those found in the tropics. Although the methodology appears suited to our purpose, it needs to be adapted to tropical conditions. Based on experience in many tropical countries, mainly in South East Asia, we try here to show how such a system could be developed specifically for tropical conditions and for management planning. The following examples illustrate how a physiographic approach can bring some order to the many tropical ecosystems in which peats develop. They also give detailed insight into drainage needs because hydrological conditions can often be deduced from the physiographical setting. It is suggested that on a regional or national basis others can attempt to classify existing ecosystems using this approach. Figures 12 to 17 are examples in Indonesia, Malaysia, Thailand, the Philippines and Brazil.

75

Figure 12. Deltaic dome-shaped peatswamps Figure 13. Coastal dome-shaped basin peatswamps

Figure 14. Lagoonal peatswamps

76

Figure 15. Small inland valley peatswamps merging into basin swamps (coastal position)

77

Figure 16. Isolated peatswamps in major valleys

78

Figure 17. Atoll peat deposits (partly saline)

79

The physiography is presented by plans and cross-sections giving a three dimensional impression of the geomorphological units. Detailed information can be added when available. Diagrams of this kind are of considerable aid to planners not acquainted with the field situation. They enable them to visualize the reclamation problems involved. Finally, it is emphasized that basic investigations into peat deposits, their characterization and classification must be a concerted effort of the several technical and agricultural disciplines involved in both reclamation and subsequent use of the land. Without proper co-ordination and comprehension of the specific requirements of each discipline, work will be done in professional isolation. This frequently leads to failure and frustration.

80

6. AGRICULTURAL POTENTIAL 6.1 Introduction 6.2 General Suitability for Cropping 6.3 Land Capability and Crop Suitability Evaluation 6.4 Conclusions and Recommendations

6.1 Introduction Any assessment of potential agricultural use should first focus on several basic issues. Agriculture as considered here encompasses arable use (the growing of the widest possible range of annual crops), horticulture (perennial crops in general, and fruit trees in particular), pastural use (grassland and fodder crops) and silviculture (commercial growing of trees). An assessment of land use potential should take into account both the characteristics of the peat as a growing medium and the character of the peatswamps as a whole. In peat soils the improvement of drainage is usually the first step toward the creation of good growing conditions for crops. Artificial drainage, however, has several undesirable side-effects of which subsidence of the land surface is but one. These changes affect the physical and economical feasibility of peat reclamation on a sustained basis, and they therefore must be given prime attention in potential use assessment. It is thus necessary to distinguish between use potential for the years immediately after reclamation and the potential under conditions that develop eventually. A proper evaluation of the suitability of peats for a particular crop under fixed conditions first requires judgement on which characteristics of the peat and the peatswamps should be taken into account. The nature and range of any limitations for a certain use can then be assessed. Because of the dramatic changes that take place with peat wastage it is sensible to evaluate the potential use of the mineral soil beneath the organic materials taking into account the predicted environmental conditions after wastage. These can be markedly different from the original ones. This chapter deals largely with the process and methodology of evaluating peat soils and peatswamps and their suitability for various uses. Because of the complexity of the technical problems involved in reclamation and related management we have tried to divorce these aspects from the issues directly related to the evaluation of potential use. Technical problems of reclamation is dealt with separately in Chapter 7 and agricultural management is covered in Chapter 8.

6.2 General Suitability for Cropping There are diverse opinions on the suitability of peat soils for general agricultural use Coulter (1957) at one extreme, suggested that peat in peninsular Malaysia should be disposed of as rapidly as possible by removal, burning or deep drainage with the ultimate aim of using the underlying mineral subsoil for growing wet rice. This view is still heard in some quarters. Preservationists favour keeping most peatswamps in their natural state as nature reserves, because they are unique ecosystems with a specialized but threatened flora and fauna. Andriesse (1974) describing the tropical peats of South East Asia expresses the moderate compromise view that agriculture should only be allowed in areas which can be permanently drained at reasonable cost without endangering the environment. Other, generally deep peat areas are best left in their natural state for the possible development of silviculture.

81

The reclamation of peatswamps has always been a matter of some controversy. In the past agricultural development has avoided them for various reasons, usually disease risk, particularly malaria which kept the population from settling near the swamps. In the past, the main reason for draining peatswamps was probably to improve communications rather than to increase agricultural productivity. As a result of initial drainage, the land surface subsided and drainage conditions deteriorated. The environment became less healthy for the local populace necessitating rigorous reclamation. The history of the reclamation of the Pontion swamps, now the Agro Pontino in Italy follows this pattern. Development, which started in 312 B.C. with the construction of the Via Appia, was not completed until early this century when it finally became arable land and fit for permanent settlement. Another reason for draining swamps was turf cutting and use of peat as a source of energy. This took place in Europe starting in the Middle Ages becoming an important means of heating in towns until it was replaced by coal and oil during the 19th and 20th centuries. Peat is still used today in many countries but mainly for fuelling electricity power plants. Because of its relative importance as an alternative energy source in some developing countries the use of peat materials for energy is dealt with specially in Chapter 9. The agricultural use of tropical peat is commonly viewed with great scepticism. Pons and Driessen (1975) summarize the findings and opinions of most research workers in South East Asia. They express the view that the poor chemical and physical properties of oligotrophic lowland peat soils in South East Asia indicate a very low suitability for any agricultural use. Traditional reclamation disturbs the existing equilibrium which leads to rapid chemical exhaustion of the soil and to strongly increased compaction and decomposition of the peat. The deep, oligotrophic lowland peats produce most biomass if left under forest vegetation, and if managed carefully, exploitation of the forests is possible; a view endorsed by Andriesse (1974). They a brogue that modern agriculture is only possible with uneconomical capital inputs. In many countries, however, peat soils are more highly rated than mineral soil as a medium for intensive cropping. This is particularly so for vegetable growing (Cassidy 1968). Stephens (1969), reviewing the drainage problems of peats in Florida, explains the apparent contradiction of very low suitability on the one hand versus high suitability on the other as follows: “this peat, when drained, properly fertilized, and augmented by minor elements, breaks down into an excellent soil. Today, these soils, together with the mucks, make up one of the richest agricultural regions on earth”. This indicates that after various conditions have been met peat can become an excellent medium for plant growth. The difficulties arise in the realization of the conditions required. Improvement of drainage appears feasible at first sight, but once oxidation and subsidence have started, keeping drainage at satisfactory levels to match the rate of subsidence can become a technical and financial nightmare. For this reason many peat researchers take the view that before starting to drain, think twice. Nevertheless, in many countries peatswamps form a substantial land resource to which politicians and development planners alike are attracted because of several positive aspects, for example; the location, often along major rivers or in deltas; the flat nature of the land, presenting no erosion hazard; the feasibility of irrigation; and the low population density. Pressure is greatest where population growth leads to demands to open up new agricultural land. In such areas interest is often directed to the vast tracts of swampy lands, hitherto untouched. If they are near large population centres offering a ready market for vegetables and fruit, the reclamation of peaty swamps is a lucrative alternative to hauling truck crops from remote areas. These latter areas may have better and more sustained conditions for the growing of the crops, but they are economically less attractive. When assessing agricultural suitability the sustainable economic feasibility should be taken fully into account.

82

Land evaluations based on economic considerations are by nature short-lived because the conditions influencing commodity prices and the farmer’s costs can change rapidly. The latter can be to some degree unpredictable if sustained reclamation costs have to be covered by farmers. There are, however, conditions which would make the agricultural use and reclamation of peatswamps unavoidable and sometimes even desirable. Full understanding of the limitations can help to limit unrealistic expectations. In this way failure can possibly be avoided. The following sections outline procedures for assessing the agricultural potential of peats.

6.3 Land Capability and Crop Suitability Evaluation 6.3.1 Introduction 6.3.2 The initial survey

6.3.1 Introduction A proper initial survey is the only sound base from which the future use of a peatswamp can be evaluated. Data supplied by such a survey should give indications on the immediate limitations for the proposed agricultural use. These can then be checked against crop requirements. Any proposals for improvement should be the considered outcome of such a matching procedure. Thereafter, the socio-economic consequences and feasibility of the intended use, with or without improvements, can be properly assessed. This procedure is more or less the same as outlined in an FAO Bulletin (FAO 1983). Both parallel and two-stage approaches can be used. In the first the initial survey covers simultaneously the physical conditions of peat and peatswamp and relevant socio-economic factors. In the second approach the physical landscape features are studied initially followed by socio-economic studies in a subsequent phase. The first approach has the advantage of integration of effort and gives feedback from an interchange of information between the various disciplines involved. It is, however, costly and difficult to organize, so in many cases it is probably more efficient to evaluate the physical situation first and thereafter consider the various technical alternatives which can then be evaluated in their socio-economic context. The suggestion is made that an initial rapid appraisal is made before deciding to proceed with more detailed studies.

6.3.2 The initial survey A clear distinction must be made between the agricultural value of the organic materials, and the suitability or potential of the peatswamp for agricultural development. Severe wetness is commonly the first serious limitation to cropping in swampland, and drainage is a prerequisite for most agricultural developments. Appraisal of the potential for the provision of adequate drainage is a priority. In this connection the term Reclamation Potential is introduced to parallel the term Agricultural Potential which is used in the restricted sense of the agricultural suitability of the peat materials only. The initial survey should, as far as possible, assess both potentials. The following survey procedures are suggested. Organization The area to be studied should firstly be reconnoitered using a scale between 1:50 000 and 1:100 000 depending on its size. Figure 18 illustrates how such a quick survey can be accomplished along transects. The position of the transects depends on the configuration and type of the peatswamps. Satellite images or air-photographs, if available, give important clues to configuration, vegetation and risk of flooding. The extent of the latter may vary with the season. 83

Surveying is helped by easy access so the best season should be chosen for swamp investigations. The end of the driest season is usually the best time. It is always worth checking the extent of flooding of the peat at the rainy season when the highest local floods are expected. If it is not possible to visit the area at this time indicators or signs of flooding should be used later. Vegetation can be a great help, by the distinct marks left on trees (Plate 2) indicating the highest water levels during the wet season. These often remain clearly visible during the following dry season. If air-photographs are not available contoured maps are needed to supply the basic topographic information for the survey.

84

Plate 2. Flood levels from the wet season remain visible on the tree trunks during the dry season, South Irian Barat (Indonesia) Figure 18. Location of observation lines in initial field surveys of peatswamps

Survey parameters

85

The initial survey should concentrate on the following aspects: Nature of peat a. Fibric, mesic or sapric (decomposition stage). b. Woody or non-woody. c. Mineral soil component (quantity, layered, non-layered or dispersed). Depth of peat This is best recorded using locally decided depth classes. These, for example, could be 0-50 cm (very shallow), 50-100 cm (shallow), 100-150 cm (moderately deep), 150-200 cm (deep), >200 cm (very deep). Initial subsidence after reclamation might be as much as 50 cm, leaving in the case of shallow peat only a few centimetres of peat after initial drainage. The quantity of the mineral component also influences the thickness of the peat soil after subsidence. Nature of underlying materials Texture (clays, loams or sands) and character (fertile, infertile, marine with shells). Presence of sulphidic materials a. In the organic deposits. b. In the underlying mineral soil (potential acid sulphate conditions). Salinity of groundwater Levels of conductivity measured with a normal electric conductivity meter. Depth of groundwater Date of measurement should be carefully noted, because of seasonal fluctuation.

Sampling Samples of the organic and mineral materials should be taken at various selected depths and at various distances from the main drainage channels or the coast. They should be taken at field moisture content in air-tight containers or plastic bags for subsequent laboratory analysis. The range of possible analyses is large (Table 5) but for an initial appraisal of fertility the following should suffice: - loss on ignition, - pH, - texture (organic and mineral component), - test on presence of pyrite (drying/wetting method on field moist samples or chemical methods such as total oxidizable sulphur), - nitrogen content percent, - carbon content percent, - bulk density (field condition, undisturbed), - cation exchange capacity (CEC), 86

- exchangeable cations Ca, Mg, K, Na, H and Al, - available phosphorus. Topographic information The topographic data to be collected along the transects in the initial survey are as follows: Levels of surface configuration These should be related to a benchmark. They can then be correlated with known flood and mean water levels in the main drainage channels, and in some circumstances with mean sea level. Data on hydraulic conductivity Vertical and horizontal hydraulic conductivities are useful determinations but they are not often readily available. Crude information can be obtained relatively easily by installing a drain and measuring the water-table depth at increasing distances (piezometer method). Subsidence Where possible any information should be obtained from local inhabitants on the rate of subsidence after the installation of drains, however rudimentary. Flooding and inundations Settlers near the swamps are often a good source of information on incidence, size and persistence of flooding. Agricultural suitability rating The results of the initial survey can be used to evaluate the potential suitability of the land for various agricultural uses. In this process it is first necessary to rate the various soil characteristics or limitations recognized in the district. Favourable and unfavourable characteristics and qualities are evaluated by either a scoring or point system (the quantitative approach) or by the use of descriptive terms such as good, moderate, bad and serious (the qualitative approach). Many countries have developed such land capability rating systems mostly for mineral soils. Most systems are based on the presence or absence, severity and number of limitations on the husbandry of selected crops. Some suitability ratings also take into account the type of management and farming skills, whether, for example, traditional, improved traditional or with input of modern technology. Soil limitations can also be grouped as permanent or non-permanent depending whether they can be removed or overcome by management. Fertility and wetness are examples of non-permanent limitations; soil depth or texture of permanent ones. Because of the specific characteristics of organic soils they need specially designed capability or suitability systems. Table 18 outlines such a system developed for the oligotrophic lowland peats of Sarawak which can be regarded as being representative of peat soils in South East Asia. The capability classes in Table 18a are based on the number and severity of soil limitations for general cropping purposes (Table 18b). The ratings shown in this table are based on local experience and are expressed in qualitative terms (minor to very serious). The system serves as an example of how to recognize and interpret the various limitations of organic materials and how to use these assessments to arrive at a proper rating system for a selection of crops. 87

A general assessment of capability classes for agricultural purposes is not sufficiently detailed for individual crops or a range of crops. For this, it is necessary to match the capability class assigned to each soil type to the specific soil requirements of the particular crop or range of crops to be established. The specific soil conditions taken into account should be those necessary to give a satisfactory and sustained yield performance. Appendix 3 gives tables indicating soil requirements for a wide range of common crops in South East Asia and in Sarawak in particular. The matching or correlation of soil capability class with the indicated specific requirements gives a number of suitability ratings for relevant crops or ranges of crops as shown in Table 19. Land is either unsuitable (U), conditionally suitable (C - conditions are given), marginally suitable (M) or suitable (S). The reason for placing soils in the recognized suitability classes is indicated by letter symbols which are also used for the capability subclasses (see Table 18b). Table 18 ASSESSMENT OF CAPABILITY CLASSES FOR ORGANIC SOILS BASED ON LIMITATIONS TO CROP SUITABILITY AS USED IN SARAWAK (MALAYSIA) (source Maas et al. 1979)

a - Number and severity of limitations for each capability class

Class

Number of limitations Minor

Moderate

Serious

Very serious

1

0-1

0

0

0

2

2-3

1 or its equivalent

0

0

3

>4

2-3 or their equivalent

1 or its equivalent

0

4

-

4

2-3 or their equivalent

1

5

-

-

>4

>1

b - Limitations to crop suitability on organic soils Degree of limitation Symbol

Type of limitation None 1

Minor

Moderate

Serious

Very serious

a

Depth to sulphidic layer (cm)

>100

75-100

50-75

-

-

f

Fertility of the organic layer

Medium (loamy 2 muck)

-

-

Very low (peat or sandy muck)

-

g

Depth to groundwater-table (cm)

-

-

30-60

0-30

-

-

30-60

>100

-

natural

drained 60-100

h

Degree of decomposition

Hemicsapric

-

-

Fibric

-

i

Inundation hazard (frequency and duration)

None

Infrequent, short

Frequent, short

Infrequent, long

Frequent and long or submerged

n

Nature (texture) of mineral subsoil at 50-100 cm depth

Fine loamy to clayey

o

Depth of organic layer (cm)

-

-

50-100

>100

-

s

Salinity of groundwater (mhos/cm)

<1 000

-

-

1 000-4 000

>4000

1 2

Sandy to coarse loamy

Depth after reclamation; allow 25 cm more for subsidence of virgin organic soils. The clay content of the mineral component must be greater than 18%. 88

A somewhat different approach in peatland appraisal and estimation of suitability is used in the USA. Here the Soil Conservation Service has developed guidelines to be used when organic soils are considered for forestry or agriculture. In contrast with the system developed and used in Sarawak, which is basically a qualitative system because of the lack of quantitative cropperformance data, the USA uses a penalty system for recognized limitations. In this system the higher the score, the poorer the suitability. As in the Sarawak system, location, farm size and sociological influences are not considered; thus in both cases there is an emphasis on physical conditions of the land. Table 20 outlining the American system, shows that essentially both systems recognize the same limitations for crop growth, the differences Table 19 LAND AND CROP SUITABILITY CORRELATION AS USED FOR PEAT SOILS IN SARAWAK (MALAYSIA) (source Maas et al. 1979) 1. = Wetland rice

8. = Sugar cane

15. = Coffee

2. = Upland rice

9. = Fodder crops

16. = Fruit trees

3. = Maize, sorghum

10. = Forage crops

17. = Coconut

4. = Soya bean, vegetables

11. = Pineapple

18. = Cashew

5. = Groundnut, tapioca

12. = Cocoa

19. = Sago

6. = Watermelon

13. = Oil palm

20. = Rubber

7. = Banana

14. = Pepper, papaya

* Letters refer to type of limitations (subclass) given in Table 18. ** S

- Suitable (minor and major soil conservation measures are required for slopes of 12-25° and 25-33° respectively).

(S)

- Suitable for small-holder and subsistence farming only.

M

- Marginally suitable (this is mainly deemed to reflect the low nutrient availability thereby restricting productive agriculture).

C

- Conditional on:

1. non-flood season (e.g. annual on flood-prone areas); 2. feasibility of flood irrigation; 3. tolerant or suitable cultivars (e.g. padi on weakly saline soils); 4. slightly improved drainage (e.g. shallow rooting crops on shallow peats); or 5. permanently saturated condition (e.g. wetland rice on sulphidic soils).

C4M - Conditionally marginal, the number in the centre stipulates the condition (see C). U

- Unsuitable. differences being mainly in the rating of those limitations.

89

It should again be emphasized that the examples given deal only with the agricultural potential or suitability of the peat as a growing medium in field conditions. They do not cover socio-economic factors, nor do they pay attention to possible weed and soil-borne pest problems. It is assumed in the examples that drainage can be provided. The Sarawak system, in particular, is far from being an evaluation on which the economic feasibility of crop production can be assessed. The USA system being based on long-term experience and quantitative analysis of crop production on the various types of peats, could serve a useful purpose locally elsewhere. There are often, however, big differences in conditions in most developing countries so only the broad outlines of the system can be copied. The detailed ratings should be thoroughly adapted to local conditions. Table 20 MANAGEMENT SUITABILITY FOR SPECIFIC CROPS ON ORGANIC SOILS IN THE LAKE STATES OF NORTH-EAST, USA (source Lucas 1982) Penalty rating for extended use Physical feature Corn Pasture

Cool season carrots, celery beets, onions

Short season lettuce, radish, cabbage, spinach

Sod

Growing Degree days above 50° F.

Above 3 000

0

0

0

0

0

2200-3000

20

10

10

10

10

Below 2 200

50

20

20

20

20

Above 130 cm

0

0

0

0

0

90-130 cm

5

5

10

10

10

40-90 cm

10

10

25

25

25

Loamy

0

0

0

0

0

Clayey

5

5

5

5

10

Sandy

10

10

10

10

10

Thickness of organic material

Underlying material 40-127 cm depth

90

Coprogenous

20

20

20

20

20

Marly

30

15

15

15

15

Rock

50

30

50

50

50

0

0

0

0

0

Peat

20

20

20

20

30

Marl

40

40

40

40

40

None

0

0

0

0

0

Slight

20

5

20

15

15

Frequent

70

20

70

50

50

0-1%

0

0

0

0

0

1-10%

5

0

10

10

20

10-25%

10

5

10

20

50

Above 25%

25

10

40

40 100

Surface texture 0-40 cm depth

Muck, mucky peat

Flooding during growing season

Wood fragments >10 cm in diameter within 127 cm depth

Soil reaction (pH) in 0.01 M CaCl 2 (0-40 cm depth)

91

Below 4.0

20

20

20

20

20

4.0-5.0

10

10

10

10

10

5.0-7.0

0

0

0

0

0

10

5

10

10

10

75

75

75

75

75

0-4

0

0

0

0

0

4-8

20

20

20

20

20

8-16

50

50

50

50

50

Above 16

75

75

75

75

75

Above 7.0

Acid sulphate below pH 3.5

Salinity (mmhos/cm)

Total penalty

score and suitability group

0-15

No limitations

20-30

Minor limitations

35-45

Moderate limitations

50-60

Severe limitations (high reclamation costs)

65-80

Severe limitations (forage only)

85-120

Indigenous crops only

Above 120

Not advisable for agriculture

92

It is probable that the greatest obstacle to the economic evaluation of peat reclamation for cropping is the correct assessment of the feasibility of drainage on a sustainable basis. In the developed countries the reasons for draining swampland have often been multipurpose and reclamation has been a long historical process of learning and adjustment. Mistakes were made and lessons learnt. In the developing countries the decision-making process is frequently geared by different motives. Here rapid changes in socio-economic conditions have resulted in a demand for land and have needed quick action. Much of the drainage of peatlands in the developed countries would never have been attempted if the consequences could have been predicted. Reclamation of similar areas in the developing world can therefore learn much from their experience accumulated over the centuries. An assessment of the Reclamation Potential, which for historical reasons has not played much of a role in the developed countries except during the last 50 years, should play an important role in developing countries if mistakes are to be avoided. As indicated reclamation potential should be assessed separately, and be based on different parameters from those used for the assessment of the Agricultural Potential. Reclamation Potential An assessment of the reclamation potential should try to answer the following questions: a. Is it possible to drain the swamp by gravity? If so, what will be the maximum depth at which adequate drainage can be provided without having to resort to costly pumping? The sustainability of adequate drainage is strongly related to the present elevation of the land (peat) surface, the rate of subsidence of the surface after drainage, and the elevation of the underlying mineral deposits or rocks. The data collected on these levels in the initial survey should provide sufficient insight. In the case where the level of the underlying mineral material is above the level of the main drainage outlet, it is possible to drain the peatswamp beyond the stage where the peat has completely disappeared. In cases where the mineral subsoil lies below the level of the main drainage outlet, gravity drainage must eventually be replaced by pumping or the land must be abandoned (Fig. 8). b. What is the expected life time of agricultural land in the reclaimed area? Life expectancy of the agricultural use of the reclaimed peat depends on the nature of the peat (including the proportion of mineral material) and its likely rate of oxidation and subsidence. These factors are in turn related to climate (temperature) and depth of drainage. For example, much of the present area of organic soils in the upper Everglades of Florida (USA) will have become too shallow, as a result of subsidence, to support profitable agriculture by the turn of the century. This will come about approximately 75 years after drainage to an original depth of about 3 metres. The overriding problem of subsidence is discussed in detail in Chapter 7. In the assessment of reclamation potential the rate of subsidence features strongly as a negative factor. c. What is the danger of infiltration by saline water in surface and groundwater? The possibility of infiltration of saline water is an important factor in assessment of coastal freshwater peatswamps. Here, where the main drainage outlets are tidal, artificial drainage and accompanying subsidence are a hazard.

93

d. What are the prospects of continuing agricultural production on the non-peaty subsoils once the peat cover has disappeared? To answer this question the nature of the underlying material must be known and taken into account and it should also be assessed to what extent agricultural production can continue. Conditions may have changed so much by then that gravity drainage, for example, might no longer be possible and will have to be replaced by a polder system. e. What is the incidence, magnitude and nature of flooding in the area to be reclaimed? The risks of flooding are best assessed when the nearby rivers are in spate. This could result from high rainfall upstream, from local rainfall or from a combination of the two. Sustained drainage of swamps is not possible without the installation of dykes where the flood levels of main drainage outlets are frequently high. The economic evaluation of measures to be taken depends greatly on the frequency and size of the floods. The author has noted in several schemes a disproportion between the effort spent on draining peatland and the attention given to flood control. This is in many cases so because a swampy area can be partly drained by private enterprise but flood control measures are beyond the scope of individual farmers. The reclamation of peatswamps is not just a matter to be decided on the strength of the agricultural suitability and the reclamation potential of the area directly involved. Reclamation means drainage, the effects of which are felt in the land around. Unwanted side-effects in fringe areas may include changes in water regime causing flooding or changes in salinity from fresh to brackish water or the reverse in former salt water ecosystems (mangroves). These changes may in turn influence economic activities such as fishing, which might upset the economic feasibility of the whole reclamation effort. Such considerations are discussed in detail in Chapter 10.

6.4 Conclusions and Recommendations There are many limitations to the agricultural use of peat soils. Added to these are the problems caused by reclamation of which the subsidence initiated by drainage, a prerequisite for most agricultural enterprises, is perhaps the most serious. Each peatswamp should be carefully surveyed to collect basic data for a land use evaluation. Because of the complexity of the reclamation problems and the ever-changing characteristics of the peat after reclamation, an economic evaluation of reclamation for agriculture is difficult. Much depends on the scale of the proposed operation, its size, location and the specific nature of the swamp. Each project needs an individual approach. Some broad general guidelines can be given. i. No peatswamp should be artificially drained before a careful assessment is made of the benefits and disadvantages based on a well planned initial investigation. ii. Piece-meal development of large peatswamps should be avoided if possible. Spontaneous settlement followed by unorganized reclamation and drainage often results in greater future problems than solved in the short term by reclamation.

94

iii. The main options for potential use should be studied carefully. These could be: - To retain the present natural conditions which might be primary forest. Forest products could be exploited on a small scale with a policy of silvicultural measures to ensure sustained production. - Use for agricultural purposes after improvement involving drainage, and possibly flood control. There are various possibilities for agriculture including shallow drainage with an adapted cropping system and choice of crops (annual and perennial), moderate drainage to allow a wider range of crops, and rigorous deep drainage. Shallow drainage avoids the risk of rapid subsidence and enhances the life span of agricultural use, moderate drainage gives more kinds of use choices but faster subsidence. It costs more to maintain drainage and agricultural life expectancy is shorter. Deep drainage leads to rapid peat wastage and is only recommended if the underlying soil is of very high quality. There is a vast array of crops which can be grown profitably on peat soils, the choice is decided mainly by climate and marketability. Growth performance depends very much on the chemical fertility and physical conditions for growth. There is no reason why most crops cannot be grown on peats given the required improvements. Here the economic feasibility plays the most important role, though technical problems such as the instability of top-heavy perennial tree crops remain a limitation. This is discussed in detail in Chapter 8. It should be carefully considered when making decisions that peat soils reclaimed at high costs will ultimately disappear leaving a changed landscape. The changes can be drastic, sometimes forming lakes. Once the decision is made to proceed with development many potential problems can be forestalled and prevented by adopting correct management procedures in both reclamation and in the subsequent agricultural enterprises. Management aspects are discussed in the following chapters.

95

7. RECLAMATION PROBLEMS 7.1 Introduction 7.2 Initial Problems in Peat Reclamation 7.3 Permanent Constraints in Peat Reclamation 7.4 Water-table Management

7.1 Introduction The reclamation of peatswamps should be multidisciplinary but in practice this is often not the case. The data collection and research described in previous chapters dealing with the formation, characteristics, classification and agricultural potential of peatswamps is carried out by biologists, chemists, geographers and pedologists. The reclamation of peatswamps, however, traditionally involves civil and/or technical engineers and hydrologists. The agricultural activities following and accompanying reclamation are then again in the sphere of the agricultural scientists. Last but not least it is the farmer who takes decisions at farm level and often, particularly in developing countries, carries the burden of the initial efforts in swamp reclamation. The constraints in reclaiming peatswamps are therefore often experienced by those who are least scientifically equipped to understand the nature and cause of the problems. It is the nature and case of reclamation problems that are discussed in this chapter and frequent reference is made to the background information given in Chapters 1-6. For practical reasons, the problems involved in the reclamation of peatswamps are divided into: temporary, mainly the initial problems of land clearing and land preparation, and permanent or recurring problems. These can be subdivided into social and technical problems of land and water management, and agronomic problems related to cropping. This chapter is devoted more to the recurrent or permanent constraints which are very difficult or impossible to remedy, rather than to the initial temporary problems which are often of a technical or economical nature and more easy to overcome. Emphasis is on the permanent constraints of a social and technical nature, whereas problems related to cropping will be specifically dealt with in Chapter 8.

7.2 Initial Problems in Peat Reclamation 7.2.1 Initial drainage 7.2.2 Clearing 7.2.3 Burning 7.2.4 Organization

7.2.1 Initial drainage Commonly the first phase of reclamation is drainage to reduce the periods of waterlogging and hence improve the soil bearing strength. This is necessary to improve accessibility, particularly if heavy equipment is to be used in the subsequent provision of access roads, land clearance, installation of major drainage canals and land preparation. Although the present day reclamation of peats in temperate regions utilizes machinery, in tropical areas it is still often very difficult to get heavy equipment to peatswamps. Here most operations, particularly the initial ones, have to be carried out by hand. 96

Irrespective of whether the initial drainage is done by machine or hand, the nature of the peat and the vegetation it carries are the main problems to be taken into account. If the peat is very woody, operations will be slow and costly. In the lowland peat of Borneo, woody peat (with large undecomposed logs) took 10 times the amount of labour to dig drains than relatively non-woody peat (Plate 3). It is therefore important to know the content, nature and depths of any woody components prior to starting reclamation (Chapter 6, Initial survey). The initial installation of drains at strategic positions allows access for equipment either by temporary road or narrow gauge railway. The latter is often also used for timber extraction in tropical lowland peats without the provision of any land drainage. Because of this flexibility in use, it can be installed relatively quickly and cheaply, where it is most needed (Plate 4). Peat has a low to very low surface bearing strength of between 0 and 40 kPa. This is too low for even light modern farm machinery which has a ground pressure of about 50 kPa. Lighter machines bog down because of high rolling resistance and slip. An alternative to narrow gauge rail tracks are roads with a raft base. Thick branches or small logs laid side by side on the low hummocky relief of the peat surface provide a buoyant base on which an earth track can be established. These provisional paths are often important in any initial reclamation by providing access for both labour and equipment. Without a raft base, dumping earth onto peat has little effect, particularly if mineral subsoil is only found at considerable depth. Roads constructed without such rafts will be short-lived and can disappear overnight because of sinking. Plate 3. Large fragments in peat increase the labour costs of digging drainage channels. Central Kalimantan, Indonesia Within the framework of this Bulletin it is neither possible to give detailed designs for structural works in peatswamps, nor is it the intention to give engineering specifications for the required drainage layout, beyond some general information of practical importance. As this chapter discusses problems of reclamation, routine water control measures are dealt with in Chapter 8. Some remarks should however be made on specific problems of making ditches in organic materials. Ditches in peat soils erode rapidly when the velocity of drainage water is greater than about 1.50 m per second. This value varies slightly depending on the nature of peat; fibric materials behaving differently from more sapric materials. Unfortunately there are no values for tropical peats. Gradients of ditches for gravity drainage should not be over 3 ‰, again this value has not been checked empirically. Erosion of ditch sides can be a severe problem. They preferably should be of a 1:1 design to enhance stability. But again the nature of the peat and size of the canal or ditch are important parameters, for example narrow lateral ditches with vertical sides up to 90-120 cm deep are satisfactory in fibric materials but these measurements are unsuited to the more unstable aquatic organic materials, even when containing large amounts of wood (Plate 5). The stability of ditch banks and the protection of slopes can be improved by growing shrubs, low trees or deep rooting grass which will not grow under water and so not choke the ditches. Tall, topheavy trees are unsuited because of problems of poor anchorage in peat. The problems of making ditches and preventing leakage through their sides when the outside water- table is higher than the water level in the drains are inherent in porous peats. They are mentioned here without further discussion as are the problems caused when making slopes and ditches by dumping relatively heavy, mineral soil material, taken from below the peat, on the soft spongy peat surface. These are problems of soil mechanics and hence outside the scope of this Bulletin.

97

Plate 4. Narrow gauge railway used for logging in large peatswamp in Sumatra, Indonesia, with author engaged in initial field survey Plate 5. Eroding main drain in deep woody peat, West Kalimantan, Indonesia

7.2.2 Clearing The clearing of vegetation is often difficult, and is another obstacle to reclamation. Unstable, wet surfaces with low bearing strengths make the use of bulldozers or tractors with winches impossible. Vegetation in tropical countries is commonly dominated by trees or thick brush (Plates 6 and 7), which is difficult to remove by hand. Clearing should be carefully programmed to avoid the clearance of too large an area at any one time as once drainage has been provided and vegetation removed the peat will start to decompose. Further, as the surface of peat dries the fire hazard increases. Clearance and drainage should never embrace more land than can be put to immediate use. Clearing involves the removal of trees, stumps and roots. Where large trees are present their stumps are very difficult to remove. The piling up and burning of cleared vegetation should be avoided but if necessary should only be done under carefully controlled conditions as a fire within the peat, once started, can carry on for months and may last a full dry season. Because of the large range of peat characteristics and the variety of conditions under which the swamps are reclaimed it is impossible to give full details of equipment that can be used. In developed areas, where the peat is drained and of high trafficability (bearing strength) and the vegetation is characterized by trees or shrubs of less than 5 cm diameter, tractors fitted with a front mounted bulldozer blade can be used to push down the vegetation. The land can then be turned over with a breaking plough (Lucas 1982). Generally, in developing countries the clearing and removal of vegetation is done entirely by hand. In countries with a pronounced dry season, the danger of starting fires in the peat necessitates the removal of coarse vegetation debris by stockpiling the stumps and leaving them to rot for a number of years. During a recent reclamation project in Brazil, the stockpiled wood was gradually removed for firewood by local settlers living on the periphery of the swamp. Such a practical use might be recommended where relatively small interior valleys are reclaimed by private companies and there is a shortage of firewood in the neighbouring already settled hills (Plate 8). Plate 6. Primary forest vegetation of deep peat with logging track, West Kalimantan, Indonesia Plate 7. Bush vegetation of deep peat with initial clearing for drainage, Brazil. Plate 8. Piles of wood from the original vegetation left to decay in a lagoonal peat reclaimed for sugar cane, Brazil.

98

7.2.3 Burning Frequently surplus vegetation is disposed of by burning. This is traditional practice in peat reclamation by the local population in South East Asia. Apart from being a rapid way of removing the cut vegetation, the ashes improve the fertility of the peat in the initial years of cropping. In some localities, it also quickly disposes of the surface fibric layers, which are unsuitable for tillage. However, the fertilizing effect is quickly lost and common practice is either a reburn of peat or abandoning the area following a shifting cultivation pattern. Such frequent burns can lead to rapid lowering of the peat surface, but more directly, it can lead to intensive peat fires when not properly controlled. Usually, the local population are adept at preventing this but the danger lies with nontraditional farmers. These are commonly unacquainted with the local conditions and by copying the methods of the locals are unaware of making reclamation errors and thus create havoc by uncontrolled burns and too deep drainage. Controlling peat fires is extremely difficult. One method is to dig a drain around the fire down to the wet soil but compacting the peat by mechanical means is more effective. The use of high-pressure water, if available, is satisfactory when the fire is small. The removal of wood and roots, particularly if present in great quantities (Plate 9) is a time consuming and costly activity. Lucas (1982) indicates that the cost of clearing a woodland site may be 30 times more than the cost of a grass covered site. Most tropical peats are forested in their natural state and in some instances clearance may be uneconomic.

7.2.4 Organization It is general practice in South East Asian countries that the major drainage system for the initial phase of reclamation is developed by a Government Agency such as the Ministry of Public Works or a Drainage and Irrigation Department. Subsequent installation of field drainage systems and land clearance is accomplished by the settlers. These activities should be carried out according to a prepared blueprint under strict rules and regulations. Rapid settlement of peatswamps lacking a co-ordinated effort and planning can lead to disastrous results. Whereas Government-sponsored reclamation projects sometimes fail because of the lack of or only belated recognition of the erratic behaviour of peatswamps when reclaimed, the opposite may be experienced when autochthonous settlers, by tradition locally knowledgeable of the behaviour of their peats, initiate reclamations with success. The success of the reclamations by the local population is often because no use is made of machines and only shallow drainage is practised. Further, most reclamation is carried out on shallow peat bordering main rivers because here the problems are less than on deep peat. The behaviour of peat after drainage, and the problems this creates, is discussed in the following section.

7.3 Permanent Constraints in Peat Reclamation 7.3.1 Subsidence 7.3.2 Cultivation practices

7.3.1 Subsidence Subsidence or the lowering of the surface of reclaimed peat is undoubtedly the greatest problem when attempting to sustain agricultural activities. It is caused by changes in conditions brought about by drainage. Waterlogged and anaerobic peat in the natural swamp becomes aerobic when drained. The aerobic conditions lead to biological oxidation or mineralization of the organic deposits. 99

Peat subsidence has several serious consequences. Drainage must be regularly adapted to new levels and conditions, otherwise inundation and flooding will recur. The rooting systems, particularly of perennial species become exposed (Plate 10), and top-heavy crops such as coconut palms and to a lesser degree oil palms start to lean over and are partly up-rooted (Plate 11). Roads and other structures become unstable, and as the drainage progressively breaks down, their surfaces become hummocky. Environmental effects will occur beyond the peatswamp confines; nutrient outflow will increase as the peat decomposes, and there will be an increase of CO 2 released into the atmosphere. Plate 9. High wood content of deep peat in coastal basin swamps in West Kalimantan, Indonesia. Vegetation is cassava (tapioca) Plate 10. Exposure of root system of palm caused by 5 years subsidence of moderately deep peat (less than 2m thick), Brazil The rate of subsidence depends on several independent and some interrelated factors of which oxidation of the organic materials is the most significant. The factors listed by Lucas (1982) can be grouped into the following categories: i. Processes causing the removal of organic materials: oxidation, burning, wind erosion and water erosion. ii. Processes causing consolidation of materials: compaction, shrinkage and dehydration. iii. Factors accelerating or influencing the processes mentioned under i. and ii. are: depth of drainage (height of water-table), character of the organic materials, the cropping system employed including irrigation, and the climate, particularly the temperature regime. iv. geological subsidence is an independent factor which would also play a role when artificial drainage was not provided. The subsidence of peat surfaces has been a problem ever since cultivators started to drain peat. There are long records of subsidence of reclaimed peats in both the Netherlands, where reclamation started between the 9th and 14th centuries (Schothorst 1977), and in the Fens of England where reclamation started in the 17th century (Darby 1956). Probably the best records on subsidence are available from the much more recent reclamation of the Everglades in Florida, USA, where subsidence has been monitored from the beginning in 1924 (Stephens 1956 and 1974; Stephens and Johnson 1951; Stephens and Speir 1969; Stephens et al. 1984). Reports on subsidence also come from Eastern Europe (Murashko 1969) and more recently from the tropical regions of South East Asia (Andriesse 1974; Driessen and Rochimah 1977; Driessen and Sudewo 1977) and Africa (Euroconsult 1984).

100

Plate 11. Palms leaning due to insufficient achorage after subsidence of deep peat, Sarawak, Malaysia. (Photo by Dept. of Agriculture, Sarawak). Subsidence rate Worldwide subsidence rates vary from less than 1 to more than 8 cm per year. Whereas some peats in the Netherlands have subsided by only 2 m in about 1 000 years, peat in the Everglades (Florida) has subsided by 1.8 m in only 54 years (1924-1978). The organic soils of the Sacramento-San Joaquin delta of California subsided by 1.8 to 2 m in less than 30 years. Records on peat subsidence in South East Asia (lowland oligotrophic coastal peats) indicate 50 cm to 1 m in the initial years after reclamation with a subsequent decrease to less than 6 cm per year. Table 21 gives the reported rates of subsidence for sites worldwide. It is clear that there is a vast range in the rate of subsidence dependent on peat composition, drainage depth and history of reclamation. Figure 19 illustrates how in the Netherlands subsidence rate was influenced by a change from gravity drainage to pumping once the peat surface fell below the mean sea level. Energy initially supplied by windmills, followed by the use of steam pumps made it possible to keep the swamps dry. The rate of peat subsidence in the Netherlands was small compared with rates experienced elsewhere mainly because the depth of drainage was maintained through the centuries at only 20-50 cm for mainly pasture use. However with deeper and improved drainage (water-table control throughout the year) the yearly subsidence rate of 1.7 mm was accelerated to 6 mm. Field experiments indicate that a 40 cm draw down of the level in ditches over a period of 20 years resulted in a total surface subsidence of 23 cm. In the first two years the subsidence proceeded very rapidly, constituting 44 per cent of the total for the 20 year period, subsequently the subsidence rate decreased to a constant 7 mm per year. This initial rapid subsidence upon provision of drainage is noted in most countries. Table 21 MEASURED RATES OF SUBSIDENCE OF ORGANIC SOILS FOR SPECIFIC SITES IN DIFFERENT AREAS (source Lucas 1982) Location of site

Annual subsidence rate (cm/year)

Cumulative subsidence (cm)

Average depth to watertable (cm)

California Delta (2 sites)

2.5-8.2

Louisiana (estimated)

1.0-5.0

Michigan

1.2-2.5

7.6-15

New York

2.5

150

Indiana

1.2-2.5

7.6-15

Florida Everglades

2.7

147

(2 sites)

2.7-4.2

19-29

Netherlands

0.7

70

(2 sites)

1.0-1.7

6-10

Ireland

1.8

Norway

2.5

152

65

England

0.5-5.0

325 (by 1932)

84

348 (by 1951)

103

Israel

10

USSR (Minsk bog)

2.1

152-244

Time period (year) 26

5 60 90 6 54 90 7 60 100 10-20 6 50 90

100

47

101

A knowledge of the expected subsidence rate is important in order to plan adaptations to the drainage system, estimate the lifetime of the organic soils, and assess the optimum land use. Subsidence rate is dependent on many factors, some of which can be changed and it is therefore necessary to discuss in detail the most important processes so that management plans can be developed which optimize the life expectancy of the peat deposits. Oxidation of peat Oxidation is generally taken to be the most important process causing loss of organic materials. Burning as a form of accelerated oxidation is mainly caused by man, and can be easily controlled or prevented. Water erosion and wind erosion are more difficult to control but are of little significance in tropical areas. Lucas (1982) reports from Canada that wind erosion has been one of the predominant causes of wastage, and losses of over 3 cm are noted during severe storms. The removal of peat by scouring in drainage channels, is locally important and coastal erosion occurs where peat is exposed on the shore (Andriesse 1974). In the tropics however none of these forms of peat removal compares with oxidation in lowering the surface level. Oxidation is a biochemical process intensively studied by Waksman and Stevens (1929) and Waksman and Purvis (1932). In laboratory studies they found different rates of decomposition in peats of different chemical composition and in peats containing different micro-flora and microorganisms. Samples of Florida low moorpeat were decomposed by 15 percent at 28°C in 18 months under optimum moisture conditions of 50-80 percent. Above and below this moisture range, decomposition rates rapidly diminish. Wet and dry cycles also appear to stimulate decomposition. Bacteria are commonly most numerous in drained low moor peats and less numerous in highly acid high moor peat. However, when the latter are limed, manured, and cultivated, microbial populations increase to about the same as low moor peat under similar drainage conditions, and decomposition rates increase likewise. Organisms responsible for decomposition are most active above 5°C. Soil microbial activity generally doubles for each 10 degree increase in temperature and soil temperature is therefore an important factor in determining subsidence rates, particularly for tropical areas where temperatures remain in the 25-30°C range. Depth of drainage is another important factor governing the rate of oxidation and it was studied by Schothorst (1977) in the Netherlands. Stephens and Stewart (1977) developed a mathematical model linking drainage depth and soil temperature that could be used to estimate subsidence of low moor peat in different climates. Figures 20 and 21 give the results of these studies; Figure 20 indicates the strong correlation between subsidence rate and average depth of the water-table, and Figure 21 depicts the relationship between expected annual subsidence with the two main variables soil temperature and depth of drainage. The latter graph is based on the mathematical model which was developed for organic soils with a mineral content of less than 15 percent and bulk density of approximately 0.22 g/cm3. Muck soils with higher mineral content and bulk density, will have subsidence rates between one-half and three-quarters of those shown on the graph. The model is only tentative and based on limited field and laboratory data, but, in the absence of empirical information, can be used to quantify subsidence caused by mineralization. Details of the model are given in Appendix 4.

102

Figure 19. Relation between evolution in water management and subsidence of peat surface in the Netherlands

103

Figure 20. Rate of subsidence compared with water-table depth for organic soils in Indiana, Florida Everglades and the Netherlands.

104

The two Netherlands lines show total subsidence and subsidence attributable to biological oxidation. The linear regression equations are: a. Florida, Y = 0.0643X - 0.259 b. Indiana, Y = 0.0344X - 0.429 c. Netherlands (total subsidence) Y = 0.0281X - 0.581 d. Netherlands (oxidation subsidence) Y = 0.0134X - 0.291 Where Y is the predicted subsidence in cm per year, and X is the average depth to water-table in cm Figure 21. Annual subsidence of organic soils at various water-table depths and soil temperatures

Consolidation and shrinkage Peatland subsides after drainage not only because of a loss in organic matter but also because of a loss in volume. Schothorst (1977) recognizes the following components in subsidence: i. shrinkage due to physical processes. The withdrawal of moisture from the surface layers by evapotranspiration may cause high moisture tensions in the root zone resulting in a decrease in volume of those layers (above the phreatic surface). ii. Oxidation through biochemical processes as explained above.

105

iii. Consolidation or compression due to a mechanical process. When the groundwater level is lowered, the buoyant force of water is lost in the upper layers. The deeper layers then have to bear an increased weight of 1 g per cm2 per cm of draw down of the groundwater-table. This causes compression by the soil layers below the phreatic surface. Consolidation is often divided into a primary phase and a secular phase. The former is largely a function of the rate of water escape from and through the peat mass. This can be very high in the initial phases of drainage because of the high permeability of raw peat. When permeability decreases as a result of consolidation the primary hydrodynamic phase becomes almost constant. Secular consolidation continues long after the primary phase has stopped to play its initial important role and may in the end account for half the total loss in volume. It was previously generally assumed in the Netherlands that the decreasing volume of peat above the water-table was controlled more by shrinkage and compression than by oxidation. This was the case because of the ubiquitous grass cover. Schothorst, however, found that 20 percent of the subsidence could be ascribed to irreversible shrinkage, 28 percent to compression (subject to elastic rebound and recovery) and 52 percent to oxidation. These results are in agreement with the general findings elsewhere that oxidation is the main cause for soil subsidence. It is important to note that compression and irreversible shrinkage will gradually decrease from an initial peak but that oxidation of organic materials will continue at a more or less constant rate until a new lowering of the water levels in ditches is necessary. This corroborates previously mentioned findings in tropical countries. Bouman and Driessen (1985) argue that the subsidence after drainage or reclamation is the sum of the effects of settling, shrinkage and mineralization. For this reason the mathematical model developed by Stephens and Stewart (1977) to estimate subsidence is only valid for the mineralization component, because it disregards the effects of shrinkage and compaction. They prefer to employ two models to predict overall subsidence for tropical areas by fusing the Stephens-Stewart model for the mineralization component and the Murashko equation (Murashko 1969, Appendix 4) for the consolidation component independent of climate. By adding the two, total subsidence under tropical conditions can then be approximated. Figures 22 and 23 give the total subsidence thus computed for an imaginary tropical peat over 20 years of drainage in relation to bulk and particle densities, and initial drainage depth respectively. Figure 24 indicates the computed partial subsidence rates for consolidation and mineralization. This shows the considerable influence of consolidation on subsidence in the initial years and the long term effects of continued mineralization.

7.3.2 Cultivation practices The crops grown and their cultivation requirements influence the rate of subsidence through various processes: Water management A comparison of subsidence rate under sugar cane, vegetables and pasture, using a given watertable depth, showed the annual rate of subsidence under sugar cane to be about 30 percent less than under pasture or vegetable crops (Snyder et al. 1978). Though in previous studies no conclusive evidence is available to show that the type of crop has a direct bearing on subsidence rate. Indirect effects are probably much more significant. Each crop has an optimum water-table level dependent on rooting habits, resistance to drought and wetness. Climatic conditions; rainfall, wind, evaporation and temperature are important parameters for calculating water requirements. Table 22 shows the minimum optimum depth of water-tables for a range of vegetable crops grown on various peats in the USA and England (Snyder et al. 1978). The range is large and varies from 30 to 90 cm depth. Sugar cane grown in the Everglades in Florida requires a water-table at 75-90 cm depth for optimum growth and quality but in experiments it was found that with a water-table at 38 cm depth the crop produced only 5 percent less sugar than the best yields obtained with a water-table at 75 cm depth. For one variety the best yields were obtained with a water-table at 38 cm depth. 106

In the Netherlands water-tables under grassland are usually maintained at between 30 and 50 cm depth which produces much smaller rates of subsidence than if crops requiring a much lower water-table are grown. A large subsidence rate will be experienced in tropical regions where tree crops are to be grown with extensive, deep rooting systems which demand deep drainage. Depth of drainage influences the rate of subsidence and therefore choice of crop or land use is indirectly related to the rate of subsidence. Land management A system of raised beds in conjunction with higher water-tables could be used to extend the life of peat deposits. Figure 25 demonstrates this and shows how two crops can be grown in adjacent rows each with an optimum depth of water-table. However, the system may be short lived if decomposition of the peat on the ridges is faster than in the drains. Although the system is successfully practised by Japanese farmers in Brazil (Plate 1) they do not grow a crop in the furrow. Use of fertilizers The high acidity and low levels of plant nutrients in peat demands the use of lime and fertilizer for crop growth. The change from oligotrophic to more eutrophic conditions as a result of fertilization changes the microbial activity and hence the rate of mineralization (Chapter 4; section 4.3). The use of fertilizers therefore tends to accelerate decomposition. However, McGreevy and Farrell (1984) found in incubation experiments few lasting effects in ombrotrophic peats after an initial stimulation. In reed-swamp peat, decomposition was even reduced by liming to pH 6.5. General statements on the effect of liming are therefore dangerous as there are other factors to be considered. The dilemma of using fertilizers or not can be illustrated by the following example. Schothorst (1977) records studies in the Netherlands on the improvement of gross yield of grass through deeper drainage. The improvement could be attributed to the availability of more nitrogen as a result of the decomposition of peat to a greater depth. The deficiency in nitrogen occurring in grassland with shallow drains can also be corrected by more costly N-fertilization. The choice between either deeper drainage with its risk of accelerated subsidence or the use of costly Nfertilizer is often difficult. Cropping system The cropping system influences the amount of compaction of the soil surface. The regular harvesting of intensively grown vegetables, particularly if heavy machinery is used, makes heavy demands on surface structure and consistency. Where annual crops are grown there are often short fallow periods. The surface temperature in these exposed peats can reach 70°C in the tropics as peat is a very poor conductor of heat. As well as encouraging the formation of desiccated hydrophobic granules (“coffee grounds”) or dust, this also increases the rate of oxidation. Bare peat surfaces, low humidity and high temperatures can lead to spontaneous peat fires. A permanent groundcover would prevent this.

107

Fig. 22. Subsidence (S t ) of tropical peat in relation to bulk and particle densities (source Bouman and Driessen 1985)

Note: r = dry mass of unit volume of undisturbed soil r s = solid matter (particle) density

108

Fig. 23. Subsidence (S t ) of tropical peat in relation to initial drainage depth (source Bouman and Driessen 1985)

109

Table 22 MINIMUM DEPTH TO WATER-TABLE (CM) FOR MAXIMUM YIELDS AND QUALITY OF VEGETABLE CROPS GROWN ON ORGANIC SOILS (source Snyder et al. 1978)

Florida Everglades 1

Crop

Indiana 2

England 3

Minn. 4

Beans, snap

45-60

-

-

45

Beets (red)

-

70

-

-

Cabbage

45-60

65

-

60

Carrots

-

65

-

60

Cauliflower

60

-

-

30

Celery

45

65

45-55

45

Corn, sweet

60-70

75

-

60

Kale

-

-

60 +

-

Lettuce

75-90

-

-

75

Onions

45-60

75

-

90

Peas

45-60

-

-

-

Potatoes

45-60

65

40-50

60

Spinach

-

65

-

-

Tomatoes

45-60

-

-

60

Escarole

60-75 5

-

Endive

60-75 5

-

5

Radishes

35-40

Parsley

35-40 5

45 -

1

Eight water-table treatments: 75 cm with overhead spray, 30, 53, 75, 100, 120 cm, fluctuating, 120 cm with overhead spray (the experiment was replicated). 2

Three water-table levels, two replications, 40, 70 95 cm.

3

Water-tables ranged from 25 to 95 cm (unreplicated).

4

Five water-table depth treatments: 30, 60, 90, 120, 150 cm (unreplicated).

5

No data have been found on these crops, and depths given are estimates under average Everglade conditions.

110

Figure 24. Partial subsidence rates (consolidation and mineralization) for tropical peat (source Bouman and Driessen 1985)

Note: S m = subsidence due to mineralization

111

7.4 Water-table Management The success of agriculture on peat soils depends on the choice of land use. This choice dictates the required drainage depth though in some localities the water levels in peatswamps are governed by the needs of peripheral areas. Figure 25. The influence of raised beds which allow a higher water-table and hence reduce the oxidation of organic soils (source Snyder et al. 1978) The cropping systems in common use today inevitably cause some subsidence. There is a wealth of historical evidence that once drainage has started subsidence commences and unless the swamps are inundated again the peat will eventually disappear. Radio-carbon studies have indicated that 30 cm of peat which took 400 years to develop can easily be destroyed in less than 10 years because of injudicious drainage. The rate of subsidence can, however, be regulated and slowed down by proper water control and good land management. The careful choice of crop is the best way by which the rate of subsidence can be minimized. There should be continued collaboration between drainage engineers and agricultural scientists to look for optimum ways of controlling the subsidence of peat by appropriate water, land and crop management. The search for new crops or new varieties to be grown profitably in more waterlogged conditions and a continuation of the work into the water-table requirement of crops should be major parts of the research programmes aimed at improving the management of reclaimed peatswamps. In the tropics there is little locally gathered data on the water management requirements in relation to widely grown crops. Traditionally the emphasis has been on the short term problems of fertilizer requirements rather than on water-control measures, which are more important in the long run. It is difficult to set up satisfactory experiments to look into the optimum depths of the groundwatertable for specific crops. The following serves as an example: expensive and comprehensive watertable studies have been carried out in the Everglades in Florida since 1958 (Harrison et al. 1963), but they have proved unsatisfactory. It is difficult, even when using intricate designs, to maintain a range of pre-determined water-tables in plots arranged in a 3 x 3 Latin square on a 24 acre block. Subsequent studies have shown that the drainage of the peats overlying limestone is considerably affected by sub-surface flows through the peat-rock interface (Casselman and Green 1972). Mole drainage appears to have little effect on these flows along the interface. Piling the plots or building concrete walls down to the more or less impermeable subsoil have to be established, but even then hydraulic pressure from high water-tables in neighbouring parcels influence the plots with lower water-tables. In the absence of reliable tropical field studies and taking into consideration the difficulties encountered elsewhere, the alternative is to use lysimeters. These concrete tanks, if built of about 150 x 300 x 150 cm size, can each be used for 3 separate plots of 150 x 100 cm size for crop studies. When filled with organic soil water-tables are maintained by an exterior water levelling container connected by a 1 cm internal diameter plastic pipe. Water-levels in the levelling container are maintained by a valve with holes in the container immediately above the desired water level for overflow. Holes should be drilled into the concrete tanks at the soil surface level to allow surface drainage (Pate and Snyder 1979).

112

8. AGRICULTURAL MANAGEMENT 8.1 Introduction 8.2 Crop Choice 8.3 Water Management at Farm Level 8.4 Tillage and Cultivation Methods 8.5 Correcting Acidity by Liming 8.6 Fertilizer Use 8.7 Crop Protection

8.1 Introduction Before cropping commences the farmer has to make important decisions which profoundly affect the subsequent operational management. First he has to choose the crop; the operational requirements generally follow from this. Such operational requirements at farm level include: i. Water management in relation to crop moisture requirements. ii. Tillage and land preparation. iii. Liming or acidity control. iv. Fertilizer use. v. Crop protection. This chapter covers many topics because of the intrinsic variability in organic soils, climatic conditions, crop choice and land utilization policies. Socio-economic factors such as quality of farm management, capital investment, land tenure and the organization of water management in drainage, contribute to the complexity of the issues concerned. It is only possible to highlight information which is generally applicable and useful for practical field operations, and details relating to conditions that are found only locally in tropical peat soils are left out. There is therefore no comprehensive discussion on specific crop requirements. Many standard management practices used on mineral soils are also applicable to organic soils so they are not discussed in detail. Emphasis is placed on all aspects of agricultural management specific to conditions prevailing in organic soils.

8.2 Crop Choice 8.2.1 Choice of crop under natural drainage conditions 8.2.2 Choice of crops under improved drainage with water-table at less than 40 cm depth 8.2.3 Choice of crops assuming deep drainage

Crop choice is dependent upon many factors of which suitability of soil is but one. For most farmers profitability is the overruling factor, but in the case of reclaimed peatswamps there are a number of factors which influence or limit the freedom of choice and which are beyond the control of the farmer. In the case of large peatswamps reclaimed by a Government, or government agency, the potential land use has been decided early in the scheme. Large-scale reclamation schemes need careful overall planning and the control of drainage cannot be left to the individual farmer. However, within the limits set by the controlling body it is possible to have some influence on water control at the farm level by such means as stop boards, but generally the margins are small. It is, therefore, the 113

depth to which the groundwater is maintained in the reclaimed area that largely controls and limits the choice of crop. In cases where an individual farmer endeavours to reclaim small stretches of swamp, he has more room for taking his own decisions. However, if his land is part of a much larger swamp he has the moral, if not legal, obligation not to disrupt farming activities on fields lying downstream. Such conditions are frequently found in long narrow interior valleys especially when under private ownership. In such cases it would be sensible to look for more participants in a concerted reclamation effort which would ensure a balanced development of the complete swamp. It would be unwise to develop one part of the same swamp for deep rooting crops demanding a drainage depth of say 90 cm, if on a neighbouring farm attempts are made to keep the water level at 40 cm for pasture development. Crop choice is also influenced by independent climatic factors and socioeconomic considerations such as marketability, which are liable to fluctuations. Peat soils are remarkably versatile in their suitability for crop growth. They have few inherent qualities which limit growth, although they require intensive and often costly improvement to natural conditions to make cropping profitable. Profitability is again largely dictated by the local economy. Peat is a good stoneless rooting medium, it has large moisture retention capacity and hence transplanted crops establish themselves much faster than on mineral soils. Cultivations are easier than on mineral soil, even under exceptionally wet conditions. There are, however, also serious limitations to cropping: i. Waterlogged conditions, requiring drainage. ii. Very low chemical fertility, requiring large applications of fertilizers. iii. High acidity, requiring liming. iv. Low trafficability, preventing intensive mechanized farming. Most of these limitations can be remedied but sometimes only with capital investment. In some localities improvements are economic but in others the necessary improvements are prohibitively costly. Most countries have already developed or should develop their own peat suitability ratings, adapted to local conditions, taking into account the limitations mentioned and based on local economic considerations (Chapter 6). A very general guideline, based on experience in South East Asia, and which can be adopted elsewhere with similar conditions, is to limit farming to peats which are less than 2 m thick. Greater thicknesses, particularly those with a low level of management, usually have insurmountable problems. This depth requirement can be adjusted to fit local situations and where the input levels of water control, fertilization and crop protection are high deeper peats can be contemplated. Although factors mentioned play an important role in crop choice, they are specific to a locality and should be studied and evaluated for each site. Despite this complexity of factors, it is possible to discuss crop selection by looking at the various land use options possible under three systems of water-table management; natural conditions, somewhat improved drainage but with shallow water-tables (less than 40 cm depth), and with deep drainage (water-tables generally greater than 60 cm depth).

114

8.2.1 Choice of crop under natural drainage conditions There is an increasing interest in developing an adapted form of agriculture which leaves the peatswamps largely in their natural state. Crop selection is directed to finding suitable swampadapted plant species of economic value. This type of farming would to a large extent solve the problem of subsidence (Shih et al. 1982). The main crops suited to such conditions are: Sago Sago (Metroxylon sagus, a smooth variety, and Metroxylon rumphii, the thorny variety) is grown in the natural peatswamps of Sarawak and elsewhere in the Malay-Indonesian archipelago under wild and semi-wild conditions. There is evidence that the crop could give reasonable returns, and organized production on a large scale could be lucrative. The produced starch can be used, as a food, by industry and as a raw material for the production of methanol. As a result of better vegetative dry matter production per day and a longer period of closed canopy, the sago palm is superior in potential to cassava and rice (Ahmed and Sim 1976). Raffia The raffia palm (Raphia spp.) and papyrus (Cyperus papyrus), indigenous species in African peatswamps, can be grown commercially provided that local markets are available and the range of its industrial use can be widened. Rice Rice is probably the most swamp-adapted foodcrop. Wild rice (Zizania aquatica and Zizania palustris), of which a number of varieties are commercially grown in North America, even as far south as Florida, appears to offer good possibilities under the right climatic conditions in natural peatswamps. This rice, famed as a gourmet accompaniment for wild duck and game, also has a ready market as a dietary food because it is a good source of thiamine, riboflavin and nicotinic acid (Morton et al. 1980). Wild rice needs some regulation of water-tables for optimum growing conditions although it thrives in waterlogged conditions. Aeration of the water is however essential and regular flooding with oxygenated water is beneficial. The optimum pH is between 7.5 and 8.0 which excludes most tropical peats unless they occur near a brackish water source in the fringe areas between mangroves and freshwater swamp forest. For a number of reasons the domesticated rice (Oryza sativa) requires very good water-table control and is therefore not suitable for peatswamps. It is discussed under the section dealing with conditions of shallow drainage. Wetland taro Another starch foodcrop, wetland taro (Colocasia esculenta, var. aquatilis) has many wetland cultivars. It is grown in and around the Pacific as well as in India and Africa in similar locations to wetland rice. Larger plantings require field levelling, puddling by ploughing, disking, harrowing and grading. It is also necessary to have constant water circulation to avoid footrot. Since many tropical peatswamps, particularly in their centres, have deoxygenized water, favourable conditions only occur near their edges where peat merges into mineral deposits. Nutritionally taro is a better choice of crop than rice, as the amino acid content is as high as in potatoes and the crop should be grown more widely in wetlands.

115

Miscellaneous crops Water celery (Oenanthe javanica), water spinach (Ipomoea aquatica), and the Chinese water chestnut (Eleocharis tuberosus) when grown commercially, require some expertise and the vegetable crops are limited by location and marketability. Water chestnuts, like rice, are grown in fields covered with 5-10 cm depth of water. Tubers can be eaten in salads and soups, the juice has antibiotic uses and the sedge can be made into matting although it is not very durable. Most crops, including those mentioned above, require a plentiful supply of oxygen in the water, and relatively eutrophic conditions for good growth. The true tropical lowland peats of an oligotrophic nature are often not suitable and the best conditions are found in shallow peat and in those with an appreciable amount of mineral matter.

8.2.2 Choice of crops under improved drainage with water-table at less than 40 cm depth Pasture By far the greatest area of reclaimed peatswamps in temperate regions is used for pasture and these only require the water-table to be lowered to about 40 cm depth. In the Netherlands a watertable depth of about 40 cm has been maintained for centuries which has minimized the rate of subsidence. The largest area of peat in the Florida Everglades is used for pasture, particularly St Augustinegrass (Stenotaphrum secundatum). Apart from requiring shallow drainage, grassland use does not necessitate intensive mechanization which is characteristic of large scale vegetable growing. Pastures can be used for direct grazing but the high water-tables lead to low surface bearing strength and pastures are unsuited to frequent and heavy traffic. In the tropics pastures on deep oligotrophic peats require high levels of fertilizer application and therefore the nature of the peat should be carefully examined and likely improvements considered in the light of local economic perspectives, before large scale pasture development is contemplated. Conditions will most likely only be favourable in a few selected localities. The growing of fodder crops such as Napier grass is probably locally more attractive than grazing. The careful selection of grass species also counteracts the effects of poaching and in Florida, St Augustinegrass is used effectively in this capacity. Rice Rice (Oryza sativa) has received much attention as being the crop most adapted to swamp conditions. The cultivation of rice on true tropical peats of oligotrophic nature has a number of drawbacks of which the most important are sterility, causing empty panicles, and the crop’s dependence on good water control. Although the latter is only essential for obtaining high yields, the former is often the cause of complete failure. The cause of sterility is not exactly known although copper deficiency probably plays a major role and dressings of copper can alleviate the problem. Driessen and Suhardjo (1976) suggest that copper deficiency retards the inactivation of the toxic phenols and causes male sterility. However, Japanese work by the Central Agricultural Experimental Station and reported upon by Miyake (1982) indicates that the disorder is caused by harmful substances produced by delayed and incomplete decomposition of organic materials. He postulates that disorder can be cured by drainage improvement. Both findings may be complementary, in that it is possible that retarded decomposition causes the formation of copperfixing organic compounds, and thus, by stimulating the decomposition rate by drainage, the same effect would be obtained as a copper dressing. In both cases good management is required.

116

Rice fields in peatswamps where water levels are not adequately controlled may be frequently inundated by undrained rainwater and floodwaters become too high; such periods may be followed by periods of water shortage causing drought stresses in the crop. Rice growing on peat, though having some potential, therefore requires good water management involving both drainage and irrigation, and consequently level fields. The generally low or very low fertility of the majority of tropical peats, added to the problems of water control and sterility makes rice growing unprofitable in most countries, unless good management can be given and well-tried adapted cultivars are used. Vegetables In many countries organic soils are highly regarded for vegetable growing because of their excellent physical properties as a medium for plant growth. The choice of which vegetables to grow is dictated by many factors some of which (climate and locality) cannot be influenced by management. The minimum depth of water-table required for maximum yield and quality also limits the crop choice. Depth of water-table is often standard over large areas. Table 24 and Appendix 3 give indications of vegetable crops which can be grown with shallow drainage (water-table at less than 60 cm depth). The ultimate choice however often depends on the demand and price. Some tropical and sub-tropical crops such as chili, soya bean and tobacco should also be mentioned here because their method of cultivation is comparable with that of vegetables. They can also be grown successfully on peat soils with shallow drainage. Where peatswamps are in areas remote from large population centres, vegetable growing is not a commercial proposition particularly for rapidly perishable leafy vegetables. Non-perishable crops which can be stored and/or dried can often be grown profitably some distance from a market. Horticultural crops In temperate regions, particularly in the Netherlands, horticultural cropping is favoured on peat soils. Here the expansion of the horticultural industry was largely based on the excellent qualities of the local peat soils. Sandy mineral soil, from nearby riverbanks or dunes, is often mixed with the surface soil further improving the inherently good physical characteristics of the peat (Hidding 1982). In Japan mineral soil dressing is also practised for wet rice cultivation (Miyake 1982). Transplanting horticultural crops is easy and successful in peat because of the good root balls formed by the plants. Horticulture can be profitable in the tropics on oligotrophic peats, drained to 50 cm depth, assuming a good local market and an adequate level of management.

117

Table 24 MINIMUM WATER-TABLE DEPTH FOR MAXIMUM YIELD AND QUALITY OF CROPS GROWN ON ORGANIC SOILS (source Lucas 1982) Crop

Florida

Indiana (Depth in cm)

Minnesota

Beans

45-60

-

45

Beets (red)

-

71

-

Cabbage

45-60

66

60

Carrots

-

66

-

Celery

45

60

45

Corn

45-75

75

60

Lettuce

75-90

-

75

Mint

-

75

-

Onions

45-60

75

90

Potatoes

45-60

66

60

Parsley

35-40

-

-

Radish

35-40

-

45

Pasture-sod

30-50

45

-

Sugar cane

60-75

-

-

8.2.3 Choice of crops assuming deep drainage Deep drainage is defined as greater than 60 cm depth but some crops require a depth greater than 90 cm (Table 24 and Appendix 3). Perennial crops The growing of perennial crops, particularly plantation crops on tropical peats, has been under study in Malaysia for some time (Kanapathy 1978; Tie and Kueh 1979). One of the most difficult problems to counteract is the poor root anchorage provided by the soft peat, especially for crops such as coconut palm (Cocos nucifera), oil palm (Elaeis guineensis) and rubber (Hevea brasiliensis) (Plates 10 and 11) which become top-heavy when mature. Peat subsidence, a consequence of intensive drainage, uproots the shallow-rooting trees causing them to lean progressively and eventually topple. This problem can be partly alleviated by using dwarf varieties. Attempts are currently underway to breed a dwarf oil palm for this purpose (Dolmat et al. 1982). It is only where the peat is shallow (less than 2 m thick) and contains an appreciable amount of mineral matter that such crops are feasible. Thus deep oligotrophic peats are unsuited because of low fertility and poor anchorage though small subsistence farmers may have marginal success when world prices are favourable. Fruit trees and horticulture The yield potential of some promising perennials and previously mentioned annuals grown on deep oligotrophic peat in South East Asia is shown in Table 25. This potential is only realized under very good management and with high inputs of fertilizers. The economic feasibility is therefore low.

118

Large-scale banana (Musa spp.) growing in the Ivory Coast with drainage at 80-100 cm depth on acid oligotrophic coastal peat, comparable with the lowland peats of South East Asia, indicate that yields in the first years are in the range of 25-30 t/ha but could eventually reach a level of 35-40 t/ha. However, initial investments are higher than on other soils and banana cultivation on peats is difficult and demands good management (Lassoudière 1976). In general this is true for most horticultural crops grown on tropical peats. Sarawak sources (Tie and Kueh 1979) indicate a high potential for mulberry (Morus alba) which, however, would require the initiation of a local silk industry. In general many fruit crops, though performing well, are plagued by bird damage, insect pests, nematode and disease problems. Therefore, these crops also need a high level of crop protection for success. Food crops Root crops require well drained conditions to prevent tuber rot and large inputs of fertilizer. Under subsistence farming peat burning is traditionally practised to ensure adequate potassium levels but because this exacerbates wastage it should not be encouraged. Cassava (Manihot esculenta) or tapioca, yielding up to 50 t/ha with good management, is an important food crop on well drained deep oligotrophic peat in the tropics. Miscellaneous field crops A number of perennial or semi-perennial crops are difficult to place in the categories mentioned above. Of these pineapple (Ananas comosus) has a very good potential, because it both flourishes in the acid conditions prevalent in peat soils, and it is relatively low growing and not susceptible to being uprooted at maturity. The Malaysian pineapple industry is based predominantly on deep oligotrophic peats. Sugar cane (Saccharum officinarum) is grown successfully on the Everglade peats in Florida and on deep coastal peats in southern states of Brazil, the latter for methanol production. Good management and assured markets are prerequisites to the economic feasibility of sugar cane growing. Summary While drained peats form an excellent growing medium for many crops it is only through the development and employment of specific technology for each crop that the inherent potential can be realized. In many countries the capital investment necessary for improvement is too high and management levels too low to justify reclamation.

119

Table 25 YIELD OF SOME PROMISING CROPS ON PEAT IN SARAWAK AND WEST SELANGOR, MALAYSIA (source Tie and Kueh 1979) Common name Botanical name Sarawak West Selangor Yield (t/ha) Pineapple

Ananas comosus

40.0 fresh fruit

40.0 fresh fruit

Tapioca (cassava)

Manihot esculenta

50.0 fresh fruit

49.0 fresh tuber

Tobacco

Nicotiana tabacum

0.7 dry leaf

1.0 dry leaf

Groundnut

Arachis hypogaea

1.0 dry seed

3.5 fresh nuts

Soya bean

Glycine max

1.5 dry seed

-

Cowpea

Vigna unguiculata

2.1 dry seed

-

Bambara groundnut

Vigna subterranea

1.5 dry seed

-

Sorghum

Sorghum bicolor

1.5 dry seed

2.5 dry seed

Sweet potato

Ipomoea batatas

14.0 fresh tuber

24.0 fresh tuber

Castor oil

Ricinus communis

2.5 dry seed

-

Ginger

Zingiber officinale

15.0 fresh rhizome

15.0 fresh rhizome

Okra

Hibiscus esculentus

6.0 fruit fruit

15.0 fresh fruit

Oil palm

Elaeis guineensis

19.0 fresh fruit bunch

-

Sago

Metroxylon sagus

6.0 dry starch

-

Coffee

Coffea liberica

1.7 fresh berries

-

Annatto

Bixa orellana

2.0 dry seed

-

Mulberry

Moms alba

13.0 fresh leaf

7.5 dry leaf

8.3 Water Management at Farm Level 8.3.1 Systems of open drains 8.3.2 Subsurface drains 8.3.3 Irrigation The provision and maintenance of adequate water control systems in peatswamp reclamation require two distinct types of management; one at the individual farm level and another for the peatswamp as a whole. The latter is responsible for major constructions such as dams, dike’s, levees, canals and main ditches, whereas the farmers are usually responsible for the construction and maintenance of farm ditches and/or field drains. The aim of water control systems is both to provide adequate drainage for optimum crop yield and to maintain the water-table at an optimum depth to prolong the life of the organic soil. Initially stagnant surplus water must be drained away, thereafter the water-table should be lowered to and maintained at a depth where crop growth becomes possible. However, the peat should never be allowed to dry out to such an extent that irreversible drying will set in. In tropical areas, where the climate is characterized by a pronounced dry season, drainage facilities should be supplemented by irrigation, so that in periods of drought water levels can be maintained at the desired height by infiltration. An adequate source of irrigation water must therefore be available.

120

The reclamation of small swamps within a farm or group of farms is usually carried out by the farmer or farmers concerned. Large swamps are usually reclaimed by public bodies. This Bulletin describes the reclamation management required at farm level and does not describe at length the engineering requirements for large reclamation schemes. The problems of co-ordinating and integrating drainage requirements of many individual farms must not be underestimated. Further, with regard to swamp drainage on an individual basis, the effects on groundwater levels and risk of flooding on neighbouring farms, should be borne in mind.

8.3.1 Systems of open drains The size of open drains is related to the amount of rainfall which must be removed and the height of the groundwater-table to be maintained. Climate, in particular rainfall, and the lateral and vertical hydraulic conductivity of the peat are the most important criteria in drainage design. Generally, the nearer the water-table is held to the optimum depth for the individual crop, the better the yield. Tie and Kueh (1979) quote recommendations for drains at 90-150 cm depth at 100-200 m intervals together with field drains at 50-80 cm depth, placed at right angles to the main drains at 15-30 m spacing. Tay (1969) describes a similar system used by the Drainage and Irrigation Department of Malaysia for peat less than 1.5 m thick (Fig. 26). For thicker peats a system of ring and feeder drains is recommended (Fig. 27). Such systems do not allow irrigation in periods of drought. In Indonesia a system is used which allows both drainage and irrigation by utilizing the tidal differences in water levels of the main canals (Fig. 28). The system works as follows: during high tides water enters the canal system backing up and raising the fresh water in the system so that parts of the land can be irrigated by submersion. During low tides the water levels in the system fall, including the main tertiary and field drains. Owing to the relatively long length of the system, not all of the drainage water is discharged to the river. To catch this, water tanks are constructed at strategic points to be filled during the next tide. This water is conveyed to the system when the next fall in water level reaches its minimum at the bottom of the tertiary drains. In practice, serious siltation occurs in the tanks, but where the silt load in rivers is low the system is feasible. However, it is only through the provision of structures such as tidal gates, sluices and pumps that good use can be made of a combined irrigation and drainage system in coastal lowlands. As a means of water control at field level stop-boards are widely used in tertiary drains. The height of the water-table can then be easily adjusted within limits to suit the need of the individual crop and growing period.

121

Figure 26. Drainage system for relatively shallow (<1.5 m) peat (source Tay 1969)

The land is divided by main drains (1.5 m deep, 1.2 m wide) into rectangular blocks of 200 x 600 m. Within each block, secondary (1.2 m deep, 0.9 m wide) and field (0.9 m deep, 0.6 m wide) drains are constructed.

8.3.2 Subsurface drains In Florida an increasing use is made of corrugated plastic tubing to replace field drains. This is easier to install than clay tiles, although it may be more expensive. Drain pipes should be 10-30 m apart depending on the permeability of the peat, the rainfall and the cropping system. Observations of water levels at about 2 m intervals between the pipes give information on the efficiency of the subsurface drains. These dipwells can be made out of 1.5 m long by 10 cm diameter downspouts with a stabilizing collar placed 30 cm from the top (Lucas 1982). The disadvantages of tile drainage are their vulnerability to silting up with either organic or iron oxide compounds, the cost and their possible disruption by tree roots. Mole drainage is an alternative method but its effectiveness depends on the nature of the peat. In finely-divided materials mole channels soon close up and become ineffective. An advantage of underdrainage is that the tiles can be used to irrigate in times of drought by reversing the direction of water flow in the main open ditches or canals, but its success depends on soil permeability and the smoothness of the field surfaces.

122

Figure 27. Drainage system for deep peat (> 1.5 m) (source Tay 1969)

A large circular drain is constructed round the land with feeder drains proceeding inwards to the centre.

123

Figure 28. Combined drainage and irrigation system using tidal differences (source ESCAP 1978)

8.3.3 Irrigation The amount of water available to plants at critical periods in their growth is crucial to obtaining good yields. For optimum growing conditions it is therefore necessary to monitor moisture conditions in the peat soil. Neither excess nor insufficient water should be present in the rooting zone. This is particularly so for high-quality vegetable crops that demand large investment of capital and labour for optimum production. The peat surface should never be allowed to dry out and frequent watering may be necessary in dry periods. Where this cannot be maintained manually, overhead sprinkler devices, drip irrigation or surface flooding is necessary. Subsurface irrigation, as explained above, is generally favoured because of low costs and there are no problems with the quality of water sources (low alkalinity or salinity hazards). Overhead irrigation is necessary wherever fields are not level. A great many systems, catering for many varied local conditions, are in use, each with merits and handicaps. The factors to be considered when choosing equipment are labour costs, ease of handling, damage to crops, water distribution patterns and field puddling. Water used for irrigation should preferably have a conductivity of less than or 750 mmho/cm (650 ppm of salt)

124

8.4 Tillage and Cultivation Methods Good tillage on peat avoids breaking down the peat particles to dust. Too much tillage leads to wind erosion of the fine particles and rapid dessication in dry spells. Organic soils are inherently loose structured and require little power to cultivate, although variations occur because of the relative proportions of mineral particles and wood. Too many wood fragments prevents good ploughing and large fragments have often to be removed by hand. Deep ploughing is often carried out in temperate countries, particularly in the Netherlands, to mix the peat with underlying mineral soil, frequently sand. This mixing of sand and peat creates an excellent medium for plant growth and also increases the bearing capacity. If the mineral subsoil is clayey it is more difficult to obtain a good mixture, but clay admixtures have greater adsorption power for fertilizers. In Japan the system of topsoil dressing of deep peat soils with mineral materials is well established for padi cultivation. The physical characteristics of peat often require adjustments to conventional ploughing equipment. Peat can be too loose for ploughing so that it is pushed by the plough rather than inverted. In the tropics, high wood content and hummocky peat surfaces are often the main obstacles in preparing a good seedbed. Mechanization is difficult because of the lack of levelling equipment and manual tillage is therefore often practiced. Perennial crops or those requiring root stock propagation are therefore favoured by the tropical subsistence farmer rather than crops produced from seed. In temperate regions, farming on peat soils is highly mechanized, while in developing countries conditions are generally unsuited to mechanized farming. Large-scale mechanized farming is often not cost-effective on the majority of tropical peats and much of the mechanized equipment is not discussed here. It is common practice to plant on ridges or raised beds, particularly in the case of vegetables. Damage from waterlogging after heavy rains coupled with inefficient drainage can be avoided in this way. The danger of desiccation is however enhanced and in certain climates the soil surface has to be irrigated frequently (Plate 1). To overcome the problem of uprooting with top-heavy perennial tree crops or palms, the crops in Malaysia are planted by the double hole, or hole-in-hole method. A hole of 1 m2 and 30 cm deep is dug in the freshly reclaimed and drained peat. Within this large hole an oil palm seedling is planted in a normal size planting hole of 45 cm diameter and 35 cm deep. As the surface of the peat subsides because of shrinkage and compaction, the base of the young palm becomes level with the peat surface. By this method the impact of the first rapid and intensive subsidence of about 40 cm in two years can be cushioned. Subsequent subsidence is rather slow and of less significance. There has been very little research on cultivation techniques on tropical peats, probably because most peats appear to be economically unsuited for large-scale cultivation. The exception is for pineapples but apart from this there has been little stimulation to research.

125

8.5 Correcting Acidity by Liming 8.5.1 Lime requirements 8.5.2 Materials used The acid or very acid condition of many tropical peat soils does not suit most commercial crops. Liming is therefore a prerequisite for most agricultural enterprises. The relationship between acidity and base exchange characteristics in peats has been described in Section 4.2. Many crops require a pH of over 4.5 for optimum growth. A few, such as pineapple and sago, like the low pH of peat soils. The amount of lime required depends on the natural acidity of the peat and the specific requirement of the crop. It is impossible to indicate here specific lime requirements for the great variety of crops which can be grown on peat soils. However, some general points can be made.

8.5.1 Lime requirements Many soil testing laboratories use buffer solutions to help estimate lime requirements. Some of these solutions are not suitable for organic soils as they were developed for mineral soil with different exchange characteristics. Mehlich (1942) developed a suitable test using a pH 6.6 buffer containing triethanolamine, acetic acid, ammonium chloride and sodium glycerophosphate. Liming was recommended if soil in the buffer was less than pH 5.5 (Lucas 1982). It should be added that lime recommendation also depends on the crop grown. Natural pH values and optimum CaCO 3 content of peat for agriculture is confusing because the type of peat is rarely given when results are discussed. The amount of lime required per unit change of pH varies for different soils depending on exchange characteristics. The proportion of mineral matter and the amount of exchangeable Al are both important. Generally a pH rise of 0.1 can be achieved by thoroughly mixing 0.7 t/ha of limestone to a depth of 15 cm. Lassoudière (1976) reports that an application of 5 t/ha of lime raised the pH one unit in coastal peat of the Ivory Coast. Similarly in Sarawak an application of 5 t/ha raised the pH from 5.7 to 6.6. However, the depth to which the pH increase is effective is also important as indicated in Table 26, based on liming studies with blanket bogs in Ireland which are chemically similar to oligotrophic peats in the tropics. Table 26 EFFECT OF LIME AND FERTILIZER ON THE NUTRIENT STATUS OF THE SOIL (source O’Toole 1968) 1

Ca, P and K as ppm in wet peat

O’Toole (1968) showed that generally very large amounts of limestone are required to substantially increase the pH throughout the rooting depth. Tropical oligotrophic peats where the pH is between 3.5 and 4.0 require at least enough lime to raise the pH one unit for most field crops including vegetables. Corn and alfalfa need a pH of 4.6-5.0 and onions require a pH of at least 4.3. In Sarawak, Tie and Kueh (1979) indicate that maize, groundnut and tapioca (cassava), grown on peat limed to a pH of 4.6, yielded significantly better than crops grown on unlimed peat of pH 3.2.

126

Several factors modify the critical pH for good plant growth, including the crop sensitivity to active calcium content. In general, organic soils with low Fe and Al contents can have an optimum pH value as low as 4.5 for certain crops, whereas peat soils containing appreciable amounts of Fe and Al have an optimum pH value approaching 5.0 for the same crops. Liming to neutral state is expensive and unnecessary. It may affect the availability of trace elements and over-liming may influence denitrification, producing toxic levels of nitrate-nitrogen. O’Toole (1968) showed that where an adequate supply of nitrogen fertilizer is applied to pasture the pH can be maintained at lower levels than where no applications are given. The influence of liming on the dry matter output of a mixed grass-clover sward is shown in Figure 29. Comparison with data in Table 26 illustrates that the best results are obtained when 2.5 t/ha of calcium carbonate is applied which raises the pH to 4.8. Figure 29. Effect of calcium carbonate on dry matter output from a surface seeded grassclover sward (source O’Toole 1968) Liming an acid peat to a pH of over 5.2 appreciably depresses the phosphate recovery and large quantities of calcium, and in the case of dolomite application also magnesium, may interfere with the absorption of potassium by the plants. It is sometimes alleged that liming increases the rate of decomposition of peat but the results of research give variable results and are inconclusive. The type of peat probably plays an important role (section 7.3; subsidence). Tie and Kueh (1979) give general recommendations for liming deep oligotrophic lowland peats of South East Asia based on the work of several researchers in Malaysia. They indicate that pineapple and sago need no liming, as does tapioca (cassava) if the initial pH is above 4.0 but at pH 3.5 and below, 5.0-7.5 t/ha of ground dolomite is recommended. Most other crops, like sweet potato, maize, groundnut, soya bean, sorghum, coffee and napier grass require between 5 and 10 t/ha of ground dolomite. This order of application is very costly, particularly as to maintain the pH at the required level necessitates an annual application of about 1.25 t/ha. In many cases, therefore, liming is a prerequisite for profitable farming. The optimum pH values and rates of application to achieve this vary considerably from crop to crop and between different types of peat. When assessing adequate levels of liming local experimentation is important as optimum pH levels are partly dependent on local economic factors.

8.5.2 Materials used There are two main materials used for liming; limestone, which is relatively pure CaCO 3 with less than 1 percent MgO, and dolomite, a CaCO 3 and MgCO 3 mixture containing over 15 percent MgO. The pure materials act faster to raise the pH than the dolomitic ones though the latter supply magnesium which is deficient in many peats. Proximity to source and transport costs of these bulky materials often determine the local choice of materials. Occasionally marl, which usually has admixtures of mineral material, and coral lime are used locally. In all cases to be effective, the limestone and related materials need to be finely ground to pass through a 100 mesh sieve. Lime when applied to peat soils is relatively immobile and a thorough mixing to the required depth is therefore important. This is laborious to achieve manually and even with mechanized means several diskings will be necessary. In the tropics, the low level of mechanization leads to inefficient liming at the field scale. Where deep mixing is necessary, split applications can be given, one half ploughed under, the other top dressed after ploughing. Split applications also allow the use of both pure and dolomitic limestone. 127

8.6 Fertilizer Use 8.6.1 Introduction 8.6.2 Burning 8.6.3 Basic principles 8.6.4 Nitrogen requirements 8.6.5 Phosphorus requirements 8.6.6 Potassium requirements 8.6.7 Calcium and magnesium requirements 8.6.8 Micro-nutrients or trace element requirements 8.6.9 Conclusions

8.6.1 Introduction One of the most important factors that has prevented large scale use of peat soils in the tropics is the very low chemical fertility. Oligotrophic peats, which areally are the most important in the tropics, are inherently poor in all plant nutrients. Eutrophic or mesotrophic peats, which are locally important, contain more nutrients than oligotrophic peats but they also need manuring or artificial fertilizers for commercial farming. This section concentrates on oligotrophic peats since their nutrient requirements have been studied in the tropics, particularly in Malaysia and Indonesia. Studies of the chemical fertility and nutrient deficiencies of peats have received more attention than either the more important physical changes of peat soils upon drainage, and the water management of drained peats. Nutrient deficiencies are easier to remedy than some of the detrimental physical changes caused by reclamation. The interest in the nutrient requirements of peats probably reflects the parallel interest in the case of mineral soils where it is often the most important constraint to improvement.

8.6.2 Burning Reclaimers and settlers of peatswamps realized the importance of fertilization of peat soils from the beginning. They initially fertilized by burning the peat, and this practice survives among traditional farmers employed in shifting cultivation. Kanapathy (1976 and 1977) has shown that burning is beneficial in increasing the pH value from 3.5 to occasionally over 5 which is desirable for food crops such as maize. Burning also adds potassium to the soil and changes unavailable phosphorus, stored in the organic compounds of the peat, into available forms. Other added benefits of burning include the increase in rate of decomposition caused by the rise in pH, producing an increase in nitrogen stored in the peat. Polak and Supraptohardjo (1951) demonstrated that heating peat to between 105 and 128°C produced a flux of ammonia, to which maize showed a marked response. Finally, burning releases copper compounds, usually fixed in peat, causing these soils to be frequently deficient in copper for most crops. The beneficial effects of peat burning are, however, short-lived and after only two years another burn is needed to support cropping. Regular burning leads to a rapid lowering of the peat surface, causing problems of waterlogging and often ultimately to abandoning agricultural activities. Where sustained agriculture is the aim, burning should be stopped, though at present it is often the only means available for the poor traditional farmer to maintain his subsistence agriculture. The regular use of fertilizer is the only way to sustain agriculture on these soils but ultimately however the peat will disappear (Chapter 7).

128

8.6.3 Basic principles Each crop has individual nutrient requirements and it is therefore difficult to discuss specific details. Instead an attempt is made to provide general fertilizer guidelines and principles for peat soils. Rates of fertilizer-use depend on both the cropping and type of peat present. Where there is no local research work available, the peat type needs to be identified and the specific requirements of the crop reviewed. Then it is possible to apply the results of research work done elsewhere to the local circumstances. Most information on fertilizer-use on tropical peats has either been carried out in the Everglades, Florida (eutrophic and mesotrophic peats), or on the oligotrophic coastal peats of Malaysia and Indonesia. Basic research on oligotrophic peats in temperate climates, particularly that on nitrogen, can also be applied to tropical peats. Admixtures of mineral material, which can be up to 50 percent of organic soils (Histosols) can have profound effects on the behaviour of peat soils. Extrapolation of research findings, particularly on fertility status, should never be attempted if the research results are not accompanied by an accurate analysis of the soils in question.

8.6.4 Nitrogen requirements The nitrogen status of peat soils is discussed in section 4.2, where it is shown that the total nitrogen content ranges widely because of differences in both the nature of peats and their decomposition rate. Generally, total N contents are high when compared with mineral soil. However, the amount of N available to the plant is important. While available N is indirectly determined by factors influencing the total N content other factors such as temperature, moisture, aeration and acidity play a role. The latter three affect the activity of soil organisms responsible for the breakdown of the organic compounds. The effect on soil N of liming Irish blanket bog soils decreased after a short time (O’Toole 1968). Chew et al. (1976a and b), in a study of the effect on nitrogen of liming oligotrophic peats under napier grass in Malaya, discovered an almost identical decrease in response to liming in the uptake of soil N. The availability of N is also affected in time by liming. This is because the easily decomposed nitrogenous components of the peats are mineralized first and relatively quickly after liming, leaving the less easily decomposed forms of organic N (Hardon and Polak 1941). Liming has the primary effect of raising the pH and any other effect on nitrogen liberation may be short-lived. The carbon/nitrogen (C/N) ratio of peat is important in assessing the available N content. In tropical organic materials C/N values lower than 16 are commonly regarded as indicative of soils where nitrogen stress will form a constraint to crop growth. However, temperature also plays a role. In temperate or colder regions available N varies with the season because of changing microbial activity. Available N content is also considerably influenced by drainage depth. In the Netherlands a drainage depth of 50 cm requires N-fertilization for good pasture growth whereas this is not necessary with deeper drainage. Likewise trials in the USA also indicated that no response to N fertilizer was found with deep drainage as opposed to a 10-67 percent yield increase, dependent on crop type, experienced when shallow drainage is practised (Table 27). It should be noted that nitrification proceeds rapidly under high temperatures and nitrite poisoning may affect forage crops. These, when consumed by ruminants, may in turn be responsible for nitrite poisoning and death of the animals.

129

Table 27 AVERAGE YIELD RESPONSE TO NITROGEN DRESSINGS ACCORDING TO DEPTH OF WATER-TABLE (source Lucas 1982) Crop

Years in test Water-table at 40 cm % Yield increase Water-table at 60 cm Water-table at 80 cm

Corn

7

43

6

2

Potatoes

4

67

9

4

Onions

5

23

3

2

Peppermint

5

10

6

3

General recommendations for the application of the nitrogen on peat soils to fit all conditions are difficult to give. Rates in the USA vary from 0-200 kg/ha. Generally more emphasis is given to phosphorus and potassium fertilization. From experimental work in Malaysia and Indonesia on many crops, it is agreed that nitrogen is required in quantity by all crops except legumes. A range of rates are specified but Tie and Kueh (1979) give the following rates of nitrogen application for oligotrophic lowland peats of South East Asia: Vegetables including long beans, French beans, green pepper and chilli - 280 to 560 kg/ha, cucumber - 560 kg/ha. Soya bean, groundnut and cowpea - 45 to 78 kg/ha. Maize - 180 kg/ha (on shallow peat with 20 percent mineral matter). Tapioca - 200 kg/ha. Tobacco - 140 kg/ha. Pineapple - 280 to 420 kg/ha (depending on variety). Oil palm appears to be negatively affected if ammonium sulphate is applied in dressings greater than 5 kg per tree. This quantity would also stimulate a high uptake of phosphate which is detrimental to the plant (Kanapathy 1978). Cattle manure or slurry is traditionally used as a fertilizer on pastures in the Netherlands. In Japan the application of farmyard manure or compost appears beneficial (Miyake 1982). In general, rice on peat soils receives rates of 40 kg/ha of nitrogen as it is assumed that the fertilizer acts as a starter in the initial growth stage and that large amounts of ammonium nitrogen will be released from the peat under submerged conditions (Miyake 1982). In conclusion, the application of nitrogen fertilizers to crops grown on peat is dependent on a great many variable factors. For each situation and type of peat rates should be carefully assessed by trial. However, it is important to note that, without adequate nitrogen the response to other supplied elements will be small. This is particularly the case with oligotrophic peats.

130

8.6.5 Phosphorus requirements The total phosphorus (P) content of tropical peat is generally low, but as is the case with nitrogen, we are more concerned with its availability. In oligotrophic peats in the tropics, available phosphorus content is generally larger than in upland soils. This is mainly caused by the low phosphate fixation experienced in these peats due to very low levels of Al and Fe. Most phosphorus is present in the organic form and upon mineralization this becomes readily available. Peats which have been drained and farmed for some time may increasingly develop phosphatefixing powers upon decomposition, because of a relative accumulation of Al and Fe compounds in the mineral admixture. For this reason added phosphate may become partly fixed. Available phosphorus values in peat soils are difficult to determine. This is an analytical problem inherent to the characteristics of organic soils. It is important to realize that each type of peat may require its own specific interpretation dependent on the extraction method used. The experience with oligotrophic peats in South East Asia indicates that phosphate requirements for most crops are not high. There can be considerable difference between deep and shallow peats. Perennials planted on peats less than 1 m thick may find their phosphorus source in the mineral subsoil. Type and depth of peat are therefore important variables. General recommendations are again difficult to make because of the large variability in conditions and crop demand, for example, pineapple requires less than one tenth of the amount of phosphorus than it requires of nitrogen that is 14-28 kg/ha. Tapioca one quarter of the demand for nitrogen, thus 50 kg/ha, whereas vegetables require more than half the nitrogen requirement. Table 28 gives the general phosphorus recommendations used for organic soils in the USA. Table 28 PHOSPHORUS FERTILIZER RECOMMENDATIONS FOR A RANGE OF CROPS BASED ON AVAILABLE SOIL PHOSPHORUS (source Lucas 1968) ppm of available soil phosphorus 1

Phosphorus recommended (kg/ha) 5

112

5

10

90

10

20

67

5

20

30

45

5

10

30

40

34

10

20

40

50

22

20

30

50+

60+

17

30+

40+

-

-

11

Blueberry

Alfalfa

Cabbage

Broccoli

Buckwheat Asparagus

Carrot

Cauliflower

Clover

Barley

Cucumber Celery

Grass

Bean

Endive

Onion

Oat

Corn

Lettuce

Tomato

Rye

Mint

Parsnip

Soya bean Pea

Potato

Pasture

Pumpkin

Radish

Sudan grass Spinach Turnip

Sugar beet

Wheat

Table beet

1

Extracted with 0.018-N-acetic acid, using one part air dried soil (by weight) with 10 parts of extracting solution 131

8.6.6 Potassium requirements Most peat soils, particularly the oligotrophic types, are deficient in potassium (K). While much of the K found in peat soils is readily available, once it is used up, K deficiency becomes severe. Traditional subsistence farmers try to supply the required potassium for food cropping by burning. As is the case with nitrogen, insufficient drainage affects potassium uptake. Shallow drainage aggravates the deficiency, and responses to K fertilizer are good. Experience in temperate climates with most crops grown on peat soils indicates that potassium is the most important nutrient for crop production. There are a number of important properties of potassium in relation to organic soils: i. K fixation, which is noticeable in many mineral soils, is absent. ii. Peat soils, although having a high cation exchange capacity, do not readily adsorb exchangeable K. iii. A large proportion of the total available K is always present in the soil solution and is therefore strongly mobile and prone to leaching. Losses therefore, can be substantial particularly under waterlogged conditions. It appears unwise to try to build up the K content of a soil by saturating the exchange complex as is often practised in mineral soils. In tropical peats, with high rainfall, potassium will be strongly leached. Tests for potassium requirement are therefore difficult, since potassium mobility appears to be much greater when high rates of K are applied to soils that test high in potassium. Fertilizer recommendations based upon soil tests must be modified to correct leaching, heavy rainfall or flood conditions. Some recommendations for vegetables on USA peat soils are given in Table 29.

132

Table 29 POTASSIUM FERTILIZER RECOMMENDATIONS FOR A RANGE OF CROPS BASED ON AVAILABLE SOIL POTASSIUM (source Lucas 1968) ppm of available soil potassium 1

1

Potassium recommended (kg/ha) 80

560

200

448

80

320

359

80

160

440

269

80

200

300

580

179

50

200

300

410

690

112

150

285

390

490

780

67

250

345

450

550

840

34

300

400

500

600

900

0

Barley

Bean

Alfalfa

Broccoli

Blueberry

Clover

Asparagus

Cauliflower

Grass

Corn

Cabbage

Onion

Oat

Mint

Carrot

Potato

Rye

Pea

Cucumber

Sugar beet

Pasture

Soya bean

Lettuce

Table beet

Wheat

Sudan grass

Parsnip

Tomato

Sweet corn

Radish

Turnip

Spinach

Celery

Extracted with 1-N-neutral ammonium acetate (1 part soil to 20 parts extract)

It should be noted that potassium requirements in temperate regions vary considerably with the crop. This is also the case in tropical crops, of which, particularly, tobacco, pineapple and legumes are highly demanding, and frequently in excess of nitrogen requirements. Because of the high potassium content in both the ash from fruit bunches of oil palm and from plant debris of crops such as sugar cane, it is good practice to return these materials to the land as a source of potassium fertilizer. Such materials also raise the pH. The liberal use of dolomitic limestone for correcting acidity increases the need for potassium to counteract the effect of high levels of magnesium. In such cases purer forms of limestone should, if possible, be used for liming.

8.6.7 Calcium and magnesium requirements Usually, calcium and magnesium are not deficient in tropical peats. Calcium deficiency is unlikely wherever the total Ca exceeds 0.5 percent. However, high levels of K, Na and/or NH 4 can induce Ca and Mg deficiencies. The Ca/Mg ratio can also influence deficiency, and even when the lower threshold value of 0.5 percent is surpassed, calcium deficiency can still develop. In coastal peats of South East Asia, where the magnesium contents are relatively high, this aspect is particularly important. Experimental evidence indicates that the benefits from liming are more a result of the increase in pH and the de-acidifying effects of this than to rectification of any calcium or magnesium deficiencies. 133

This is certainly the case with maize which requires a much higher pH than the usual value of 3.5 found in tropical oligotrophic peats. The relative growth of maize is therefore not a good indicator of the nutrient status of organic soils, although it is often used as such for mineral soils. Lim et al. (1973) advocate the use of grasses as indicators of nutrient status in organic soils though grasses can be insensitive to deficiencies in micro-nutrients.

8.6.8 Micro-nutrients or trace element requirements Copper, iron, boron, manganese, molybdenum and zinc have been shown to be deficient in organic soils for many crops. Copper Copper (Cu) deficiency, especially in cereals, has been reported to occur on peat soils throughout the world and tropical peats are no exception. The reclamation disease found in oats and rye grown on freshly reclaimed peat soils in Germany and the Netherlands in the late nineteenth and early twentieth centuries is well known. A similar failure to produce grains was found to occur in Indonesia and Malaysia (Polak 1941; Coulter 1957; Driessen and Sudewo 1977). Remarkably, only wet rice appeared to be affected and not dry rice. The cause of sterility is still not fully understood. Driessen and Sudewo (1977) tentatively attribute it to the presence of certain organic compounds, notably polyphenolic lignin degradation products, which hinder directly or indirectly (through copper fixation) one or more essential enzyme-catalyzed carbohydrate transformations. The fact that dry rice seems to be unaffected even when growing on the same peat on which wet rice shows severe deficiency, coupled with findings from Japan where drainage tends to cure the sterility (Miyake 1982), may indicate that wet conditions somehow appear to be related to the release of such toxic organic compounds. Ennis and Brogan (1968), have shown that humic acids are likely toxic compounds. In Malaysia, other crops as well as cereals, are prone to copper deficiencies; notably oil palm, sugar cane, tapioca and coconut (Kanapathy and Keat 1970). “Green die-back” commonly encountered in pineapple appears to be caused by Cu deficiency. The different response of plants to Cu is associated with the type of enzyme in the plant. Cereals respond to Cu because of the ascorbic acid oxydase which requires Cu in order to function in photosynthesis, whereas in forage crops the relationship between Cu and molybdenum content is important for livestock feeding. Molybdenum is taken up in toxic amounts when the Cu content is low and the molybdenum is higher than 3.0 ppm. It is difficult to assess the need for copper by soil analysis. Much depends on the method of extraction and total copper values are poor indicators. The need for copper can be predicted, to an extent, by the Cu content of the foliage. Under deficient conditions the content of the plant is usually less than 6 ppm (Lucas 1982). Copper deficiency can be corrected by several copper compounds but copper oxide and copper sulphate are mainly used in agriculture. Lucas (1982) recommends the use of about 10 kg/ha for low- and medium-response crops and 20 kg/ha for highly responsive crops. Oligotrophic peats in the tropics require larger quantities up to 35 kg/ha but this dosage will last for at least 5 years as the residual effect is good. The best method of application for wet rice is uncertain. Spraying of Bordeaux mixture (CuSO 4 -solution) in the generative phase of the wet rice is however promising.

134

Iron Iron (Fe) deficiencies arise in peats with a notably low Fe content. Its occurrence appears to depend partly on the crop. In many wet mineral soils Fe-content can become excessive due to reducing conditions but generally the oligotrophic peats in the tropics are so low in iron, particularly the centres of the peat domes, that iron deficiency is common in a range of crops including pepper, coffee, tapioca, grasses and legumes. Severe chlorosis is the common symptom. Iron deficiency can be overcome easily by foliar sprays of ferrous sulphate solution (0.5-1.5 percent w/w). Drilled iron sulphate at the rate of 50-100 kg/ha prevents chlorosis in cereal crops (Lucas 1982). Boron Boron (B) deficiency occurs in both alkaline and acid peats. It is commonly found in highly sensitive temperate vegetables such as cauliflower, beet and celery, but in the tropics boron deficiency is not so common. Alfalfa appears to be affected as also does oil palm and boron deficiency has been noticed in coffee (Tie and Kueh 1979). Deficiencies can easily be corrected by foliar sprays (sodium borate) of not more than 0.1-0.4 kg/ha of boron. Soil application of tetraborate effectively controls boron deficiency in oil palm. Manganese Manganese (Mn) deficiency in tropical peats is rare, because it very much depends on soil reaction. It is usually found only in eutrophic peats with a pH of over 5.5. Most tropical peats are oligotrophic, with a pH of less than 4.5, and frequently 3.5. Generally, manganese deficiency will therefore only occur after heavy liming. If this happens, it is easily corrected by applying manganese bearing materials as a foliar spray or mixed with other nutrients and broadcast at rates not exceeding 5 kg/ha of manganese. Another option is to acidify the soil with a sulphur compound. Molybdenum Molybdenum (Mo) deficiency is associated with soils of low pH (less than 5.5). Soils rich in free oxides are often deficient in available molybdenum. There are no reports on molybdenum deficiency on tropical peats in the literature studied. This may reflect the facts that tropical peats are commonly low in Fe and crops usually grown on peat soils are not Molybdenum-sensitive. Zinc Zinc deficiency is normally only apparent in soils with a pH greater than 6.5 or on peat soils which have been heavily limed. Large applications of phosphorus fertilizer and poor drainage can also induce zinc deficiency. As is the case with molybdenum there is no evidence that zinc deficiency is a problem in tropical peats.

8.6.9 Conclusions Trace element requirements are most pronounced for copper (nearly always) and iron (frequently). Although levels of other trace elements present few problems there is little detailed information and it is possible that, when more tropical peat is brought under cultivation and the crop range is extended, deficiencies not observed at present may develop. The likelihood of such development will depend largely on liming practices and fertilizer use. Over-liming should be avoided, a pH of 4.5-5.0 is adequate for most crops. Nitrogen and phosphorus applications should not be excessive. 135

8.7 Crop Protection 8.7.1 Weed control 8.7.2 Pest and disease control

8.7.1 Weed control Weeds enjoy the excellent growing conditions in peat soils and their abundance is a nuisance, particularly in freshly reclaimed peats. Weeds compete for space, light, moisture and nutrients and also act as hosts for pathogens, insects and nematodes. They reduce the quality and yield of crops and interfere with harvesting. Weed control therefore needs attention. In temperate regions weeds are removed either mechanically or by herbicides. Manual removal is costly, but in some cases it is necessary because either the crop is too dense to allow machinery or herbicides affect the quality of the crop. This is particularly the case with vegetable growing where yields of leafy vegetables may be affected by broadleaf weedkillers. Some of the most effective weedkillers are highly toxic which influences not only the crops grown but also the broader environment. Peat absorbs chemicals readily and undesirable toxicity can accumulate. The choice of effective weed controls is thus very much for the individual farm manger to decide, because the economics of each particular technique depends on local conditions and crop. In the tropics heavy weed infestation is also common. Wee, quoted by Tie and Kueh (1979), reports that weed infestation of pineapples on peat soils in Malaya decrease yields by 20-40 percent. For non-vegetable crops many weedkillers are effective but their use is often limited by economics. Crops on organic soils require larger applications of chemicals than those on mineral soils (2 to 3 times the amount given on mineral soils is not uncommon). The choice of the herbicide is important because many are short-lived. Pre-emergence types are more effective than incorporative ones. In most tropical countries, even in Malaysia where labour costs are relatively high, it is still cheaper to carry out weed control by hand than by other means.

8.7.2 Pest and disease control The control of soil-borne pests and diseases is particularly desirable on peat soils. In their natural state organic soils usually have low populations of anaerobic micro-organisms tolerant of the inherent acid conditions. Once the soils are drained, limed and fertilized an excellent medium is created for the rapid spread of new soil fauna and flora. Tie and Kueh (1979) indicate that many crops in the South East Asian peats are affected by fungal collar rot, root rot, white root and serious nematode attack. Bacterial wilt is common in crops such as chilli, tomato and ginger. There are several methods of controlling soil-borne diseases and pests. Fumigation and sterilization by gasses or steaming are used in the Netherlands in intensive systems of horticultural cropping (vegetables, potplants and flowers). High costs are a disadvantage and steaming and some fumigants such as dichloropropene, methyl bromide, methyl isothiocyanate and chloropicrin destroy a large proportion of the soil micro-organisms responsible for supplying available nitrogen to the plant. More nitrifying bacteria are killed than the ammonifiers and therefore a build up of ammonia can occur after fumigation, which retards some crops, particularly vegetables.

136

Crop rotation, including a clean fallow, can be effectively used against soil-borne pests such as nematodes. The use of flooding to combat soil pests was studied in Florida (Genung 1976) with remarkably good results. Table 30 illustrates the effect flooding had on important arthropods and oligochaetes. Both prolonged clean fallow and flooding caused evident reductions of populations of all the organisms including such predatory forms as Carabidae, Dermaptera, Formicidae and Chilopoda. Flooding under the 4-2-4 weeks alternation shows a much larger reduction of both soil pests and predators as well as oligochaetes than did either of two clean fallow treatments. The key factor in controlling pests by flooding appears to be the length of inundation. Soil-borne pests and diseases in tropical peats can probably be effectively controlled by flooding. Water control is one of the most important aspects of the agricultural management of peat soils and it is therefore often possible to artificially create floods to control pests. It is relatively cheap, highly effective, also eradicates some weeds, and unlike fallow systems no land has to be taken out of production. Table 30 INFLUENCE OF FLOODING AND CLEAN FALLOW ON ERADICATION OF MAJOR SOILBORNE PESTS (source Genung 1976) CWW = Corn wireworm

CW = Cutworms

SPWW = Sou. potato wireworm Cyd. = Cydniade W.Gbs. = White grubs

Cbd. = Carabidae

Swbg. = Sowbugs

Dmpa. = Dermaptera Pred. Dip. = Predatory Diptera

Ten. = Tenebrionidae Cent. = Centipedes

1

Olig. = Oligochaetes

White grub (Bothynus subtropicus Blatchley) mortality percentages under simulated flooding in a replicated and randomized laboratory trial was as follows: 0 hrs flooded (check) 5%, 24 hrs flooded 7.5%, 48 hrs flooded 25%, 72 hrs flooded 65%, 96 hrs flooded 95%.

137

9. ENERGY USE OF PEAT 9.1 Introduction 9.2 Peat as an Energy Source 9.3 Resource Estimation 9.4 Peat Production 9.5 Peat Extraction and Land Use Planning

9.1 Introduction Peat has been used as a form of energy for at least 2 000 years. It was useful as an alternative to firewood for cooking and heating in temperate and boreal regions of Europe, in particular Ireland, England, the Netherlands, Germany, Sweden, Poland, Finland and the USSR. The increasing use of gas and oil as cooking and heating fuels during the 20th century resulted in a diminishing use of peat for such domestic purposes. The high demand for electricity, however, locally stimulated the development of large electric power plants fuelled by peat. Peat appeared especially competitive in the 60-200 MW power plants which necessitated the reclamation of vast areas of peat for large scale peat extraction, particularly in Ireland, Finland and the USSR. Specialized technology was developed for these reclamation efforts. Recently, peat has been used for electricity generation in small units in the range of 20-1 000 kW. As well as these energy uses, peat is mixed with mineral soil in horticulture to increase the moisture holding capacity of sands, to increase the water infiltration rate of clayey soils, and to acidify soils for specific pot plants. Industrial uses include the extraction of valuable hydro-carbons (Table 31), and in the building industry it can be used as an insulator because of its poor heat conducting properties. Such uses are however relatively minor in relation to the large scale extraction for energy purposes on which this chapter concentrates. Extraction of peat for energy purposes as an alternative to relatively expensive imported fossil fuels such as oil and natural gas, has become particularly attractive to developing countries since the first fuel crisis in the nineteen seventies. There often appears to be a strong natural link between the extraction of peat for fuel and agricultural development. The latter either succeeds extraction when the peat deposits are exhausted or both enterprises are carried out simultaneously. It is likely that in the near future it will become possible to employ very small generators fuelled by peat for water control and water-table management in peatswamps used for agricultural purposes. If this can be done it would perhaps be economical and, from an incomegenerating point of view, desirable to stimulate integrated development of peatswamps. Peat extraction is only one land use option for peatswamps and often competes with other land use alternatives such as agriculture or preservation. In places peat extraction is desirable where the underlying mineral substrate is of good quality for arable use. The economic viability of peat as a fuel depends on local conditions including availability of other fuels, labour, material costs, transportation distances, climatic conditions and the possible scale of operation. Peat utilization can have socio-economic impacts on rural areas and this should be considered during the land evaluation process which includes future agricultural uses of reclaimed wetlands. A discussion of the issues in the development of peatswamps for extraction therefore forms part of this Bulletin.

138

The technology for peat extraction in the tropics is limited and must rely on the wealth of information from the developed countries, mainly in temperate regions, where peat extraction has been practised for centuries. For up to date technical information reference has been made to studies carried out by Ekono (1981), Bord-na-Mona (1984) and Euroconsult (1984 and 1985). The following sections describe the concepts and principles of evaluating the quality and quantity of peat resources, the planning of peat production, and finally the preparation of peatswamps for extraction and the related problems.

9.2 Peat as an Energy Source 9.2.1 Decomposition stage 9.2.2 Carbon and hydrogen content 9.2.3 Ash content 9.2.4 Types of fuel peat 9.2.5 Fuel properties 9.2.6 Minor factors

9.2.1 Decomposition stage Peats vary greatly in character partly depending on the state of decomposition of their plant remains and for this reason the Von Post scale of humification is commonly used to characterize peats (Table 16). Weakly decomposed peat is poorly suited to combustion, and therefore peat should be at least moderately decomposed (group H5) for use as a fuel. Table 31 IMPORTANT INDUSTRIAL USES OF PEAT AND RELATED PRODUCTION PROCESSES (source Euroconsult 1984) Raw material Well decomposed (milled peat, sod peat, briquettes)

Process

Primary products

Secondary products

Pyrolysis

Coke Tar Pyrolysis gas

Metallurgic coke Activated carbon Neutral oil Raw phenols Raw acids Raw alkalis

Gasification

Synthetic gas Water gas Generator gas

Oil products Hydrogen gas Methane Methanol Ammonia

Hydrogenation

Crude oil Gas

Oil products

Extraction

Raw waxes Raw resins Humic acid salts Peat residue

Synthetic waxes Fatty alcohols Fatty acids Humic acids

Oxidation

Organic acids Peat residue

Oxalic acid Higher organic acids

Hydrolysis products Peat residue

Food yeast Alcohol Furfural

Weakly decomposed (milled peat, sod peat) Hydrolysis

Chemical activation

Activated carbon

Heat treatment

Absorption materials

Purification, fertilization

Horticultural peat

139

9.2.2 Carbon and hydrogen content The carbon and hydrogen contents of peat are significant for its use as a fuel. During decomposition carbon and nitrogen typically increase whereas oxygen and hydrogen decrease (Table 32). However, relative amounts of the various organic compounds in peats such as carbohydrates, humic acids, lignin and bituminous materials (Table 12) affect the intensity of the three phases of combustion commonly distinguished in thermo-analytical studies.

9.2.3 Ash content Inorganic substances in peat deposits vary quantitatively as well as qualitatively and they affect the ash content which is a useful parameter when assessing the value of peat for fuel. Peats with a large content of mineral soil have a high ash value. The range of ash values in good quality peat is from 1-7 percent, but peats with values up to 14 percent are used for fuel. Analyses of some Indonesian peats are compared with those of peats from Finland and the Netherlands in Table 33. These figures show the wide range of ash values that can be present in the same areas, probably caused by admixtures of mineral soil. Table 32 THE MOST IMPORTANT ELEMENTS IN PEAT ACCORDING TO DEGREE OF DECOMPOSITION (source Ekono 1984) Element

Degree of decomposition according to Von Post Slightly decomposed peat H1-2

1

Moderately decomposed peat H5-6

Highly decomposed peat H9-10

Carbon

48-501

53-54

58-60

Hydrogen

5.5-6.5

5-6

5.0-5.5

Nitrogen

0.5-1

1-2

1-3

Oxygen

38-42

35-40

30-35

Percent weight in dry solids

Table 33 EVALUATION OF PEAT FOR FUEL PURPOSES (source Euroconsult 1984) 1

Moisture content is as received and is not representative of the bog as a whole. Dry basis. 3 Samples analysed by Shell Laboratories, Amsterdam. 4 Samples analysed by PPTM-Bandung. 5 Samples analysed by Ekono, Finland. 6 Ekono (1981). 2

Proportions of SiO 2 and Al 2 O 3 which raise the melting point of the ash often exceed 50 percent of the total ash content. CaO and Fe 2 O 3 tend to lower melting points. The sulphur contents of peat is usually low (0.1-0.4 percent as indicated in Table 34), although according to Table 13 values can be as high as 4 percent while Indonesian peats vary between 0.03 and 0.74 percent. Most peat therefore has a sulphur content comparable to oil which has a content of no more than 0.3-0.4 percent. This in turn is much lower than the sulphur content of coal and lignite (1-3 percent). Peat is therefore environmentally as acceptable as oil for use as a fuel.

140

Table 34 GENERAL CHEMICAL AND FUEL PROPERTIES OF A RANGE OF FOSSIL FUELS (source Lindström 1980) Coal

Lignite

Peat

Wood

Chemical composition Carbon (C)

weight %

76-87

65-75

50-60

48-55

Hydrogen (H)

weight %

3.5-5.0

4.5-5.5

5-7

6-7

Oxygen (O)

weight %

3-11

20-30

30-40

38-43

Nitrogen (N)

weight %

0.8-1.2

1-2

0.5-2.5

<0.6

Sulphur (S)

weight %

1-3

1-3

0.1-0.4

0.02-0.06

Volatile matter

weight %

10-50

50-60

60-70

75-85

Ash

weight %

4-10

6-10

2-15

0.1-2.0

Melting point of ash

°C

Fuel properties

Bulk density

1100-1300 1100-1300 1100-1300 1350-1450 3

kg/m

1

Effective calorific value of dry substance MJ/kg

728-880

650-780

300-400

320-420

28-33

20-24

20-23

17-20

1

1 MJ/kg = 239 Kcal/kg 1 MJ/kg = 430 Btu/lb

9.2.4 Types of fuel peat Three types of commercial peat are commonly distinguished: milled peat having a moisture content of 40-50 percent, air-dried sod peat with a moisture content of 30-40 percent and, artificially dried compressed peat briquettes with a moisture content of 10-20 percent. Milled peat is commonly produced by large scale mechanized peat extractions, whereas the other two are produced on a smaller scale by manual, semi-mechanical or mechanical methods, either in dry or in wet conditions. Milled peat is a heterogeneous mixture of loose peat particles which are cut from the surface of the peatswamp. The particle size, which varies with the production method, peat type and degree of decomposition, is between 3 and 8 mm. The peat is cut at 0.5-2.0 cm depth, spread uniformly across the surface of the peatswamp and allowed to dry in the wind and sun. Because of its low bulk density and relatively high moisture content, the calorific value of milled peat per unit volume is low, restricting its economic transport distance. Air-dried sod peat is a manually or mechanically compressed fuel. The size and shape of the product, which may be either cylindrical or brick shaped, is dependent on the production method. Hand-cut sod peat is about 125 x 125 x 300 mm (Plate 12), whereas mechanically produced sod peat is 10-30 cm long and 5-10 cm, in diameter. Compression takes place during production and the sods shrink further and harden during air-drying by the wind and sun. Air-dried sod peat has a higher calorific value per unit volume than milled peat and can therefore be transported more economically. Artificially dried and compressed peat briquettes or pellets are uniformly sized and thus easier to handle than either milled peat or sod peat. Milled peat is mechanically compressed to form the briquettes which are similar to bricks in size, whereas pellets are 3-30 mm according to the machine used. The milled peat raw material varies in moisture content from 40-55 percent and must be artificially dried to between 10 and 20 percent to produce either briquettes or pellets. The calorific value of both briquettes and pellets is high per unit volume and they can therefore be transported economically over longer distances than either sod or milled peat. Plate 12. Hand-cut sod peat from a trial in West Kalimantan, Indonesia 141

9.2.5 Fuel properties The combustion properties of commercial peats can be determined from their moisture content, their bulk density, their calorific value and their volatile substances. Table 35 lists these properties for the three forms of peat in comparison with wood and lignite. The moisture content of processed peats is variable and this influences their combustion properties and calorific values. Manufacturers try to keep stockpiles at a moisture content of 40-55 percent. Internal heating of the stockpiles usually starts at 50-100 cm depth and the moisture content can then drop to 10-20 percent. Internal heating can occasionally result in spontaneous combustion which can be prevented by cutting off the supply of oxygen either by covering with plastic sheets or by enlarging the stockpile. In the tropics internal heating and spontaneous combustion are considerable problems. The bulk density of milled peat is low and depends on the stage of decomposition of its fibres (86212 kg/m3 in Finnish peats). Compression which usually occurs on stacking is partly reversible when the weight is removed. The calorific value per unit volume of milled peat is in the range 3.35-4.19 GJ/m3 and is only one quarter to one sixth that of coal and about one tenth that of oil. The calorific value of peat dry matter is primarily dependent on the type of peat, degree of decomposition and ash content. Figure 30 illustrates the relationship between moisture content, ash content and calorific value. The calorific value of oven-dried peat is generally about 20 MJ/kg, but at the operating moisture content of 30-40 percent the calorific value is only about 10 MJ/kg. On this basis an estimate can be made of the total energy value of a peat deposit of known volume assuming a certain bulk density and field moisture content. For comparison the average effective calorific values of different fuels are given in Table 36. Table 35 COMBUSTION PROPERTIES OF PEAT, WOOD AND LIGNITE (source Ekono 1981) Peat

Wood

Lignite

Milled

Sod

Effective calorific value of dry matter (MJ/kg-mean)

18-22

18-22

18-22

18-19

20-24

Effective calorific value at operating moisture content (MJ/kg-mean)

7-12

11-14

17-18

12-13

11-14

Volatile substances (% dry matter-mean)

65-70

65-70

65-70

75-85

50-60

Bulk density at operating moisture content (kg/m3)

300-400 300-400

Operating moisture content (%)

40-55

30-40

Briquettes Biomass

700-800 10-20

In addition, the following factors which affect handling, should be considered: - flow properties - unwanted material (wood, minerals, fibres, etc.) - corrosive properties (acidity) - particle-size distribution

142

320-420 650-800 30-35

40-60

Figure 30. Relationship between moisture content, ash content and calorific value of peat (source Ekono 1981)

Table 36 AVERAGE EFFECTIVE CALORIFIC VALUES OF DIFFERENT FUELS (source Ekono 1981) Fuel

Moisture content in dry matter in operation

Bulk density

%

kg/m3

MJ/kg

GJ/m3

Peat briquettes

15

750

17.0

12.0

Peat pellets

15

750

17.0

12.0

Peat pellets

30

550

14.0

7.7

Milled peat

45

350

10.5

3.7

Sod peat

35

350

12.8

4.5

Crushed coal

9

800

25.0

20.0

Anthracite

5

870

29.3

25.4

Heavy fuel oil

-

950

40.6

39.0

Light fuel oil

-

950

42.7

41.0

143

Effective calorific value at operating moisture content

9.2.6 Minor factors Particle-size distribution and flow properties affect the fuel properties of peat. Optimum sizedistribution is not known but dust must be avoided as it creates unhealthy working conditions and may self-ignite. The proportion of the fine material in peat should therefore be low. On the other hand coarse fractions and fibric materials cause handling difficulties and therefore a high proportion of medium sized particles seems favourable. For this reason the best peats for fuel are probably those with moderate decomposition (mesic peats). Particle-size distribution should be considered in relation to bulk density and air space as large air spaces favour internal heating in the pile.

9.3 Resource Estimation 9.3.1 Initial survey

9.3.1 Initial survey Resources are estimated during an initial survey. When assessing the peat for energy purposes, the following properties should be assessed: degree of decomposition, depth, amount and size of wood fragments, nature of underlying deposits (with a view to land use after extraction) and feasibility of drainage. Samples are taken for analysis to determine the properties shown in Table 33. Loss on ignition should also be measured to help interpret the values obtained for ash content. While the physical conditions of the peat and the peatswamp are important considerations during the initial survey, assessment should also be made of factors such as the climate, accessibility, socio-economic and environmental impact of the extraction as part of the economic feasibility. Climatic data Peatswamps have to be drained prior to extraction and there needs to be adequate conditions for drying the peat production. Meteorological data on rainfall amounts and distribution, evaporation, sunshine hours and radiation, will show the best periods during the year for drying. In addition to the excess rainwater which must be drained from the peatswamp the equivalent of 180-190 mm of water must be evaporated from the drying beds during one drying period. Tropical areas, particularly those in the wet equatorial belt, have a high annual rainfall, often in excess of 3 000 mm, and there is no pronounced dry season with rainfall of less than 60 mm monthly. Nevertheless, peat can be dried quickly even under such a wet climate. Supardi (1983) found that under these conditions sod peat can be dried to a moisture content of 15-20 percent in a relatively short time (Fig. 31). Once irreversible drying sets in, which occurs within a few days, heavy rainfall has little effect on the peat sods. In Jamaica preliminary trials, however, indicated that a drying period of 30 days in the dry season was needed to reduce the moisture content from 90 percent to 35-40 percent. In the wet season, when 20-50 mm per day is not uncommon, it proved impossible to dry sod peat below 50 percent moisture (Robinson 1980). Climatic studies should therefore always be followed by field trials. Feasibility of drainage Many of the factors influencing the practicalities of drainage are studied during the initial survey. The outfalls through which drainage water will be removed require investigation as does the possibility of intercepting or damming external water and avoiding unwanted mineral sediments. These factors depend to a large extent on the water regimes of local rivers, creeks and swamps. The water regimes have to be analysed from hydrometric data and a hydrological evaluation of the terrain undertaken. On this evaluation depends whether a system of dry excavation or wet excavation (dredging) is adopted. 144

Accessibility Because of the large volumes of peat to be removed, accessibility is a more important consideration in peat extraction than in reclamation for agricultural development. In many cases access by water is the simplest method but the need for navigation should not interfere with water control measures. Roads serve a useful purpose but their construction is often difficult because of the difficulty of building foundations (see section 7.2). In mountain peats, roads are probably the best solution as there are sufficient quantities of earth-fill readily available. Post-extraction agricultural activities This factor is again emphasized because it is frequently forgotten in feasibility studies. In order to fully evaluate the site, information must be gathered on the potential agricultural suitability of the mineral substrate and the water regime that will prevail after peat extraction. Socio-economic consequences Problems of land tenure and resettlement before and after extraction need attention. In many countries peat extraction is legally regarded as mining and as such can cause land ownership problems. A possible influx of labour by migration of population must be given new employment once peat extraction is exhausted. These long term effects require proper evaluation. Environmental impact The environmental aspects of peatswamp development are an important part of any feasibility study and are dealt with in detail in Chapter 10.

9.4 Peat Production 9.4.1 Introduction 9.4.2 Clearing 9.4.3 Ditching 9.4.4 Clearing of stumps 9.4.5 Methods of production and layout

9.4.1 Introduction The raw peat which may contain as much as 95 percent water, must initially be drained to release as much free water as possible and to give sufficient bearing strength for the peat to carry men and machines. The peat surface is cleared of vegetation and is cambered to give run-off and to provide an area on which the processed peat can be dried by wind and sun. The spacing of the drains depends on the production method, but lies in the range 15-50 m. Drained bogs usually have a moisture content of 89-91 percent. When the peatswamp is sufficiently drained production can commence. In temperate regions this takes 5 to 7 years. Under a hot tropical climate the initial drainage period could possibly be much shorter. There is as yet little experience but there are indications that a 2 year drainage period might be sufficient.

145

Figure 31. Influence of rainfall on sod peat drying in West Kalimantan, Indonesia (source Supardi 1983) Traditionally peat has been cut by hand and was labour intensive. Mechanical production started in the mid-19th century when Hasselgren developed a moulding machine to improve sod peat quality. As greater quantities of fuel were required, technology was adapted and modified in the various peat producing countries to suit local climatic conditions and peat types. Today, while peat production is still carried out by hand locally, it is often a capital-intensive and highly mechanized process which is cheaper than either deep coal mining or oil production. Since the majority of tropical peats are mainly derived from trees and contain partly decomposed logs, branches and roots, the wood content is higher than in most temperate peats. Although wood content varies locally depending on the stage of decomposition of the peat, new mechanical methods of extraction will have to be developed for such materials. Preparation of peatswamps for extraction includes the following stages; surface clearance, ditching, clearing of stumps and the formation of the cutting area according to the extraction methods to be used.

9.4.2 Clearing All timber, including the crowns of trees, are gathered and removed by methods described in section 7.2. The trunks can be used for making the rafts for road foundations. Other woody materials can be made into chips if there is a local market. Burning should be avoided.

9.4.3 Ditching In most of Europe, the first stage in any peat development is drainage which is carried out by various types of ditchers. Usually 70 hp tractors are used with a ditching unit attached. The tractors often have tracks rather than wheels to reduce bearing pressure. Hydraulic excavators are used in both temperate and tropical countries. In Indonesia they are used in conjunction with manual cutting of hard timber fragments. Chain-saws, used widely for forest clearance can replace the hand-saw for these large logs. Although this method is slower and more labour intensive than the use of ditching machines, it is nevertheless equally successful. In general, the draining and ditching of tropical peats appear to be more difficult than in temperate countries. Often the machinery used is poorly adapted to tropical conditions. Some Burundi peats are exceedingly difficult to drain by conventional methods because the water levels of the main drainage outlets are often much higher than the bottom of the swamp to be drained. Pump drainage as developed in the Netherlands is needed.

9.4.4 Clearing of stumps The large amounts of contained wood (Plate 9) provide good fuel but where it is in large pieces it can damage the extraction machinery. Where peat is dug by hand this limitation does not apply, although the removal of large fragments from the fine-textured peat is very time consuming and may be prohibitively costly. Small trees and branches can be crushed into the peat layer to a depth of 40 cm using deep millers. This mechanized removal of wood on a large scale however is still to be tested under tropical conditions. Heavy timber can be removed by a “stumpdrag”, mounted on a digging machine. Such a drag can clear to one metre depth at a time. The large amounts of timber lifted from a tropical peat may cause storage and/or transportation problems if the materials cannot be used locally. Burning is not a satisfactory alternative.

146

During the nineteen twenties and thirties a system was developed in the USSR to produce “hydropeat” from bogs containing large amounts of wood. The system consisted of flushing the peat with pressurized water which transformed it into a viscous but fluid slurry. The slurry was carried or pumped to drying pans and spread out in a uniform layer of prescribed thickness. Peat sods were then made when the slurry dried. The system is no longer used in the USSR, but is still used in Sweden (Lindström 1980). In temperate countries there are wood shredding machines able to handle the woody peat. However, their efficiency in dealing with tropical peat containing bigger quantities of harder and larger fragments of timber must still be assessed.

9.4.5 Methods of production and layout The nature of the peat and the climate of the swamp are important factors to be considered when deciding on the method of extraction, the type of peat to be produced and consequently the size and layout of the extraction field. In tropical countries both climate and peat type differ from those in temperate regions where the extraction systems have been developed. Stockpiles of sod peat are commonly located where there is easy and economic access to them and hence the location changes as to whether the ground is frozen in winter or not. In Ireland storage systems are therefore different to those in Finland or the USSR where the climates are much colder. Dry sod production (dry extraction) Where sod peat is to be extracted by hand the development of the peatswamp is easy. It is important to install a drainage system usually with field drains at say 20 m intervals. It is sensible only to drain deeply (down to 1.50 m) in areas that will be excavated within about 5 years of drainage. Disregard of this rule enhances decomposition and the risk of fire. After completion of the initial field preparation for the first 5 years of extraction, drainage should be recommenced after about 3 years allowing 1 to 2 years for workable conditions to develop. After the first 1 m layer has been cut, it is possible to deepen the drainage and cut the second layer. Only where it is impossible to lower the water-table so that extraction must be done by dredging is it possible to waive provision of drainage 1 to 2 years ahead of excavation. Sod peat production can be carried out as described below and as shown in Figure 32, the tools used are illustrated in Figure 33. The surface layer of variable thickness (30-60 cm), commonly contains undecomposed roots and plant remains so is not suitable for sod peat production. It is therefore removed in strips one metre wide, and placed on the side of the secondary drain (Fig. 32B). Sod peat is then excavated with a special cutting tool producing a pre-arranged size of sod, generally about 40 x 10 by 10 cm thick. The cut sods are placed on top of the original surface layer placed on the side of the drain (Fig. 32C). When the one metre strip has been cut down to a depth of about a metre the next layer can be cut. When there is sufficient space created in the widening drain the original surface layer can be dumped at the bottom of the drain and the sod peat placed on this (Fig. 32D and E). Layers of sod peat should be loosely packed to allow air-circulation for rapid drying. This may take 4-5 months under temperate conditions but the experience in Rwanda has been that 2-2.5 months is enough. Local climate is of considerable importance but to speed up drying the piles can be turned after about 3 weeks. Mechanized systems of dry sod production are varied according to local conditions, and there is no experience of them in the tropics. Treatment here is therefore brief but a few principles must be given. Drainage should be installed about 2 years before excavation. Climate, especially rainfall, influences the length of this period. The surface layer must be removed as in the manual operated system but the surface must be levelled. The levelling can be done by the same machines which carried out the ditching. Extraction is usually carried out in strips 20-40 m wide, which are drained by open ditches 1.0-1.3 m deep. The peat should not be allowed to become too dry prior to excavation because it can slow or stop the machines. However, machines seldom have the power to cope with moisture contents over 83 percent. Peat should have a value greater than H5 on the Von Post scale. Well humified peat (H9 and H10) produces sods which crumble easily and therefore these peats, which produce excellent fuel, are best excavated by the milled peat system. 147

Mechanization requires high capital investment and is only cost-effective in large scale extraction. Production of 20 000 tons is possible in about 300 working days using machines which would take 30 000 man days manually. Removing wood fragments is the main constraint to mechanized production so the semi-mechanized field press system is probably the most feasible for tropical peats. In this system the peat is dug out by a hydraulic excavator and put into a towed field press machine powered by a 60-80 hp tractor which must have a crawler gear. The field press is towed by the tractor to a level storage area, away from the excavation site. While travelling, an agitator in the press, operated from the tractor power take-off, breaks up and macerates the peat. At the storage site a screw arrangement in the press, again operated by the power take-off, extrudes the peat through a rectangular orifice and spreads the sods on the ground behind. A sod marker marks off the sods into 375 mm lengths. The hydraulic excavator can if necessary be replaced by manual digging of the peat but in both cases timber must be removed. The woody nature of tropical peats may be the major constraint in peat production particularly for developing fully mechanized systems. Wet sod production In manually operated systems, shallow drainage is only required for preparing the drying site. The peat is dredged manually by using buckets or tins, the material is thereafter thoroughly mixed and spread over the drying beds in a layer 20-25 cm thick. After initial drying, the peat mass can be cut into blocks of required size and piled-up for further drying. This method requires a large area and is very labour intensive with about 100 kg of dry turf produced per man/day. In mechanized capital intensive systems, the traditional “bagger” is widely used. This excavates the peat to a depth of 2-7 m, macerates it and spreads it out to dry. Other methods include screw cutters, which excavate the peat with a 40-130 mm diameter screw cutter making a 400-1 000 mm deep angled cut into the surface. It macerates the peat and extrudes it behind the machine. Neither of these machines operates efficiently where the peat contains a lot of large hardwood fragments. Where this occurs major modifications are necessary. Disc cutters, however, use a disc 900-1 400 mm in diameter to excavate the peat from a 400-600 mm cut. They cut through wood and fibres and thus can be used on woody and fibrous deposits. The main constraint in fully mechanized wet production systems is the large drying areas required. A rule of thumb is that 1 tonne of dry peat needs 75 m2 of drying space under average drying conditions. Under ideal conditions the area needed is less (15 m2). Further, the peat should be of homogeneous quality and not contain clay lenses. Dry sod systems are therefore better suited to relatively small areas. Milled peat production This is a fully mechanized process involving: Milling The top 0.5-1.5 cm layer of peat is milled or pulverized in beds commonly 20-40 m wide but up to 3 km in length. Mixing The milled peat layer is mixed and turned by spoon harrows until the harvesting moisture of 40-50 percent is reached. The number of harrowings necessary obviously depends on the weather, 2-3 days is commonly sufficient, but in unstable weather it can take weeks. Ridging The milled peat is collected into one pile or ridge in the centre of each field.

148

Harvesting The peat is put into stockpiles. Three methods are used, the Peco, Haku and Harvester methods (Fig. 34).

a. In the Peco method, the peat is first collected into ridges along the length of the fields at 10-20 m intervals. The ridges are then moved sideways by a self-loading 10-20 m long transporter onto stockpiles at 100-400 m intervals. Stockpiles can be as long as 0.5-3.0 km, depending on the length of the fields, and are 4-6 m high but having a small crosssection of 20-40 m2. The milled peat can be transported to the margins of the bog by special vehicles or a narrow gauge railway. b. In the Haku method, the ridges are loaded by Peco type transporters on to bog trailers and carried to stockpiles which are often sited next to a road. These stockpiles can have a volume of 10 000-50 000 m3 with a height of 15 m. Because of tight compaction the temperature seldom rises over 50°C and the risk of fire or self-ignition is low. Tropical conditions will no doubt give a higher fire risk than that prevailing in temperate regions. c. The Harvester method uses self-loading trailers or harvesters to collect the peat and carry it to stockpiles at the end of the fields. Stockpiles are smaller, 6-8 m high and with a volume of 2 000-3 000 m3. Because the material is loosely piled there is a danger of internal combustion. The choice of harvesting method depends on the peatswamp, peat quality, demand and type of machinery available. Harvesting can also be carried out pneumatically and in this case 5-15 ton/ha can be harvested daily in thin layers from the dry upper part of the milled peat. The economic feasibility of each method should be assessed for each swamp individually. Milled peat is commonly used for fuelling large power stations of up to 120 MW and as a raw material for briquettes. The number of harvests a year depends on the climate. In Ireland, where there is an annual production period of 4-5 months there may be 12 harvests, while in Finland with a shorter but consistently drier production period 16 harvests may be collected. In the tropics there would undoubtedly be many more. In the experience of the author, good milled peat could be obtained after only 3 hours of intense drying in Kalimantan, Indonesia. The scale at which milled peat must be produced at these drying speeds is an obvious constraint. In contrast with manual and semi-mechanized sod peat production, which are labour intensive, milled peat production requires high capital investments. Manually-produced milled peat may be recommended in tropical regions where the supply and cost of labour is not limiting (Plate 13). The main constraints on milled peat production in the tropics are: a. Wood contents of up to 50 percent as in the coastal lowland oligotrophic peats of West Kalimantan, Indonesia. b. Unstable weather making mechanical harvesting uncertain. c. Self-combustion. In the tropics moisture content of the peat may fall below 40 percent, which may cause the peat to disintegrate into dust. This material can explode when reaching the power station.

149

Figure 32. Manual method of cutting sod peat (source Unger 1981)

150

Figure 33. Excavation tools for preparation of sod peat A. PEAT CUTTER

B. LIFTING SPADE

151

C. FLAT CUTTER

Figure 34. Production layout for milled peat according to the Haku and Peco stacking methods (source Lindström 1980)

152

9.5 Peat Extraction and Land Use Planning 9.5.1 Rapid disposal 9.5.2 Slow disposal 9.5.3 Effect of peatland distribution 9.5.4 Reclamation of freshly exploited peat deposits In connection with peat extraction there remain a number of issues to be discussed related to the planning of present and future utilization of peatswamps. Some brief remarks on the relevant basic considerations are made. Plate 13. Manually prepared milled peat on an experimental scale in coastal basin peat in West Kalimantan, Indonesia During the planning of peatswamp development choices have to be made between the various possible uses. Firstly, peatswamps can be reclaimed for agriculture, for peat extraction or for a combination of the two. Secondly, it is possible today to develop peatswamps for peat extraction followed by agriculture on the cut-over peatland. A third possibility is to opt for preservation in the natural state or to abandon the cut-over peatland and let it revert to near-natural conditions, and the possibility of renewed peat formation. Any plan using these options should be considered in relation to national economic factors. Extraction causes rapid diposal of peat. Under agriculture slow disposal is usual.

9.5.1 Rapid disposal The view is held that since peat will, in time, decompose, oxidize and disappear when used for agriculture, why not profit from it by excavating and selling it. Such views are justified if the underlying mineral substrate produces soils of excellent quality for agriculture, and present day economic factors are overruling. It is further justified if the peat is oligotrophic so that fanning will never be economic. However, the physical conditions of the cut-over peatswamp may be such that drainage required for agriculture will be difficult and costly to provide. Therefore before such a decision is taken the feasibility of these options should be carefully studied.

9.5.2 Slow disposal Extraction of peat will either be subsequently followed by agriculture or not depending on the nature of the underlying material and the hydro-topographic conditions prevailing after extraction. In the case of planned agricultural developments after excavation it is important to consider leaving a certain thickness of organic materials over the mineral substrate. This is particularly necessary when substrates are infertile sands. The incorporation of decomposed organic material into the coarse textured mineral materials will improve structure, water holding capacity, and general growing conditions. It may be advisable to opt for high water-tables to preserve the thin layer of peat on the mineral subsoil and in such cases land use has to be carefully chosen. In many of these cases pasture has to be recommended.

9.5.3 Effect of peatland distribution The natural conditions of peatswamps and their specific locations play a key role in decisions regarding possible land use. Peatland is often associated with remnants of river terraces underlain by infertile sands. In the tropical lowlands of South East Asia this combination is widespread. Coastal peats in lagoons often border infertile dune sands or old beach ridges. Peats here could be used as soil improvers and a peat excavation industry could be created. Transport costs though are high and it is doubtful whether peat contributes much to the fertility of these sands. Irreversible drying of the peat lumps if allowed would not improve structure, whereas oligotrophic peats would not improve the chemical fertility of the sands. Generally in small inland valley peatswamps, surrounded by infertile mineral soils, it is more economical to reclaim the swamps for fodder grass 153

and to use the manure produced by the cattle to fertilize and improve the soils of the neighbouring hills, than to excavate the peat and transport it to the hills. This kind of land-use planning attempts to integrate the potential of both the peatswamp and the adjacent land. Similarly, the large coastal lowland peatswamps of South East Asia are commonly fringed by thin peat and a belt of mineral materials forming river levees. A combination of agricultural activities on the mineral soils and shallow peat coupled with extraction of the peats thicker than 2 m is a possibility. The areas of deep peat after excavation to a minimum thickness of 1 m could be then used for agriculture or silviculture. The sustainability of drainage has an important bearing here. In countries with meagre resources of arable land the agricultural use of peatswamps should take precedence over peat extraction, particularly where located near large centres of population. In such cases valuable arable land is under pressure from urban and industrial sprawl.

9.5.4 Reclamation of freshly exploited peat deposits The reclamation of newly exploited and cut-over peats for agricultural use requires methods which are as yet untried under tropical conditions. In western Europe, cut-over bogs have been brought into cultivation for over a century, but most are of the high moor type where gravity drainage is no problem. Experience, however, indicates that it is highly desirable to leave at least 0.5-1.0 m of peat overlying the mineral substrate, or to incorporate this in the underlying mineral substrate. In the tropics lowland bogs are commonly underlain by potentially-acid sulphate materials, and the soils lack sufficient buffering capacity to neutralize the acids formed. Such conditions should be identified at an early stage in planning. The option to leave peatswamps untouched and in their natural state, or allowing them to revert to a natural state after peat extraction is more appropriately discussed in Chapter 10.

10. ENVIRONMENTAL ASPECTS OF RECLAMATION 10.1 Introduction 10.2 Natural Functions of Peatswamps 10.3 Environmental Impacts of Peat Reclamation

10.1 Introduction Previous chapters have indicated that peat has many uses. Only on a geological time scale can it be regarded as a renewable resource 1. Once extracted it can be used for many industrial purposes and is a raw material for the production of chemicals. However its most important uses are in agriculture and as an alternative source of energy. 1

Estimates of annual peat growth today vary between 0.5 and 1.0 mm and the subsidence rates of drained peat are of the order of 1.5-3.0 cm annually. Thus while the subsidence rate is 15 to 30 times the growth rate, peat cannot be defined as a renewable energy source. Technological developments make it increasingly more attractive to use peat and peat products as relatively cheap and clean fuel. It has a low sulphur and ash content whereas the carbon dioxide emitted to the atmosphere by combustion is about 10 percent lower than for coal (Table 34). Combustion is the conventional way to make energy from peat. However, new advances in thermochemical conversion (liquefaction) and biochemical conversion (anaerobic fermentation to methane) may make it possible to produce convenient fuels from peat, at a competitive cost, for heating or running internal combustion engines.

154

There is no question that, in the near future, peat will be increasingly used as a solid fuel on a large scale. This will be dependent on production and transport costs in relation to the prices of other fossil fuels such as oil, natural gas or coal. In the future peats will be increasingly used in the tropics for such purposes as soon as the reclamation methods have been developed. There is also the growing demand for arable land to feed the increasing population of many developing countries. Food cropping on the flat surfaces of reclaimed peatswamps is attractive in relation to the alternative steep hill sides where the risk of erosion seriously limits the cropping potential. The need to produce more food, augmented by the demand for more energy, creates the stimulus to reclaim the vast peat areas in the tropics which are often the last untapped land resources. It is unwise to ignore these demands and it is pragmatic to accept that the peatswamps will be increasingly exploited in the future for agriculture, including pasture, forestry and extraction. On the other hand environmentalists are warning against large scale exploitation and are attempting to preserve these unique ecosystems as much as possible. There is still time to ponder the question of what is the most sensible use of these natural resources. If peatlands are to be preserved, it is probably sensible for exploitation to go hand in hand with conservation. The following sections will stimulate thought and debate. Their aim is to provide information on the land use alternatives and options, on the basis of which rational decisions on resource planning can be taken.

10.2 Natural Functions of Peatswamps 10.2.1 Regulating functions 10.2.2 Production function 10.2.3 Information function 10.2.4 Miscellaneous functions A distinction is made between regulating functions, production functions, information functions and miscellaneous functions.

10.2.1 Regulating functions It is obvious that the peatswamps of the world play a significant role in the global cycles of carbon dioxide and water. The carbon cycle Peatlands developed during the last 10 000 years or so, constitute a large reservoir of carbon. The amount of carbon involved has been estimated by various sources, but the accuracy is dependent on the reliability of the assessment of global peat resources. Sjörs (1980) estimates the world content of carbon in peat to be in the order of 300 x 109 tons, whereas Moore and Bellamy (1974) arrived at a figure of 150 x 109. The latter was based on 230 million ha of world peat resources while present-day estimates are approximately 500 million ha; Sjörs values are therefore probably more realistic. Based on the fact that the atmosphere contains about 700 x 109 tons of carbon in the form of CO 2 , the deposition of carbon in peat has been an important, albeit very slow process. The accumulation rate is dependent on climate which showed much variation in post-glacial periods, the mid-postglacial period being least favourable. It is assumed by Sjörs (1980) that the world accumulation today of 90 x 106 tons yearly, based on climatic factors, is three times the average increment for the whole post-glacial period. Other authors give values of 210 x 106 tons per year, but their basic assumptions are probably incorrect. This Bulletin cannot cover this kind of discussion, nor be the arbiter but it should be noted that there are large discrepancies in the estimated values because of differences in basic assumptions. Sjörs indicates that the yearly world accumulation of carbon in the form of peat is very small in comparison with the estimated 100 x 109 tons annual ecosystemic world turnover of carbon. It is also much smaller than the annual 155

combustion of fossil carbon (coal, oil, natural gas and, as yet, only small quantities of peat) amounting to about 5 x 109 tons, and also of less importance than the transfer of carbon dioxide from the air to the slightly undersaturated sea, estimated at about 2.5 x 109 tons of carbon per year. It is concluded by Sjörs (1980) that although peatlands are a considerable long-term reservoir for carbon, their role for the short-term turnover of CO 2 is almost negligible. The global ecosystemic turnover of carbon would hardly be affected at all by destruction of the peatlands as accumulating ecosystems, other ecosystemic changes on earth being far more important. Winkler and DeWitt (1985) in discussing environmental impacts of peat extraction in the United States, look at the possible disruption of the global balance in carbon dioxide cycling if all peat resources were burned in a relatively short period. Studies of this nature must be supported by factual and quantitative information. Sjörs adheres to the view that it would seem out of the question that more than a fraction of the global peat resources would ever be exploited by man, since so much is virtually inaccessible, and even more, is economically unexploitable due to excavation difficulties and transport costs. It would also be economically unrealistic to use most peatlands for agriculture or forestry due to cool climate, low nutrient content and unsuitable, physical characteristics. Therefore, although burning peat contributes to the contemporary global rise in atmospheric CO 2 , its contribution will remain subordinate to that of other fossil fuels. Further, a substantial increase in the CO 2 content of the air by heavy burning of peat in situ is a theoretical possibility only. Moore and Bellamy (1974) have said that it is “speculative science fiction” to say that burning the 500 x 109 tons of peat resource will increase the “greenhouse” effect and alter the global climate. Resource planning must be based on hard facts and not this kind of speculation. Global climate Widespread drainage of peatlands for forestry, in temperate regions, decreases their comparatively high albedo, especially in winter. This effect would not be important in the tropics as peats are already forested in their natural state. However, a change to arable land after reclamation would have the opposite effect of increasing the albedo. This may have a local effect on climate but the climatic impact on a global scale is negligible. The hydrological function There is considerable evidence that peatswamps have an important regulating or controlling function on the hydrology of entire catchments. The main hydrological argument regarding the value of peatswamps is that peat acts as a reservoir, increasing the surface retention (storage capacity) of the landscape. Assessing their importance is difficult because of problems of quantifying the hydrological processes. In their natural conditions peatswamps act as a balancing reservoir smoothing the pattern of outflow during periods of heavy rainfall and drought (dry and wet monsoons). The reclamation of peat through drainage maintains the reservoir function and there will in fact be a greater controlling effect on run-off than in the undrained condition. The natural swamp is almost fully charged for most of the year otherwise conditions for peat growth would not exist. Drained peat can store more water initially and so control flash floods. However, drainage ultimately destroys the sponge effect of the peatswamp and the reservoir function is eventually lost. All these factors must be taken into account and carefully weighed if the “catchment control” argument is going to be used as a factor in land use planning. Adsorptive function Unmodified peat and peatland ecosystems can adsorb elements and compounds which have been released in toxic amounts into the environment. When peat is removed these adsorptive properties are lost and severe environmental degradation can result. Often heavy metals such as mercury, lead, cadmium, arsenic, zinc and selenium are tied up in peat deposits. Through the years the developing peat both adsorbs airborne and waterborne metals and then they are distributed in various ways throughout the peat. Peatswamps in this way act as natural filters in catchments. 156

Studies in Finland and Sweden have indicated that high levels of the heavy metals mercury and lead in lakes are attributable to the drainage of peatlands upstream. Likewise toxic selenium levels were found in ditches from drained peatlands in the western United States (Winkler and DeWitt 1985). The release of heavy metals upon drainage is of concern because they are toxic to many organisms. Toxicity is a matter of concentration and therefore the levels of heavy metals and their possible release through drainage and extraction should be studied in order to fully evaluate the environmental effects upon reclamation. For tropical countries such a precaution is especially necessary where proven deposits of heavy minerals occur in the country rock of catchment areas, or where the nature of the country rock gives reasons to suspect contamination with such metals. Burning peat containing concentrations of heavy metals also releases them into the environment. In this connection the adsorption of organic pollutants such as PCBs and other polycyclic hydrocarbons used in agriculture and for controlling pests and diseases, must be mentioned. These materials when used upstream may concentrate in the peatswamps downstream. Concentrations may become toxic when such peats are burned as turf. Very little is known about the cycling, life span and hazardous effects of these elements, but the role of peatlands as natural reservoirs of toxic deposits should be borne in mind and duly investigated. Peat holds concentrations of nutrients for varying lengths of time. These nutrients are released by peatland drainage and in North Carolina (USA) run-off from drained peatland had three times the nitrogen and 28 times the phosphorus concentrations found in run-off from undrained peatland (Winkler and DeWitt 1985). The sudden release of stored phosphorus from peat into surface waters can cause eutrophication of neighbouring lacustrine, riverine and estuarine systems. However, since most peats in the tropics are oligotrophic with very low concentrations of nutrients, their drainage water is almost sterile and eutrophication of surface waters is unlikely to occur. It could however arise in the case of eutrophic peats, and in peats which are easily fertilized and used for intensive agriculture such as vegetable growing. Buffering function In coastal areas the buffering function of peatswamps between the salt- and fresh-water systems is particularly important. The natural edge between fresh-water and salt-water marshes for example between Mangrove and Nipah swamps, is changed upon drainage and subsequent disruption of the peatswamp hydrology. This drainage results in the conversion of run-off from a non-pointsource from a natural peatland, to a point-source in drainage ditches, and contributes to the problems of already over-loaded estuarine ecosystems. Intrusion of salt-water into fresh-water wells in low-lying areas as well as fresh-water intrusion into delicately balanced salt-water estuary and deltaic ecosystems may occur. As a result of the latter, ecosystems essential to the survival of some forms of fisheries, such as shrimps, may be destroyed or irrepairably damaged. There are many examples of these risks. The hydrological and related buffering function of peatswamps is dictated by their location and position in the landscape. It is important to realize the natural function of peatswamps before decisions are taken to destroy them. It should be clear that where small interior valleys are concerned, the regulating functions operate within the watershed. Large coastal swamps, however, can also influence peripheral marine ecosystems and in general ecosystems beyond the confines of the water catchment, and impacts of reclamation can even be regional in scale.

157

10.2.2 Production function Peatswamps in their natural state are generally poor producers of food. Oligotrophic peats harbour few plants supplying food for fauna because of the very low fertility level of the environment. Fauna is therefore scarce and that which exists is specialized to survive under conditions of low food supply. Certain specialized plant species are of commercial value, such as the raffia palm and papyrus of some African swamps, supplying important raw materials for the local population. Natural forest products may therefore be important sources of income. Valuable timber such as Ramin and Merbau occur profusely in the coastal oligotrophic peatswamps of South East Asia. Although the products from natural peatswamps are generally of little importance their local value may be relatively significant.

10.2.3 Information function Peatswamps are unique ecosystems harbouring many species of flora and fauna not found elsewhere. It is difficult to evaluate the importance of the preservation of ecosystems with all their in-built genetic possibilities stored in the specialized bio-forms. However, history teaches us to be careful and not to waste nature’s capital stored in the genetic resources, and since reclamation will no doubt destroy much of this part of nature’s inheritance it would be wise to count the losses before embarking on ventures which may in the end cost more than preservation. A pragmatic and realistic approach would be to set aside sufficient area for preservation purposes to be decided upon by authorities competent in this field.

10.2.4 Miscellaneous functions Tropical peatswamps play an important and generally well-known role in the survival of migratory birds although this is not always acknowledged. The specific function which peatland plays is worth studying for tropical regions. From the general paucity in food one would surmise that the real oligotrophic peats of the coastal regions play a relatively minor role. Generally there are richer wetlands nearby which could be used, if needed. But as indicated there is little information to substantiate this. Peatswamps finally have a social function in that they often form areas for recreation, in particular near large concentrations of population. Although this function is not yet much developed in tropical countries, it is nevertheless a function which in some localities is an important alternative use.

10.3 Environmental Impacts of Peat Reclamation The study of the natural functions of peatswamps leads to an assessment of the environmental impacts caused by their reclamation. The following checklist which is not complete and does not cover all possible conditions may serve a useful purpose by indicating areas justifying attention: - toxic metal release from peat, - eutrophication of surface waters, - increased run-off water (disturbance of hydrological balance), - impacts on flooding and local fisheries, - release of organic pollutants, - changes of salt- and fresh-water systems, - changes in groundwater supply, - air pollution and fires. Added to these are impacts which are inherent to the removal of the swamp and the peat, namely: - loss of genetic resources (flora and fauna), - loss of production functions, - loss of the social function. 158

Most of these impacts have already been discussed above. A third set of impacts, the evaluation of which is difficult, because of their ambiguity, is formed by environmental changes which are both positive and negative. As an example environmental health may be mentioned. For centuries swamps have been drained and reclaimed because of their apparently poor living conditions. Incidence of malaria is often correlated with presence of swamps. This undoubtedly is true and draining the swamps may improve living conditions for the local people. It is, however, interesting to note that contrary to popular belief, peatswamps in their natural conditions are not necessarily a potent source of human disease. For example Beadle (1960) found that the two most important malaria carriers in Africa (Anopheles gambiae and A. funestus) do not breed in the interior of swamps though they are often found in open pools, footprints and other small hollows around the edges. An important factor which prevents some mosquitoes and not others from breeding in swamps, is the low concentration of oxygen in the peaty water. Larvae of A. gambiae have difficulty in surviving under anaerobic conditions. Shading is another factor that could deter egg laying. Peatswamps are therefore not always a potent source of malaria. Other swamps probably are. The problem of bilharzia (schistosomiasis) is rather different. Here, the snail Biomphalaria sudanica, which can carry Schistosoma mansoni, plays a major role as for example in Uganda. These snails have no difficulty in surviving under anaerobic conditions. They do not move very quickly nor spread far and the foci of infection are generally confined to small areas of water which people converge for washing and collecting water, or for fishing. Drainage of such swamps may result in the snails spreading over large areas and the impact of drainage on a variety of other diseases should be carefully assessed prior to reclamation. Sanitary health also warrants study. The settlement of people in peatswamps carries problems of supplying drinking water, and disposal of sewage. The settlement of people from hilly areas, used to running water, in an environment of stagnant water is accompanied by adaptation problems concerning disposal of human faeces. This can cause epidemics of gastro-enteritis and related diseases and the death of many children unaccustomed to the new environment. Likewise adults may die because of other diseases for which no natural resistance was built up. Both aspects deserve attention and therefore environmental impact studies are often needed if a full assessment of the consequences of draining a peatswamp is required. In fact it should form part of a feasibility study carried out prior to implementation of peatswamp development. It is strongly recommended that a broad environmental assessment is made in an early stage of planning. Often costly feasibility studies can then be forestalled. It could form part of the initial survey discussed in section 6.3. Such studies should be based on independent data. They should indicate present values and functions and their current (natural) sustainable potentials, together with the values and functions pertaining after large scale reclamation. Alternative uses and any mitigating measures should also be studied. Where development objectives are known and decided to meet demands it is realistic to search for and indicate other means by which these objectives could be met. If the objective is to investigate the potential of a peatswamp for agriculture because of pressure for arable land there may be other land nearby more or equally suited which could be used instead. Likewise, a demand for sources of energy may be met by indicating means other than reclaiming peatswamps. In the final analysis the various options on use should be carefully weighed on their merits so that a rational decision on land-use planning can be made. In conclusion, appropriate legislation is often lacking in many countries so that peatswamp development often proceeds without adequate initial investigation.

159

REFERENCES AND BIBLIOGRAPHY Ahmed, M.I. and Sim, E.S. 1976. Utilization of peat soil for sago palm cultivation in Sarawak. 3rd Asean Soil Conference, Kuala Lumpur. Ahti, E. 1984. Fertilizer-induced leaching of phosphorus and potassium from peatlands drained for forestry. Proceedings of the 7th International Peat Congress, Dublin 3:153-163. Allison, R.V. 1947. The significance of water conservation in the agricultural development of South Florida. Proceedings of the Florida State Horticultural Society 59:8-16. Amadieu, J. 1974. La culture maraîchère sur tourbe en pays tropicaux. Bulletin Agricole du Rwanda 7. Anderson, D.L. 1985. Sugarcane fertilization on muck and sand lands in South Florida. Research Report, EV-1985-6, University of Florida. Anderson, D.L. 1985. Crop soil fertility recommendations of the Everglades Soil Testing Laboratory. Research Report, EV-1985-10, University of Florida. Anderson, J.A.R. 1964. The structure and development of peat swamps of Sarawak and Brunei. Journal of Tropical Geography 18:7-16. Anderson M.S. 1968. Peat and muck in agriculture in the United States. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 2:625-630. HMSO, Edinburgh. Andriesse, J.P. 1974. Tropical lowland peats in South-East Asia. Royal Tropical Institute, Amsterdam, Department of Agricultural Research, Communication No. 63. Azevedo, A.L. 1954. The technology of peaty soils in Mozambique and Angola. Transactions of the 5th International Congress of Soil Science, Leopoldville 3:398-401. Baden, W. 1968. Combined utilization of bogs for crop and peat production. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 2: 801-808. HMSO, Edinburgh. Beadle, L.C. 1960. The swamps of Uganda. Shell Public Health and Agricultural News 3. Belkevich, P.I. and Chistova, L.R. 1968. Exchange capacity of peat with respect to alkali and alkaline-earth metals. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 2: 909-918. HMSO, Edinburgh. Beverly, R.B. 1981. Nutritional survey of the Everglades vegetable industry. Proceedings of the Florida State Horticultural Society 97:201-205. Boelter, D.H. 1968. Important physical properties of peat materials. Proceedings of the 3rd International Peat Congress, Quebec: 150-156. Boelter, D.H. 1969. Physical properties of peats as related to degree of decomposition. Proceedings of the Soil Science Society of America 33:606-609.

160

Boelter, D.H. 1974. The hydrologic characteristics of undrained organic soils in the Lake States. In: Histosols, their characteristics, classification and use (Ed. M. Stelly), Soil Science Society of America Special Publication No. 6:33-46. Boelter, D.H. and Blake, G.R. 1964. Importance of volumetric expressions of water contents of organic soils. Proceedings of the Soil Science Society of America 28:176-178. Bord na Mona. 1984. Fuel peat in developing countries. Study report for World Bank, Dublin. Bouman, S.A.M. and Driessen, P.M. 1985. Physical properties of peat soils affecting rice-based cropping systems. Proceedings of Workshop on Soil Physics and Rice, International Rice Research Institute: 71-83. Brown, J.L., Malterer, T. and Farnham, R.S. 1984. Surface and subsurface sampling of organic soils. Proceedings of the 7th International Peat Congress, Dublin. Burdine, H.W. and Guzman, V.L. 1965. The response of some green celery varieties to pH adjustment with sulphur on Everglades organic soil. Proceedings of the Florida State Horticultural Society 78: 148-155. Burdine, H.W. and Guzman, V.L. 1969. Celery cultivar responses to pH adjustment on Everglades organic soil. Journal of the American Society of Horticultural Science 94:520-523. Burdine, H.W. and Hall, C.B. 1974. Nitrate and nitrite content of carrots grown on the organic soils of the Everglades area of Florida. Proceedings of the Florida Soil and Crop Science Society 33:3436. Burdine, H.W. and Hall, C.B. 1976. Carrot responses to fertilizer levels on Everglades organic soils. Proceedings of the Florida State Horticultural Society 89:120-125. Burdine, H.W., Hall, C.B. and Hicks, J.R. 1977. Responses of some leafy vegetables to varying fertility levels on Terra Ceia Muck. Proceedings of the Florida Soil and Crop Science Society 36:46-51. Casselman, T.W. 1973. Response of open pit water level to water table fluctuations in Everglades organic soils. Proceedings of the Florida Soil and Crop Science Society 32:125-127. Casselman, T.W. and Green, V.E. 1972. Plastic lined mole drains in organic soils. Proceedings of the Florida Soil and Crop Science Society 31:12-15. Cassidy, J.C. 1973. Weed control in vegetables on peat soils. Scientific Horticulture 24: 68-72. Chateauneuf, J.J. 1981. Tourbes du Sénégal. Rapport de Mission d’Expertise. B.R.G.M. Orleans. Cheong, S.P. and Ng, S.K. 1977. Copper deficiency of oilpalms on peat. Proceedings of the Malaysian International Agricultural Oilpalm Conference, Kuala Lumpur, 1976. The Incorporated Society of Planters, Kuala Lumpur. Chew, W.Y., Joseph, K.T. and Ramli, K. 1978. Influence of soil-applied micronutrients on cassava (Manihot esculenta) in Malaysian tropical oligotrophic peat. Experimental Agriculture 14:105-111.

161

Chew, W.Y., Williams, C.N. Joseph, K.T. and Ramli, K. 1976a. Studies on the availability to plants of soil nitrogen in Malaysian tropical oligotrophic peat. I. Effect of liming and pH. Tropical Agriculture 53: 69-78. Chew, W.Y., Williams, C.N. and Ramli, K. 1976b. Studies on the availability to plants of soil nitrogen in Malaysian tropical oligotrophic peat. II. Effects of N.P.K. and micronutrients. Tropical Agriculture 53: 79-87. Clayton, B.S., Neller, J.R. and Allison, R.V. 1942. Water control in the peat and muck soils of the Florida Everglades. Florida Agricultural Experimental Station Bulletin No. 378, Gainsville, Florida. Cole, A.J. 1968. Grass production on cut-over raised bog-nitrogen, phosphorus and potassium requirements. Proceedings of the 3rd International Peat Congress, Quebec. Cole, A.J., Mulqueen, J. and Hammond, R.F. 1980. Effects of mixing cut-over raised bog peats and underlying sub-soils on the growth of carrots and clover. Irish Journal of Agricultural Research 19: 1-16. Cole, A.J., Murphy, W.E. and Poole, D.B.R. 1979. Effect of stocking rates and cobalt and copper supplementation on the performance of bullocks on shallow peatland. Irish Journal of Agricultural Research 18:195-209. Coulter, J.K. 1957. Development of the peat soils in Malaya. Malaysian Agricultural Journal 40: 188-199. Cox, R.S. 1957. Anthracnose, an undescribed disease of celery in the Everglades. Plant Disease Reporter 41:790-793. Darby, H.C. 1956. Drainage of the Fens. Cambridge University Press, Cambridge. Davis, J.H. 1946. The peat deposits of Florida, their occurrence, development and uses. Florida Geological Survey Bulletin No. 30. Deuse, P. Contribution à l’étude des tourbières du Rwanda et du Burundi. Rapport IRSAC (Treizième rapport 1960-64). Dolmat, M.T., Hassan, A.H. and Zakaria, Z.Z. 1982. Development of peat soil for oil palm planting in Malaysia - Johor Barat Agricultural Project as a case study. Palm Oil Research Institute of Malaysia Bulletin No. 5:1-17. Driessen, P.M. 1977. Peat soils. In: Soils and Rice. International Rice Research Institute, Philippines. Driessen, P.M. and Permadhy Sudewo. 1977. A review of crops and crop performance on Southeast Asian lowland peats. Bulletin No. 4, Soil Research Institute, Bogor, Indonesia. Driessen, P.M. and Rochimah, L. 1976. The physical properties of lowland peats from Kalimantan and their significance for land suitability appraisal. In: Research on peat and podzolic soils in Indonesia and their potential for agriculture. Soil Research Institute, Bogor, Indonesia.

162

Driessen, P.M. and Suhardjo, H. 1977. Reclamation and use of Indonesian lowland peats and their effect on soil conditions. 3rd Asean Soil Conference, Kuala Lumpur. Dryburgh, P.M. 1978. Scotland’s peat resources: an introduction to their potential. University of Edinburgh, School of Engineering. Dusky, J.A. 1982. Herbicides for celery, lettuce and carrots in the Everglades agricultural area. Proceedings of the Florida State Horticultural Society 95:339-342. Dusky, J.A. 1983. Weed management in celery in the Everglades agricultural area. Proceedings of the Florida State Horticultural Society 96:93-96. Dusky, J.A. 1984. Weed control in root crops grown on organic soils. Proceedings of the Florida State Horticultural Society 97:168-171. Ehrencron, V.K.R. 1949. Orienterende potproeven met zuur bosveen uit Borneo. Landbouw 21: 481-504. Ekono. 1981. Report on energy use of peat. Contribution to U.N. Conference on New and Renewable Sources of Energy, Nairobi. Ennis, M.T. and Brogan, J.C. 1968. Fixation of copper by humic acid. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 2:929-940. HMSO, Edinburgh. ESCAP. 1978. Proceedings of 3rd regional symposium on the development of deltaic areas, Bangkok. United Nations Publication, Water Resources Series No. 50, New York. Euroconsult. 1984. Etude de la maîtrise d’eau des sols tourbeux des périmètres Somalac dans la région du lac Alaotra et de l’entretien mécanisé des réseaux hydrauliques de ces périmètres. Repoblika Demokratika Malagasy, Entreprise Socialiste Somalac. Euroconsult/CESEN. 1985. Peat as a potential alternative source of energy. ADB Rural and Renewable Energy Development Study in Kalimantan. Euroconsult/DGIS. 1984. Preliminary assessment of peat development potential. Final Report. Republic of Indonesia/Kingdom of the Netherlands. FAO. 1973. The development of some soil fertility programmes in Mardi, Malaysia. Technical Assistance Report No. 3223. FAO. 1983. Guidelines: land evaluation for rainfed agriculture. FAO Soils Bulletin No. 52. FAO/Unesco. 1974. Soil map of the World, 1:5 million, 1: Legend. Unesco, Paris. Farnham, R.S. 1968. Classification of peat in the USA. Transactions of the 2nd International Peat Congress, Leningrad. (Ed. R.A. Robertson) 1:115-132. HMSO, Edinburgh. Farnham, R.S. and Finney, H.R. 1965. Classification and properties of organic soils. Advances in Agronomy 17:115-162.

163

Ferda, J. 1968. Reclamation of freshly exploited peat bogs. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 2:667-674. HMSO, Edinburgh. Fiskel, J.G.A., Mourkides, G.A. and Gammon, N. 1956. A study of the properties of molybdenum in Everglades peat. Proceedings of the Soil Science Society of America 20:73-76. Flaig, W. 1968. Uptake of organic substances from soil organic matter by plants and their influence on metabolism. In: Progress in Soil Biodynamics and Soil Productivity (Ed. A. Primavesi). Pallotti: Santa Maria, Brazil: 544-545. Floor, J. and Muyesu, C.C. 1986. Wetland soils in Kisii district, Kenya, and their suitability for agriculture and other types of land use. Proceedings of the 7th Annual Meeting of the Soil Science Society of East Africa, Arusha, 1985. Forsee, W.T. 1949. The effect of soil pH upon the growth of celery seedlings on the peat and muck soils of the Everglades. Proceedings of the Florida State Horticultural Society 62. Forsee, W.T. 1968. Crop production on peat and muck under subtropical conditions of the Florida Everglades. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 2: 697-704. HMSO, Edinburgh. Gascho, G.J. 1977. Silicon status of Florida sugarcane. Proceedings of the Florida Soil and Crop Science Society 36:188-191. Gascho, G.J. 1978. Response of sugarcane to calcium silicate slag. I. Mechanisms of response in Florida. Proceedings of the Florida Soil and Crop Science Society 37:55-58. Gascho, G.J. and Kidder, G. 1979. Responses to phosphorus and potassium and fertilizer recommendations for sugarcane in South Florida. University of Florida, Agricultural Experimental Stations, Bulletin 809. Genung, W.G. 1976. Flooding in Everglades soil pest management. Proceedings of Tall Timbers Conference on Ecological Animal Control by Habitat Management 6:165-172. Green, V.E. 1956. A survey of rice culture on organic soils. Proceedings of the Soil and Crop Science Society of Florida 16:334-351. GRONTMIJ. 1978. Mise en valeur et utilisation des sols tourbeux pour la théiculture dans régions montaneuses du Rwanda. Rapport d’une mission d’appui dans les régions de Cyohoha-Rukeri, Mulindi et Rugezi. République Rwandaise, Communauté Européenne. Guinazu, J.R. 1934. The peat deposits of the region of Fuego. Direc. Minoas y geol., Buenos Aires, Publication No. 10. Guzman, V.L., Burdine, H.W., Harris, E.D., Orsenigo, J.R., Showalter, R.K., Thayer, P.L., Winchester, J.A., Wolf, E.A., Berger, R.D., Genung, W.G. and Zitter, T.Z. 1973. Celery production on organic soils of South Florida. Agricultural Experimental Stations, University of Florida, Bulletin No. 757. Hammond, R.F. 1971. Survey of peat deposits on Makandudu, Milandu and Forkaidu Islands in Miladummandulu, North Atoll. Report to the Government of the Maldives. FAO TA3013. 164

Hammond, R.F. 1981. The Peatlands of Ireland. Soil Survey Bulletin No. 35, An Foras Taluntais, Dublin. Hanrahan, E.T. 1984. Peat drainage - the consolidation analogy. Proceedings of the 7th International Peat Congress, Dublin 4:205-214. Hardon, H.J. and Polak, B. 1941. De chemische samenstelling van enkele venen in Nederlandsch Indië. Landbouw 17:1081-1093. Harrison, D.S., Speir, W.H. and Thomas, F.H. 1941. Installation and operation of a set of watertable plots on an organic soil. Transactions of the American Society of Agricultural Engineers 6, (1): 3-5. Helenelund, K.V. and Hartikainen. 1972. In site measurements of undrained shear strength of peat by helical auger tests. Proceedings of the 4th International Peat Congress, Espoo. Helenelund, K.V., Lindqvist, L.O. and Lundman, C. 1972. Influence of sampling disturbance on the engineering properties of peat samples. Proceedings of the 4th International Peat Congress, Espoo. Hendrick, E. 1984. Drainage of peat lands for afforestation. Proceedings of the 7th International Peat Congress, Dublin 3:304-315. Hidding, A.P. 1982. The use of peat and peat soils for horticulture. In: Proceedings of the symposium on peat lands below sea level (Eds. H. de Bakker and M.W. van den Berg). International Institute for Land Reclamation and Improvement. Publication No. 30:248-255. Hooghoudt, S.B., van der Woerdt, D. and van Dijk, H. 1960. A physico-chemical investigation into the causes of the irreversible drying of peat soils and the possibilities of improvement. In: Irreversibly drying peat soils in the west of the Netherlands. By Hooghoudt, S.B., van der Woerdt, D., Bennema, J. and van Dijk, H. Versl. Landb. Ondrz No. 66:23, Wageningen. Hortenstine, C.C. and Forsee, W.T. 1960. Research and application of soil testing for organic soils. Proceedings of the Florida Soil and Crop Science Society 20: 363-370. Igarashi, Y., Akazawa, T., Matsushita, K. and Umeda, Y. 1984. Soil characteristics and geohistory on the Ishikari peatlands, Northern Japan. Proceedings of the 7th International Peat Congress, Dublin 1: 205-219. ILACO. 1966. Report on the soil investigations in the Niger Delta Special Area. NEDECO/ILACO, Kingdom of the Netherlands. ILACO. 1977. Yala swamp investigation project, final report. Republic of Kenya, Ministry of Agriculture and National Irrigation Board, Kingdom of the Netherlands. ILACO. 1978. Land Evaluation with a view to reclamation of the Serba hurta and Kuo swamp areas, Sumatera, Indonesia. Plantagemaatschappij Serbahuta Ria, Medan. Ingram, R.L. 1984. The bulk density of North Carolina peats, (USA). Proceedings of the 7th International Peat Congress, Dublin 4:237-247.

165

Jongerius, A. and Pons, L.J. 1962. Soil genesis in organic soils. Boor en spade 12: 156-168. Kalmari, A. 1982. Industrial peat program in Burundi carried out by Ekono. Seminar on Peat for Energy Use, Bandung, Indonesia. Kanapathy, K. 1976. Fertilizer requirement on peat soils. Malaysian Agricultural Journal 50:292307. Kanapathy, K. 1978. Planting oil palms on peat. Perak Planters Association Journal: 101-107. Kanapathy, K. and Keat, G.A. 1970. Growing maize, sorghum and tapioca on peat soils. Proceedings of a Conference on crop diversification in Malaysia: 26-35. Karesniemi, K. 1972. Dependence of humification degree on certain properties of peat. Proceedings of the 4th International Peat Congress, Espoo. Kivinen, E. 1980. Proposal for general classification of virgin peat. Proceedings of the 6th International Peat Congress, Duluth: 47-51. Kivinen, E. and Pakarinen, P. 1980. Peatland areas and the proportion of virgin peatlands in different countries. Proceedings of the 6th International Pea Congress, Duluth: 52-54. Knecht, T. 1982. Estudo preliminar sobre as ocorrencias de turfa no vale do ribeira de Iguape, Sp., Brasilia. Revistu do Instituto Geografico e Geologico, Sao Paulo 3:5-14. Kueh, H.S. 1972. A review of agronomic results of experiments at Stapok Peat Experiment Station from 1966 to 1971. Department of Agriculture, Research Branch, Sarawak, Malaysia. Kurbatov, I.M. 1968. The question of the genesis of peat and its humic acids. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 1:133-137. HMSO, Edinburgh. Lassoudière, A. 1976. Banana cultivation on hydromorphic soils of the Agneby Marsh in Ivory Coast. Proceedings of the 5th International Peat Congress, Poznan 3:104-110. Laurent, M.F., Shih, S.F. and Snyder, G.H. 1983. Stopping subsidence with aquatic crops. Institute of Food and Agricultural Sciences, University of Florida. Lim, C.K., Chin, Y.K. and Bolle-Jones, E.W. 1973. Crop indicators of nutrient status of peat soil. Malaysia Agricultural Journal 49:198-207. Lindström, O. 1980. The technology of peat. Ambio 9: 309-313. Lucas, R.E. 1968. Plant nutrient requirements for crops grown on organic soils. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 2:781-794. HMSO, Edinburgh. Lucas, R.E. 1982. Organic Soils (Histosols). Formation, distribution, physical and chemical properties and management for crop production. Michigan State University, Research Report No. 435 (Farm Science). Maas, E.F., Tie, Y.L. and Lim, C.P. 1979. Sarawak land capability classification and evaluation for agricultural crops. Technical Paper No. 5. Soils Division, Department of Agriculture, Sarawak, Malaysia. 166

Maclean, A.J., Halstead, R.L., Mack, A.R. and Jasmin, J.J. 1964. Comparison of procedures for estimating exchange properties and availability of phosphorus and potassium in some eastern Canadian organic soils. Canadian Journal of Soil Science 44:66-75. Maltby, E. 1986. Waterlogged wealth. Earthscan, London and Washington D.C. McCall, W.W., Davis, J.F. and Lawton, K. 1956. A study of the effect of mineral phosphates upon the organic phosphorus content of organic soil. Proceedings of the Soil Science Society of America 20:81-83. McDonnell, J.G. and Farrell, E.P. 1984. An evaluation of techniques for the measurement of decomposition of peat Proceedings of the 7th International Peat Congress, Dublin 4:358-382. McGreevy, J.M. and Farrell, E.P. 1984. The influence of lime on some decomposition characteristics of Irish peats Proceedings of the 7th International Peat Congress, Dublin 3:418441. McNally, G. 1984. Peatland reclamation. Proceedings of the 7th International Peat Congress, Dublin 4:446-450. Mehlich, A. 1942. The significance of percentage base saturation and pH in relation to soil differences. Proceedings of the Soil Science Society of America 7:167-174. Miyake, M. 1982. Improvement and management of peat soils in Japan. In: Tropical Agriculture Research Series No. 15. Tropical Agriculture Research Center, Ibaraki, Japan. Mohr, E.C.J. and van Baren, F.A. 1954. Tropical soils. Van Hoerve, The Hague. Mohrmann, K.J.M. 1952. Reclaimed peat soils and their agricultural importance. Soil Science 74:57-68. Moorman, F.R. and Santhad Rojanasoonthan. 1968. The Soil Map of Thailand. Proceedings of the 3rd Malaysian Conference, Kuching, Sarawak. Moore, P.D. and Bellamy, D.J. 1974. Peatlands. Elek Science, London. Morrison, T.M. and Caughley, J.R. 1960. Fertilizer requirements in an acid peat. New Zealand Journal of Agricultural Research 3:1-5. Morton, J.F. and Snyder, G.H. 1976. Aquatic crops versus organic soil subsidence. Proceedings of the Florida State Horticultural Society 89:125-129. Morton, J.F. and Snyder, G.H. 1978. Trial of water celery as an aquatic flavoring herb for Everglades farmlands. Proceedings of the Florida State Horticultural Society 91:301-305. Morton, J.F., Snyder, G.H. and Oele, E.A. Wild Rice 1980. - A promising gourmet crop for the Everglades. Proceedings of the Florida State Horticultural Society 93:273-278. Murashko, A.I. 1969. Compression of peat bogs after draining. In: Land subsidence 2: 535-546. IAHS-AIHS Publication No. 89:535-546.

167

NEDECO. 1961. Report on the feasibility of diking and draining the peat exploitation areas in the Ganges Delta and some agricultural aspects of the scheme. Ng, T.T. and Ahmed, M.I. 1971. Nutrient status assessment of a Sarawak deep peat. Department of Agriculture, Research Branch, Sarawak, Malaysia. Nichols, D.S. 1980. Nutrient removal from wastewater by wetlands. Proceedings of the 6th International Peat Congress, Duluth: 638-642. Nieminen, M., Ranta, J., Moilanen, A. and Lappi, M. 1984. A basis for the classification of peat for fuel use. Proceedings of the 7th International Peat Congress, Dublin 2:421-432. O’Hair, S.K., Snyder, G.H. and Morton, J.F. 1982. Wetland Taro: a neglected crop for food, feed and fuel. Proceedings of the Florida State Horticultural Society 95:367-374. Okruszko, H. 1984. Agricultural utilization of peatlands. Proceedings of the 7th International Peat Congress, Dublin 4:451-454. O’Toole, M.A. 1968. Lime requirements for pasture establishment on blanket peat. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 2:743-753. HMSO, Edinburgh. Ozaki, C.T. 1955. Phosphorus and potassium requirements of Blackeye Peas grown on Everglades peaty muck soil. Proceedings of the Florida Soil and Crop Science Society 15:49-52. Paivanen, J. 1984. Peatland Forestry. Proceedings of the 7th International Peat Congress, Dublin 4:455-465. Pate, F.M. and Snyder, G.H. 1978. Effect of high water table in organic soil on yield and quality of forage grasses-Lysimeter study. Proceedings of the Florida Soil and Crop Science Society 38:7275. Pate, F.M., Allen, R.J. and Crockett, J.R. 1980. Fertilization of Roselawn St Augustinegrass pasture on organic soil. University of Florida, Agricultural Experimental Stations. Bulletin No. 811. Paul, H. 1954. Phosphorus status of peat soils in British Guiana. Soil Science 77:87-93. Phillips, N. 1985. The Everglades experience; sixty years of progress. EREC Research report, University of Florida. Polak, B. 1941. Veenonderzoek in Nederlandsch Indië. Landbouw 17:1033-1062. Polak, B. 1950. Occurrence and fertility of tropical peat soils in Indonesia. Proceedings of the 4th International Congress of Soil Science 2:183-185. Polak, B. and Supraptohardjo, M. 1951. Pot and field experiments with maize on acid forest peat from Borneo. Contributions from the General Agricultural Research Station, Bogor No. 125. Pons, L.J. and Driessen, P.M. 1975. Reclamation and development of waste land on oligotrophic peat and acid sulphate soils. Proceedings of Symposium on development of Problem Soils in Indonesia, Jakarta. 168

Portères, R. 1950. Terres organiques tourbeuse de l’ancien delta de l’Agneby (Côte Ivoire) et leur conduite en culture bannanière. Agronomie Tropicale 5:268-291. Pyavchenko, N.I. 1968. Basic terminology in bog science. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 1:111-114. HMSO, Edinburgh. Rahi, G.S., Shi, S.F. and Myhre, D.L. 1978. Calibration and sensitivity of neutron moisture probe for Histosols. Proceedings of the Florida Soil and Crop Science Society 38:87-90. Rahi, G.S. and Shih, S.F. 1980. Soil-water characteristics of Histosols as related to water table depth. Proceedings of the Florida Soil and Crop Science Society 39:34-37. Raleigh, G.J. and Guzman, V.L. 1980. Shawnee. A crisphead lettuce adapted to organic soils of Florida. University of Florida. Agricultural Experimental Stations. Circular S-269. Ravikovitch, S. 1948. Peat soils and soils rich in organic matter in the Huleh Valley, Israel. Agricultural Research Station, Bulletin No. 47, Rehovot. Raymond, G.P., Wood, E.A. and Hollingshead, G.W. 1972. Consolidation of undisturbed fine fibrous peat. Proceedings of the 4th International Peat Congress, Espoo. Reynders, J.J. 1962. A brief report on the occurrence of peat in Netherlands New Guinea. Boor en Spade 12:27-32. Robinson, E. 1980. Peat as a fuel resource in Jamaica, West Indies. Proceedings of the 6th International Peat Congress, Duluth: 88-91. Roche, P. 1952. Les sols de marais récemment récupérés au Lac Alaotra. Agronomie Tropicale 7:43-63. Roldán, J. 1959. Fertility status of organic soils in Puerto Rico. Journal of Agriculture of the University of Puerto Rico 43:255-267. Rypácek, V. 1968. Humic acids as related to plant morphogenesis and toxicity. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 2:725-729. HMSO, Edinburgh. Schnitzer, M. and Hoffman, I. 1966. A thermogravimetric approach to the classification of organic soils. Proceedings of the Soil Science Society of America 30:63-66. Schothorst, C.J. 1977. Subsidence of low moor peat soils in the Western Netherlands. Institute for Land and Water Management Research, Wageningen. Technical Bulletin No. 102. Schothorst, C.J. 1982. Drainage and behaviour of peat soils. In: Proceedings of the symposium on peat lands below sea level (Eds. H. de Bakker and M.W. van den Berg), International Institute for Land Reclamation and Improvement. Publication No. 30:130-163. Schwerdtfeger, G. 1980. Comparison of peatland-classification in different national systems of soil science. Proceedings of the 6th International Peat Congress, Duluth: 93-95. Shih, S.F. 1980. Impact of subsidence on water management in Everglades agricultural areas. Proceedings of the 6th International Peat Congress, Duluth: 473-476. 169

Shih, S.F. and Rahi, G.S. 1981. Seasonal Variations of Manning’s Roughness Coefficient in a subtropical marsh. Transactions of the American Society of Agricultural Engineers 25: (1); 116119. Shih, S.F., Asce, M. and Snyder, G.H. 1982. Water Control and Cropping Alternatives in Everglades. Proceedings of the Special Conference on Environmentally Sound Water and Soil Management, American Society of Civil Engineers, Orlando. Shih, S.F., Stewart, E.H., Allen, L.H. and Hilliard, J.W. 1979. Varibility of depth to bedrock in Everglades organic soil. Proceedings of the Florida Soil and Crop Science Society 38:66-71. Shih, S.F., Vandergrift, D.E., Myhre, D.L., Rahi, G.S. and Harrison, D.S. 1981. The effect of land forming on subsidence in the Florida Everglades’ organic soil. Proceedings of the Soil Science Society of America 45:1206-1209. Shoham, D. and Levin, I. 1968. Subsidence in the reclaimed Hula swamp area of Israel. The Israel Journal of Agricultural Research 18:15-18. Sjörs, H. 1980. Peat on Earth: multiple use or conservation? Ambio 9:303-308. Skaven-Haug, S.V. 1972. Volumetric relations in soil materials. Proceedings of the 4th International Peat Congress, Espoo. Smith, G.D. 1965. Lectures on soil classification. Pedologie Special No. 4: 1-135. Snyder, G.H., Burdine, H.W., Crockett, J.R., Gascho, G.J., Harrison, D.S., Kidder, G., Mishoe, J.W., Myhre, D.L., Pate, F.M. and Shih, S.F. 1978. Water table management for organic soil conservation and crop production in the Florida Everglades. University of Florida, Agricultural Experimental Stations, Bulletin No. 801. Snyder, G.H., Morton, J.F. and Genung, W.G. 1981. Trials of Ipomoea aquatica, nutritious vegetable with high protein- and nitrate- extraction potential. Proceedings of the Florida State Horticultural Society 94:230-235. Soepraptohardjo, M. and Driessen, P.M. 1976. The lowland peats of Indonesia, a challenge for the future. In: Research on peat and podzolic soils in Indonesia and their potential for agriculture. Soil Research Institute, Bogor, Indonesia. Soil Survey Staff. 1975. Soil Taxonomy - a comprehensive system. U.S.D.A. Sokolov, B.N. 1976. Principal trends in the utilization of peat deposits and peat in the USSR. Proceedings of the 5th International Peat Congress, Poznan: 244-254. Stephens, J.C. 1956. Subsidence of organic soils in the Florida Everglades. Proceedings of the Soil Science Society of America 20:77-80. Stephens, J.C. 1969. Peat and muck drainage problems. J. Irrigation and Drainage Division, Proceedings of the American Society of Civil Engineers 95, (IR2): 285-305.

170

Stephens, J.C. 1974. Subsidence of organic soils in the Florida Everglades - a review and update. In: Environments of South Florida: Present and Past. Memoir 2, Miami Geological Society. Stephens, J.C. 1983. Organic soil subsidence. LH Allen. Stephens, J.C. and Johnson, L. 1951. Subsidence of peat soils in the Everglades Region of Florida. Contribution Division of Drainage and Water Control, Soil Conservation Service. Stephens, J.C. and Speir, W.H. 1969. Subsidence of organic soils in the USA. In: Land Subsidence 2:523-534. IAHS-AIHS Publication No. 89. Stephens, J.C. and Stewart, E.H. 1977. Effect of climate on organic soil subsidence. In: Proceedings of the 2nd Symposium on land subsidence, Anaheim, California. 1976 IAHS-AIHS Publication No. 121:647-655. Stephens, J.C., Allen, L.H. and Chew, E. 1984. Organic soil subsidence. American Geological Society Reviews in Engineering Geology VI:107-122. Subagyo, and Driessen, P.M. 1972. The ombrogenous peat soils of Indonesia. Soil Research Institute, Bogor. Suhardjo, H. and Widjaja-Adhi, I.P.G. 1977. Chemical characteristics of the upper 30 cm of peat soils from Riau, Sumatra (Indonesia). In: Final Report, Agricultural Technical Assistance Programme (Indonesia - The Netherlands) 1974-1977. Lembaga Penelitian Tanah, Bogor, Indonesia: 74-92. Suoninen, A. 1976. New ideas and technologies in utilization of peatlands and peat in industry. Proceedings of the 5th International Peat Congress, Poznan. Supardi. 1983. Kegunaan Gambut dan Perkembangannya do Indonesia A.L. Penyelidikan di Rasau Jaya. Sub. Dit. Eksplorasi Batubara, Dir. Sumber Daya Mineral. Suszcynski, E. 1984. The peat resources of Brazil. Proceedings of the 7th International Peat Congress, Dublin 1:468-492. Tate, R.L. 1980. Environmental factors limiting microbial activity in Histosols. Proceedings of the 6th International Peat Congress, Duluth: 695-699. Tate, R.L. and Mills, A.L. 1983. Cropping and the diversity and function of bacteria in Pahokee muck. Soil Biology and Biochemistry 15:175-179. Tate, R.L. and Terry, R.E. 1982. Nitrite production in Pahokee muck: frequency of occurrence and source. Soil Science 133, (4): 213-217. Tay, T.H. 1969. The distribution, characteristics, uses and potential of peat in West Malaysia. Journal of Tropical Geography 29:58-63. Terry, R.E., Tate, R.L. and Duxbury, J.M. 1981. The effect of flooding on nitrous oxide emissions from an organic soil. Soil Science 132, (3): 228-232. Terry, R.E., Tate, R.L. and Duxbury, J.M. 1981. Nitrous oxide emissions from drained, cultivated organic soils of South Florida. Journal of Air Pollution Control Association 31. 171

Thomas, F.H. 1962. The effect of depth to water table on growth and chemical composition of oat forage and field corn. Proceedings of the Florida Soil and Crop Science Society 22:73-78. Tie, Y.L. and Kueh, H.S. 1979. A review of lowland organic soils of Sarawak. Department of Agriculture, Technical Paper 4, Research Branch, Sarawak, Malaysia. Toth, A. 1980. Utilization of peatland for purification and emplacement of communal sewage-mud. Proceedings of the 6th International Peat Congress, Duluth: 711-712. Unger, J.L. 1963. De klink van veengronden. Nederlandsche Heidemaatschappij, Internal paper. Unger, J.L. 1981. Winning en gebruik van turf als Brandstof. Internal Document. Unger, J.L. 1982. Land selection and planning for Peat Mining. Seminar on peat for energy use Euroconsult paper, Bandung, Indonesia. USAID. 1980. Environmental assessment of Burundi peat project. Mission Report Peat II (6950103). Volarovich, M.P. and Churaev, N.V. 1968. Application of the methods of physics and physical chemistry to the study of peat. Transactions of the 2nd International Peat Congress, Leningrad (Ed. R.A. Robertson) 2:819-831. HMSO, Edinburgh. Volk, B.G. 1973. Everglades Histosol subsidence: 1. CO 2 evolution as affected by soil type, temperature and moisture. Proceedings of the Florida Soil and Crop Science Society 32:132-135. Von Post, L. 1924. Das genetische System der organogenen Bildungen Schwedens. Memoires sur la nomenclature et la classification des sols. International Committee of Soil Science, Helsinki: 287-304. Voorde, van der, P.K.J. 1962. Soil conditions of the Isla Macareo, Orinoco Delta, Venezuela. Boor en Spade 12:6-26. Voort, van der, M. 1942. Veen en Veencultuur in de Anaivlakte op Sumatra’s westkust. Landbouw 18:189-202. Waksman, S.A. 1942. The peats of New Jersey and their utilization. New Jersey State Department of Conservation. Geological Series Bulletin No. 55. Waksman, S.A. and Purvis, E.R. 1932. The microbiological population of peat. Soil Science 34:95113. Waksman, S.A. and Stevens, K.R. 1929. Contribution to the chemical composition of peat: V. The role of micro-organisms in peat formation and decomposition. Soil Science 28:315-340. Weir, W.W. 1937. Subsidence of peat land in the Sacramento San Joaquin delta of California. Transactions of the 6th Commission International Society of Soil Science, Zurich: 304-314. Wille, D. 1984. Utilization of peat in horticulture. Proceedings of the 7th International Peat Congress, Dublin 4:466-170.

172

Wilson, N.E. 1972. Cell structure of organic soils under shearing stresses. Proceedings of the 4th International Peat Congress, Espoo. Winkler, M.G. and DeWitt, C.B. 1985. Environmental impacts of peat mining in the United States: Documentation for Wetland Conservation. Environmental Conservation 12:317-330. Zhu Zhipei, Yuan Junlu, Wang Zenghui, Chen Piya. 1984. A preliminary study of the removal of Pb, Cd, Zn, Ni and Cr cations from wastewaters with several Chinese peats. Proceedings of the 7th International Peat Congress, Dublin 3:147-152. Zu Wenchen, Ma Xuehui, Wang Rongfen. 1984. The basic properties and utilization of peat in China. Proceedings of the 7th International Peat Congress, Dublin 2:88-100.

APPENDIX 1 - Tests of Organic Soil Materials (source Soil Survey Staff 1975) The following tests of organic soil material can be used in the field or in field offices. Determinations include sodium pyrophosphate extract colour, fibre percentages, and pH in 0.01 M CaCl 2 . Since it is not practicable in the field to base determinations on a dry sample weight, moist soil material is always used. The specific volume of moist soil depends on how it is packed. It is, therefore, important that packing be standardized in order to obtain comparable results by different soil scientists. Materials a. Water; tap water is satisfactory unless so coloured that it affects the pyrophosphate colour test. b. Solid sodium pyrophosphate (Na 4 P 2 O 7 10H 2 O) ground to 2 mm. Air drying makes grinding easier. c. CaCl 2 solution, 0.015 M. d. Sample containers; plastic bags (optional) and 30 cc plastic cups with plastic lids. e. Liquid dispenser; automatic constant volume pipettor, 3 ml capacity, modified to 4 ml by inserting a piece of plastic tubing into the end of the inlet stem. Cap with a rubber bulb from a medicine dropper to reduce leakage in transit. f. Chromatographic paper strips, 0.5 cm by 3 cm or larger. g. pH paper or pH meter. h. Absorbent paper; thick soft chromatographic paper cut into 10 cm squares, or any absorbent colour-fast blotting paper or heavy towelling is satisfactory for a field kit. i. 15, 2.5 and 0.5 ml measures, j. Half-syringe; a 6 ml plastic hypodermic syringe with the body cut longitudinally to make a halfcylinder measuring device. Volume is one-half that indicated on the syringe. k. Sieve, 100 mesh. l. Spatula, 10 cm, plain. Shape the end to conform with the contour of the 2.5 ml measure of halfsyringe. 173

m. Wooden coffee stirrers. n. Marking pencil. o. 10YR and 7.5YR pages of Munsell soil colour book. p. Tweezers. Test Procedure Field samples collected for use in field tests should be representative of the dominant kind of organic material within the layer described and from the same layer on which field estimates of rubbed and unrubbed fibre percentages are determined. The field sample can be collected in plastic bags and the subsample transferred into a cup after thorough mixing, or the mixing can be done at the sample site and only a small subsample placed in a cup for transport to the field office. If protracted storage is likely, the living tissues should be removed before the sample is transferred to a cup because their identifications become progressively more difficult with time. Preparation of sample Place about 25 cc of wetted field sample on a piece of absorbent paper. Smear the soil material over the absorbent paper to mix and bring it in contact with the paper. Or roll the absorbent paper around the sample and remove the water by squeezing with a second piece of absorbent paper. Continue desorption until the soil material no longer glistens but is still very moist. Remove coarse fragments and plant parts that were living at the time of sampling. If not done previously, visually estimate the rubbed and unrubbed fibre percentage. Pyrophosphate colour test Place 1 g of pyrophosphate and 4 ml of water into a 30 ml plastic container. Allow to equilibrate for a few minutes. Pack a half-syringe adjusted to 5 cc mark (2.5 cc volume) level full with moist soil material. In filling, pack firmly with a spatula but avoid expressing water. Transfer soil material cleanly to the container that holds the pyrophosphate solution. Mix thoroughly using a wooden coffee stirrer. Cover and let it stand overnight unless the colour of the liquid changes rapidly and is too dark or has too high a chroma for hemic materials. The temperature should be between 15 and 32°C. Mix again next morning. Insert vertically, by about 1 cm, a strip of chromatographic paper with tweezers. Leave it there until the paper test strip has wetted 2 cm above the slurry surface (about 5 minutes but this may be longer if the cover is closed). Remove the paper test strip with tweezers and tear off and discard the portion to which soil adheres. Place the strip on a piece of blotting paper and press gently with tweezers to make firm contact. Remove the paper strip with tweezers and compare the colour on the side next to the blotting paper with Munsell soil colour charts (Fig. 35). If successive samples are blotted systematically a comparative record is obtained on the sheet of blotting paper.

174

Figure 35. Value and chroma of pyrophosphate solution of fibric and sapric materials

175

Unrubbed fibre percentage (approximate) Adjust a half-syringe to the 5 cc mark (2.5 cc volume) and pack it level full with moist soil. Transfer all the soil material from the syringe to a 100 mesh sieve and wash under a stream of cold tap water run at the rate of 200-300 ml per 5 seconds until the water passing through the sieve appears clean. Wash the residue to one side of the screen and blot from underneath with absorbent tissue to remove excess water. Remove any plant remains that were living at the time of sampling. If a measurable volume is removed, return it to the half-syringe, blot, and record the scale reading (cc) and subtract from the original 5 cc reading. Repack the washed fibres into the half-syringe. Blot further with absorbent tissue. The moisture content should be approximately the same as that of the 2.5 cc subsample previously measured. Record the scale reading (cc) on the repacked syringe. Unrubbed fibre percentage is equal to the reading (cc) times 20 if there is no correction for live tissues. If there is a correction, the percentage equals the reading (cc) divided by the corrected pre-washed volume times 100. Rubbed fibre percentage Transfer the residue from the unrubbed fibre test back to the 100 mesh sieve. Rub the sample between thumb and fingers under a stream of cold tap water running at the rate of 150-200 ml per 5 seconds. Continue until water passing through the sieve appears clean. Clean rubbed fibres will roll between the thumb and fingers rather than slide or smear. Measure the relative volume with the half-syringe and calculate percentage as described in the previous paragraph. pH Place 2.5 cc of the prepared sample in a 30 ml plastic container and add 4 ml of 0.015 M CaCl 2 (gives a final concentration of roughly 0.01 M CaCl 2 with most packed, moist organic materials). Mix, cover, and allow to equilibrate at least 1 hour. Uncover and measure its pH with either pH paper or a meter.

APPENDIX 2 - Volumetric Relations in Soil Materials (Source Skaven-Haug 1972) Solid matter The solids in soil materials range from organic substances in pure plant material to mineral matter in pure sands, clays or silts. At the same time the specific gravity of the solids, D s , varies from D o in pure plant material to D m in mineral matter. For the majority of soil materials, containing both organic and mineral matter in the solids, the numerical value of D s is an expression of the ratio organic matter/mineral matter. The specific gravity D o for pure organic matter is not constant. It varies with habitat, species present and degree of decomposition. The principal constituents, cellulose and lignin, have specific gravities of 1.52 and 1.46 t/m3 respectively. Literature on the subject gives a specific gravity of 1.53 for fresh spruce and pine while values for other materials lie between 1.47 and 1.52. As a practical estimate D o = 1.50 t/m3 Also the specific gravity D m for pure mineral matter is not constant. It can vary from 2.3 t/m3 for gypsum to 5.2 t/m3 for hematite for example. In mineral soils a large number of minerals are present, and the mean specific gravity varies between much narrower limits. A collection of data from many soil mechanics laboratories shows a variation between 2.65 and 2.85, and generally speaking the lower value is found in coarse and uniform sand, with values rising the more finely divided the material becomes. For Norwegian sand and clay sediments the specific gravity lies between the following limits which for practical purposes we also choose: D m = 2.7 t/m3 ± 2% for sand D m = 2.8 t/m3 ± 3% for clay 176

The dry specific gravity D d is the weight of solids per unit of volume, t/m3 For groups of materials with approximately constant specific gravity for their solids, D d is a serviceable expression for both weight and volume ratios. This measure is used in international soil mechanics as a characteristic of the quantity of mineral matter. The Norwegian Bog Association has for many years used the corresponding measure g/dm3 in dry peat in its investigations of bogs and D d can be regarded as a suitable measure of solidity compaction in peat and bark material. For the large group of soil materials with varying specific gravity of solids D s , D d is not suitable as a basis for comparison. Water The amount of water that the soil material contains, or in certain circumstances can contain, depends on the physical properties of the material. The water content is therefore used as a basis of comparison of soil parameters and as an expression of their quality. The water content may be expressed as the ratios: weight of water/weight of dry matter (w) weight of water/total weight (w tot ) volume of water/total volume (w v ) All three ratios are in use, and this has sometimes caused confusion. As explained above the weight expressions are not always reliable as a basis for comparison. The weight ratio w has been adopted in international soil mechanics and is in general use in technology. For groups of materials with approximately the same D s , w is a serviceable basis of comparison. For materials with variable D s , w is not a good parameter for reference. This can be illustrated by an extreme example. A cubic metre of saturated Norwegian clay contains 0.5 m3 of water, and has w = 0.36 = 36 percent. Peat (agricultural peat in bales) with the same water content, 0.5 m3, has w = 5.0 = 500 percent. The weight ratio w tot been used for a long time in peat terminology, and for peat with approximately the same weight of dry matter it gives a serviceable basis for comparison. One advantage is that w tot is always less than 100 percent. The volume ratio w v is determined by weighing a known volume, before and after drying. Volume determinations cause extra work, but they make it possible to determine both w v and D d . When D s is known, the weight and volume relationships can be calculated in the 3-phase system of water, solids and air. Some technical calculations need quantities of water and thus of w v . Artificial drying of materials and the, determination of thermal parameters is an example. Since w v is also a good basis for comparison, independent of the kind of material, its use should be widely advocated. Air Except for agricultural literature the air content of soil is rarely used. This is probably because of its insignificant weight, so that it must be stated as a volume. The air content of soil is often directly indicative of certain properties, such as low specific gravity, low thermal conductivity, and a large capacity for absorbing water. Formulae Weight and volume ratios can be derived from the unit volume (Fig. 36). Here is a survey of

177

formulae that are suitable for practical use: Symbols w w tot wv D Dd Ds sv n sr Do Dm ov mv lv o m a

ratio of weight of water/dry matter ratio of weight of water/total weight ratio of volume of water/total volume bulk density of wet material specific weight of dry material (dry density) specific gravity of solids ratio of volume solids/total volume porosity degree of saturation specific gravity of organic matter specific gravity of mineral matter ratio of volume of organic matter/total volume ratio of volume of mineral matter/total volume ratio of volume of air/total volume ratio of weight of organic matter/dry matter ratio of weight of mineral matter/dry matter ratio of weight of ash/dry matter

For practical purposes the weight of air is regarded as zero, and the specific gravity of water as unity. The numerical values of the volume and weight of water are thus equal, and the factor 1 is omitted from the formulae. Ratios of weight, proportions of volume, porosity and degree of saturation are dimensionless quantities, which if multiplied by 100 give percentages. Specific gravities are reckoned in tons per cubic metre (t/m3). w v = (D x w) ÷ (w + 1) D d = D ÷ (w + 1)

(1) (2)

wv = Dd x w

(3)

Dd = D - wv w v = D x w tot

(4) (5)

D d = D (1 - w tot )

(6)

w v = (D d x w tot ) ÷ (1 - w tot ) sv = Dd ÷ Ds

(7) (8)

l v = (1 - w v ) - s v

(9)

s r = w v ÷ n = (w v x D s ) ÷ (D s - D d )

(10)

178

If the volumes are measured and D s is known, the volume ratios in the 3-phase system, solids, water and air, can be found. If the material is saturated with water we have only two phases, solids and water, and the relations are simpler. Then s v = 1 - w v If the volumes are measured, D s can be calculated. We shall come back to this later. The relation between w tot and w v , equation (7), is shown in Figure 36 for a number of organic materials with D s = 1.55 t/m3 and known values for D d . The highest two curves are related to slightly decomposed sphagnum peat in bogs. The curve for which D d = 0.10 t/m3 corresponds to the same peat in agricultural bales for protection against frost under railway tracks. The bottom curve, with D d = 0.25 t/m3 relates to bales of bark under roads and railways. For bark matting in situ with measured w tot = 0.72, we may read off, in round figures, w v = 0.65, l v = 0.19 and s v = 0.16. Fig. 36. Relationship of weight and volume ratios for a range of organic materials with known specific gravities

179

Fig. 37. Cubic unit of a soil material with four phases: organic substance, mineral substance, water and air

Proportions of organic and mineral substances The dry material may contain both organic and mineral matter, and D s is then the mean specific gravity. It remains to determine the quantitative relations between organic and mineral substances. By considering Figure 37 and setting up weight and volume equations we get: o v = D d (D m - D s ) ÷ D s (D m - D o )

(11)

ov + mv = sv m v = D d (D s - D o ) ÷ D s (D m - D o )

(12)

In the same way we have the following mutual relations for weight: o = D o (D m - D s ) ÷ D s (D m - D o )

(13)

o+v=1 m = D m (D s - D o ) ÷ D s (D m - D o )

(14)

We now have a complete survey of the volume and weight relations in the 4-phase system, organic matter, mineral matter, water and air. We can easily measure D d and D o , and D m may be regarded as known. It remains to determine the key value D s . The Specific Gravity of Solid Matter There are several methods of determining D s . a. The pycnometer method can in principle be used for all soil materials, but is time-consuming, especially when it comes to removing the last vestiges of air in organic matter, and is not suitable for routine investigations.

180

b. For cohesive soils saturated with water, e.g. silt, clay and mud, commensurable volumes can easily be prepared and D s can be calculated. The measurement of volume can also be carried out by weighing in air and when submerged in water. This method is suitable for routine investigations, but is limited to the above mentioned saturated materials. c. The weight ratio can be found by chemical means, and then D s calculated from formula (13). A distinction is made between direct and indirect methods. The direct methods consist of removing the organic matter and weighing what is left. The best method is by ignition, which will be described later. Indirect methods are based on the assumption that a particular element is contained in the organic substance in a constant proportion, so that the organic substance can be calculated for this element by means of a conversion factor. These methods, like the direct ones, are not fully accurate, but must be regarded as the most reliable for soil materials with only moderate contents of organic matter.

APPENDIX 3 - Soil and Other Physical Limits for Satisfactory Crop Growth on Organic Soils (source Maas et at. 1979) APPENDIX 3. Soil and Other Physical Limits for Satisfactory Crop Growth on Organic Soils 1

The clay content of the mineral component must be 18 percent (Soil Survey Staff 1975).

2

n.r. - no restriction

3

Forage crops - although pasture grasses can be grown under the conditions stipulated, the trafficability of animals is uncertain. It is noted that lighter animals like goats may not pose a problem and that the trafficability is probably better where the mineral content is higher. 4

Frequent, but short-term flooding acceptable for clove, nutmeg and rambutan; infrequent, long lasting floods for citrus, durian, guava and mango.

APPENDIX 4 - Linking Drainage and Soil Temperature (source Stephens et al. 1984) In developing a mathematical model linking drainage depth and soil temperature that could be used to estimate subsidence of low moor peats in different climates, Stephens and Stewart (1976) applied the Arrhenius Law to both water-table and laboratory findings. (Arrhenius showed that the logarithm of the velocity coefficient, k, of a chemical reaction is linearly related to the reciprocal of the absolute temperature, T.) Stephens et al. (1984) then developed the “Stephens-Stewart-Chew” basic subsidence equation, which follows: S T = (a+bD) ek(T-To) (1)

181

where ST = biochemical subsidence rate at temperature, T, D = depth of water-table, e = base of the natural logarithm, k = reaction rate constant, To = threshold soil temperature where biochemical action becomes perceptible, a and b are constants.

Using the empirical relationship where S T multiplies to Q 10 x S (T + 10) where Q 10 is the change in reaction rate for each 10°C rise in temperature, then S (T+10) = Q 10 x S T = (a+bD)ek[(T+10)-To] (2)

Dividing equation (2) by equation (1): S (T+10) ÷ S T = Q 10 = e10k (3)

By rewriting (2) to express k in terms of Q 10 k = 1 ÷ 10 in Q 10 (4)

and substituting (4) into (1), S T = (a+bD)Q 10 [(T-To) ÷ 10] (5)

From laboratory studies, the value of Q 10 was assumed to be 2.0 and the value of T o to be 5°C. The relationship found between drainage depth, soil temperature, and annual subsidence rates on the water-table plots at the Everglades Experiment Station was chosen to find the value of constants a and b where the measured annual soil temperature was 25°C. Thus, from Figure 20 p. 87, when D = 40 cm, S = 2.29 cm per year, and D = 80 cm, S = 5.00 cm per year. Substituting these values into (5) and solving the simultaneous equation to evaluate a and b, we find that a = 0.1035 and b = 0.0169. Then from (5) S x = [-0.1035 + (0.0169 x D)] x 2[(Tx-5) - 10] (6)

Stephens and Stewart (1976) recommend that equation (6) be used to estimate the biochemical subsidence rate for low moor organic soils at locations where the annual average soil temperature at 10 cm depth is T x . For example, equation (6) is used as follows to estimate the annual subsidence rate, exclusive of compaction or other bulk density change, at the Lullymore Experimental Station in the Irish Republic for arable low moor soils where the average annual soil temperature is 8.5°C and the water-table depth is held at 90 cm: S L = [-0.1035+(0.0169 x 90)] x 2[(8.5-5.0) ÷ 10] S L = 1.4175 x 20.35 (7) S L = 1.4175 x 1.27 = 1.80 cm per year

182

This indicates that if the Everglades Histosols were transposed to Lullymore, the rate of decomposition would be only 32 percent of the rate in southern Florida where T = 25°C. If the Everglades soils were in a more tropical climate where the average soil temperature was 30°C, for example, again from (6) S x = [-0.1035 + (0.0169 x 90)] x 2[(30-5) ÷ 10] (8) S x = 8.02 cm per year

Which is 43 percent greater than the decomposition rate for southern Florida. For convenience in estimating S x for any selected temperature, T x , the results from equation (6) were plotted at water-table depths, D, of 30, 60, 90 and 120 cm, which has been reproduced as Figure 20. Stephens and Stewart (1976) cite the shortage of field and laboratory data as a limitation of the mathematical model, but also point out that if future studies indicate that the values of Q 10 and To should be adjusted the mathematical procedure for computations is still valid. Only the constants for a and b would change. For instance, where Q 10 = 1.5 and T o = 0°C, then a = -0.1523, and b = 0.0246. When using equation (6) or the graph, Figure 21, remember these values were developed from organic soils with a mineral content of less than 15 percent and a bulk density of approximately 0.22 g/cm3 In muck soils with a greater mineral content and higher bulk density, the expected subsidence rates, depending on the increase in mineral content, will be between one-half and three-quarters of those shown by Figure 21 or equation (b). Calculation of the Surface Compression of a Bog (Source Murashko 1969) The process of surface compression of a bog with time may be described by the following differential equation: -dH ÷ dt = KhH (1)

where: -dH ÷ dt H h t K

the speed of compression in metres per year (the negative sign shows that compression decreases with time), the depth of the bog, in metres, the depth of drains, in metres, the duration of drainage, in years, “the constant” of compression, the quotient which depends on the physical properties of peat, in metres per year.

183

The formula for calculating surface compression of low-lying bogs at the borders of open canals and near drains, which results from integration of equation (1) and utilization of experimental data, has the form: S n = AH o {l-exp[-h(a+bt)]} (2)

where: A is the quotient of peat density, which depends on the volume weight of the solid matter; Ho is the thickness of peat before draining, in metres; a and b experimental quotients (a = 0.07m-1;b = 0.06m-1, year-1).

For practical calculation using equation (2), it is necessary to know the thickness of the peat layer before draining and the volume weight of solid matter, and to define the drain depth sufficient for successful agricultural production or other purposes. In designing draining systems, the value of t in equation (2) should be for the drainage operation of the project, or the time for repairing or reshaping the drainage system. For bogs where wooden drains are installed, and the operation time is between 15 and 20 years, the compression should be calculated taking into account half of this term and assuming that the mean depth of the groundwater will be slightly higher for the first half of the operation period and slightly lower than the optimum depth for the second half. For ceramic drains, with operation terms of 40-50 years, the calculation value of the compression should be defined for t = 20-25 years. For a drainage system, t is assumed to be equal to the time after which repairs or reconstruction of the drainage system is planned, that is approximately for 5 to 10 years. Equation (2) is correct when t³1 and the constant depth of water in drains is h o = 5-40 cm. If the designed depth of water in the canal is assumed to be more than the above mentioned value, the canal depth h be reduced by the value of the excess. For example, if h = 2.5m and h o = 1.0m, then the value of h = 2.5 - (1.0 - 0.4) or 1.9 m, which should be used in equation (2). This assumption is based on the fact that when the water-table of the bog is constantly near the canal borders the compression of peat will not take place. Values of the quotient of peat density. A, are defined by the value of volume weight of solid matter according to the monogram (Fig. 38). The magnitude of the volume weight of dry peat should be defined by selection of samples with intact structure taken through the whole depth of the peat bog. In case the peat layer is inhomogeneous, such as when there are different layers with thickness of l 1 , l 2 ,..., l n with different density through the depth of the bog, then the volume weight of the solid matter should be defined as a “mean weighted value”. d = (d 1 l 1 + d 2 l 2 + ... + d n l n ) - (l 1 - l 2 + ... + l n ) (3)

184

Figure 38. Momogram for choosing peat bog density quotient A

Since it is difficult to define the weight of solid matter of an undrained layer under production conditions, it is possible to choose values of A by means of the value of natural humidity, W, and the degree of decomposition, R. Determination of W and R is made by selecting samples with disturbed structure through the whole peat thickness. The nomogram (Fig. 38) also shows the method of defining the quotient A by these factors.

185

FAO SOILS BULLETINS 1. Soils of the arid zones of Chile, 1966 (E**) 2. Survey of soil laboratory in 64 FAO member countries, 1965 (E**) 3. Guide on general specialized equipment for soil laboratories, 1966 (E**) 4. Guide to 60 soil water conservation practices, 1966 (E**) 5. Selection of soil for cocoa, 1966 (C* E** F** S**) 6. Aerial photo interpretation in soil survey, 1967 (E* F* S**) 7. A practical manual of soil microbiology laboratory methods, 1967 (E**) 8. Soil survey interpretation and its use, 1967 (E**) 9. The preparation of soil survey reports, 1970 (E** F** S**) 10. Physical and chemical methods of soil and water analysis, 1970 (E* F* S*) 11. Soil fertility investigations on farmers’ fields, 1970 (E* F* S*) 12. A study on the response of wheat to fertilizers, 1971 (E*) 13. Land degradation, 1971 (C* E*) 14. Improving soil fertility in Africa, 1971 (E** F**) 15. Legislative principles of soil conservation, 1971 (E*) 16. Effects of intensive fertilizer use on the human environment, 1972 (E*) 17. Trace elements in soils and agriculture, 1972 (E* F* S*) 18. Guide to the calibration of soil tests for fertilizer recommendations, 1973 (E* F* S**) 19. Soil survey interpretation for engineering purposes, 1973 (E* F** S**) 20. Fertilizer legislation, 1973 (E** S*) 21. Calcareous soils, 1973 (E* F*) 22. Approaches to land classification, 1974 (E**) 23. Management properties of ferralsols, 1974 (E*) 24. Shifting cultivation and soils conservation in Africa, 1974 (E* F* S*) 25. Sandy soils, 1975 (E*) 26. Planning and organization of fertilizer development in Africa, 1975 (E**) 27. Organic materials as fertilizers, 1975 (E* F** S**) 28. S.I. units and nomenclature in soil science, 1975 (E*) 29. Land evaluation in Europe, 1976 (E**) 30. Soil conservation in developing countries, 1976 (E* F* S**) 31. Prognosis of salinity and alkalinity, 1976 (E*) 32. A framework for land evaluation, 1976 (C* E* F* S*) 33. Soil conservation and management in developing countries, 1977 (E* F*) 34. Assessing soil degradation, 1977 (C* E*) 35. Organic materials and soil productivity, 1978 (C* E*) 36. Organic recycling in Asia, 1978 (C* E**) 37. Improved use of plant nutrients, 1978 (C* E*) 38/1. Soil and plant testing and analysis, 1980 (E*) 38/2. Soil and plant testing as a basis of fertilizer recommendations, 1980 (E** S*) 39. Salt-affected soils and their management, 1988 (E*) 40. China: recycling of organic wastes in agriculture, 1978 (E* F* S*) 41. China: azolla propagation and small-scale biogas technology, 1979 (E* F* S*) 42. Soil survey investigations for irrigation, 1979 (C* E*) 43. Organic recycling in Africa, 1980 (E*) 186

44. Watershed development with special reference to soil and water conservation, 1979 (C* E* F* S*) 45. Organic materials and soil productivity in the Near East, 1982 (E*) 46. Blue-green algae for rice production - a manual for its promotion, 1981 (E*) 47. Le recyclage des résidus agricoles organiques en Afrique, 1982 (F*) 48. Micronutrients and the nutrient status of soils: a global study, 1982 (E*) 49. Application of nitrogen-fixing systems in soil management, 1982 (E* F* S*) 50. Keeping the land alive: soil erosion - its causes and cures, 1983 (E* F* S*) 51. El reciclaje de materias orgánicas en la agricultura de América Latina, 1983 (S*) 52. Guidelines: land evaluation for rainfed agriculture, 1983 (E* F*** S*) 53. Improved production systems as an alternative to shifting cultivation, 1984 (E* F* S*) 54. Tillage systems for soil and water conservation, 1984 (E* F*** S***) 55. Guidelines: land evaluation for irrigated agriculture, 1985 (E* F*** S***) 56. Soil management: compost production in tropical and subtropical environments, 1987 (E* F***) 57. Soil and water conservation in semi-arid areas, 1987 (E* F***) 58. Guidelines: land evaluation for extensive grazing, 1988 (E*) 59. Nature and management of tropical peat soils, 1988 (E*)

Availability: April 1988 C - Chinese * Available E - English ** Out of print F - French *** In preparation S - Spanish

The FAO Soils Bulletins can be purchased locally through FAO sales agents or directly from Distribution and Sales Section, FAO, Via delle Terme di Caracalla, 00100 Rome, Italy. http://www.fao.org/docrep/x5872e/x5872e00.htm#Contents

187