Water Requirement of Different Crops Booklet No. 226 Irrigation: IRS - 11 Contents Preface I. Introduction II. Soil, Plant and Water III. Use of Water by Plants IV. Water Requirement of Crops V. Guidelines to Efficient Use of Water VI. Irrigation Requirement of Different Crops VII. Water Use Efficiency Preface Water is an important component for plant growth. It constitutes three-fourth of the body weight. The water is either supplied by rain or irrigation. An efficient utilization of irrigation is essen essentia tiall to supply supply water water at the the differ differen entt criti critica call stag stages es during during plant plant growt growth h to deter deter the the economic loss. Though water is an economic input, it differs from other inputs in many respects. Suppose water is produced like fertilizers or chemicals, its cost would be enormous. Therefore, maximum yield per unit water applied should be more. This booklet describes the most efficient use of irrigation in detail. Dr. K. T. Chandy, Agricultural & Environmental Education I. Introduction Climate, soil and water are the three basic resources which determine the nature of crops that can be grown successfully in a particular region. An efficient utilization of these resources is essential for optimum production of food and fibre for human life, feed for cattle and raw materials for industry. Climate determines the suitability of a region as a habitat for different flora and fauna, also the availability of water for production of Crops and other uses. Under a given set of environmental environmental conditions production of crops is limited by the availability availability of nutrients and water. water. Soil provides provides anchora anchorage ge for the plants and serves as a reservoir reservoir of water water and nutrient required by them. Chemical fertilizer can supplement nutrients to poor soil, but there is no subs substit titute ute of water water for for produc productio tion n of crops crops.. As the the resou resource rces s are are limite limited d an effici efficien entt managem management ent is of utmost utmost importan importance ce for sustain sustaining ing and increasi increasing ng agricult agricultural ural producti production. on. Competing demands of water for domestic use, sanitation, industrial and recreational purposes makes it more essential to maximize the efficiency of water for agricultural production. production. Agriculture consumes the largest amount of available available water, yet, it uses water less efficiently. If food crisis is to be solved, there is no other alternative than to increase area under irrigation which can be made possible only when we use our present water resources most judiciously for irrigating irrigating our our agricultural crops. crops. II. Soil, Plant and Water Soil acts as a reservoir of water for the plants to use through root zone system. When rainf rainfal alll is inad inadequ equat ate e or untim untimely ely,, appli applica catio tion n of irriga irrigatio tion n water water becom becomes es essent essential ial for for successful growth of crops.
The factors influencing plant growth and productivity may be grouped as follows. A. Soil factors The major major soil factors factors are: soil moisture, moisture, texture, texture, structure structure,, density density,, salinity salinity,, fertility fertility,, aeration, temperature and drainage. B. Plant factors The major plant factors are: types of crops, density and depth of rooting, rate of root growth, aerodynamic roughness of the crop, drought tolerance and varietal effects. C. Climate factors The climatic factors are: sunshine, temperature, humidity, wind and rainfall. D. Miscellaneous factors Some of the major miscellaneous factors are: soil volume, plant spacing, crop and soil management. Water is retained around the soil particles and in capillary pores by the forces arising out of surface tension and presence of salts. A plant has to overcome retentive forces to absorb water ; from the soil. The upper limit of water retention is limited to the field capacity of the soil. Any amount of water added to soil in excess of field capacity is not going to be retained in the root zone of the crop. When the soil texture is more of the clay content, the field capacity value increases. Time required for draining of the excess water also depends on soil texture. When the amount of water is reduced to a permanent wilting point, at this point or below plants can no longer absorb water and survive. The moisture content between field capacity and permanent wilting wilting point point is known as available available soil moisture moisture regime regime for plant plant growth. growth. Humid Humid conditions conditions enables plants to draw soil moisture almost up to the permanent wilting point. On the other hand in hot and dry conditions, plants may show wilting symptoms in spite of enough available water present in the root zone. Plants use only about 5% of the total water absorbed for physiological functioning. Most of the water is lost in transpiration and, therefore, it has to be replaced. Water absorption, conduction, translocation and water loss through transpiration are some of the main processes in plant growth. Water absorption by roots is dependent on the supply of water at the root surface and growth of roots in the soil mass. As the soil dries from saturated state, the rate of water movement in the soil decreases rapidly. The root system must expand continuously to provide the plant with sufficient water to replace the transpiration transpiration losses through the leaves. The internal water balance in a plant depends on the relative rates of water absorption and loss. Water stress whether mild, moderate or severe can affect photosynthesis, respiration, growth and reproduction of plant. Water stress at certain critical stages causes more injury to plant growth and productivity. Some plants survive water stress owing to their drought resistant qualities. Since field capacity and wilting percentage are peculiar to soils, water absorption may be effectively controlled by adopting an effective root zone. Shallow rooted plants like paddy and potato require frequent water application than moderately deep and very deep rooted crops such as wheat, groundnut, maize, sorghum, cotton and sugarcane. Moisture is extracted to a larger extent from the first quarter of the root zone than others.
Trans Transpir pirat ation ion is the the proces process s by which which water water vapou vapourr from from plant plant leaves leaves enters enters the the atmosphere. Though it is essentially a process of evaporation, it is different from the latter in several aspects. Evaporation from leaves meets with considerable amount of resistance like an open surface. Evapo-transpiration (En is the quantity of water transpired by the plants during their growth, or retained in the plant tissues, plus the moisture evaporated from the surface of the soil and vegetation, i.e. the amount of water between field capacity and wilting point within the root zone become available for ET. This is nothing but the consumptive use (CU) of water by the plants, because water used for metabolic activities is very insignificant (less than 1 % of En and, therefore, it denotes use for losses due to ET. Under field conditions, solar radiation supplies the energy for ET process. Wind is also important in removing water vapour from the field. III. Use of Water by Plants The kind and the extent of various plant roots largely determine the amount of water required at each irrigation. Roots usually; represent one half or even more of the total weight of the plants. Water is absorbed mainly through root hairs of the roots near the terminal portion. Root hairs are usually very minute and they can not be seen by naked eye. Several hundred of root hairs may be located on a square millimeter of the root surface. With rapid root growth larger number of root hairs are sent into small soil capillaries and crevices between soil particles contacting and absorbing soil water. After absorption absorption by the roots, the water moves up the stem of the plant and into the leaves where it is given off as vapour. This loss of water is controlled to a limited extent by openings (stomata) in the leaves. The stomata are capable of opening and closing. There is very close relation relationship ship in the opening opening of stomata stomata,, transpira transpiration tion rate and the soil soil moisture moisture condition. IV. Water Requirement of Crops The Water Requirement (WR) of crops depends upon retention and transmissivity of water in soil, absorption and transmission within plant, transpiration, effective rainfall, vapour pressure, and energy. WR is that quantity of water regardless of its sources required by a crop in a given period of time for its maturity. It includes losses due to ET or CU plus the losses during the application of irrigation water which may be unavoidable. Irrigation requirement (IR) of a farm is the sum total of irrigation need for an individual crop crop in a specif specified ied time time plus plus the losse losses s occurr occurring ing in field field distr distribu ibutio tion n such such as seepag seepage, e, percolation etc. Similarly, IR for a command area will constitute the sum of water needs for individual farms plus the loss taking place in the distribution system in that area. Net irrigation requirement (NIR) is the depth of irrigation water, exclusive of precipitation, carry-over soil moisture or ground water contribution which is required for plant growth. It is that amount of irrigation water which is required to bring the soil moisture of the effective root zone to field capacity (PC). Thus, it is the difference between FC and soil moisture content in the root zone before irrigation. irrigation. Irrigation frequency depends on CU of a crop and the amount of available moisture in root zone. Sandy soils must be irrigated more often than fine textured deep soils. In general,
irrigation should be given when, about 50 to 60% of the available soil moisture has been used from the root zone. The critical periods during the stages of growth are very important factor. Irrigation period is the number of days that can be allowed for applying one irrigation to a given area during the peak CU period. The aim of the irrigation schedule should be to obtain maximum yield per unit area. In case of water resources being defined the objective should be to obtain maximum production per unit of water. In heavy soils, depletion of available moisture is at a slower rate and in a lighter soil it is at faster rate. For paddy, it is enough to impound 5 cm of water and recharge to the same level once in four days or when the field comes to a saturation point but before the formation of hairline cracks, whichever is earlier. For maize at 25% depletion of water, irrigation frequency should be once in four days and six days in case of clay soils. Cotton and groundnut groundnut requires irrigation once in 10 days in red and 15 days in clay soils when the depletion of available available soil moisture is 75 per cent. Other soils which fall in between red and clay loams, may have to be irrigated once in 10 or 15 days at the level of depletion. V. Guidelines to Efficient Use of Water The following are some guidelines for improving irrigation practices and efficiencies for different field crops. 1. Before irrigating, check the soil moisture in the root zone at several locations and estimate the amount of water require to bring the soil to field capacity. About 2 -3 days after an irrigation, check the soil moisture again. The moisture should be close to field capacity throughout the rooting depth. There should be no dry spots or dry l ayers in the field. 2. Determine the depth of water in centimeters applied to the field during irrigation. For this, the measurement of the stream size and the period of time for which water was delivered to the field are required. Then calculate the depth applied. For sprinkler irrigation multiply the application rate in millimeters per hour by the length of time in hours. 3. How does the estimation of the amount of water needed compare with the amount delivered to the field? About what efficiency irrigation was obtained? Note that high efficiency can be secured, but a poor irrigation may result if only a small amount of water is applied on the dry soil. 4. During irrigation, see whether the intake opportunity time is about the same throughout the field. When irrigation is done by the border method, does the water-stand about as long at the lower and middle of the field as it does at the upper end? If furrows are used, does the water reach the lower end at I about one fourth of the total time that it is on the upper end? Are basins and level borders filled quickly? 5. Observe the amount of irrigation water flowing out of the field as waste. A large amount of surface water flowing out from a border indicates that the stream is too large or water has been running running into the border border strip for a long time. When the water in a well designe designed d border border (not a level border) approaches the lower end of the strip, the stream may be reduced or cut off at the upper end. In this way, an even distribution will be obtained with little or no run-off. The stream size must be properly adjusted to the soil intake rate and to the border length if the border is to be evenly irrigated without excessive run-off. If furrow run-off is excessive, the furrow stream should be reduced to about one-third to two- thirds of the initial flow after the water reaches the lower end.
VI. Irrigation Requirement of Crops Several experiments on various crops for their irrigation requirements have highlighted the following results. A. Paddy Paddy is a semi-aquatic plant and covers about 35% of irrigated area in the country. Different varieties have been evolved to suit different regions, season and water availability. Cultural practices like puddling and transplanting reduce percolation losses, weed growth but increase the availability of plant nutrients and regulate soil and water temperatures. It improves photo photosy synt nthes hesis is in the lower lower leaves leaves due due to reflec reflected ted light light from from the the water water surfa surface. ce. These These operations may require about 200 -300 mm of water per hectare. Submergence below 50 mm for low land rice has been found to yield low. Recent researches have shown that continuous submergence submergence throughout the growth period may not maximize the yield. Selective submergence during during critic critical al stag stages es (initi (initial al tiller tillering ing,, pani panicle cle initia initiatio tion n to flowe flowerin ring) g) would would be suffic sufficien ientt to maximize yield and to save water during the monsoon period. However, However, during during summer, summer, continu continuous ous submerg submergence ence has to be followe followed d for maximum maximum yields, Proper drainage drainage helps to remove the toxic substances and regulate the oxygen supply to the roots. About 15 to 20 days prior to harvest, irrigations are stopped and water is drained to facilitate harvesting operations. A major problem in paddy irrigation is deep percolation losses which which is 50 to 75% 75% of water water appli applied. ed. Reduc Reductio tion n of deep deep perco percolat lation ion of water water is gener general ally ly achieved achieved by soil manipulati manipulation on of three types types viz. viz. (i) Puddling Puddling (ii) compaction compaction,, and (iii) subsubsurface surface placemen placementt of impermea impermeable ble material materials s like bitumin and plastic plastic films. films. Because Because of its prohibitive cost and mechanical difficulty, the third option is not practicable at farmers field. Farmers generally continue to irrigate rice till about 4 -7 days before harvest. A recent study has stated that suspension of last irrigation for 14 -17 days before harvest causes more uniform ripening of the crop and economises 16 cm of irrigation water. However, termination of irrigation 3 weeks before harvest may cause marginal yield decrease, but it will save about 20 cm of irrigation water. The critical stages for irrigation in rice crop are tillering, panicle initiation, flowering and grain filling stage. The irrigation requirement of paddy at different locations are given in table 1. Table 1: Water and irrigation requirement or rice at different locations Sl.No.
Place
1
Kharagpur (WB)
2
Cuttack (Orissa)
3
Bhubaneshwar (Orissa) Roorkee (U.P) Dhanauri (U.P.) Karnataka Hyderabad (A.P)
4 5 6 7
Water requirement (Mm) 1890 2150 1300 1190 1440 1650 1620 1630 1520 N.A.
Irrigation Requirement (mm) 1440 N.A 790 780 780 1630 750 910 1170 780
Seasons
July/Aug/-Nov/Dec. Dec/Jan – Mar/April June-September Jan- April June-September Sept-Dec June-October June-October June-October Mar-June
8
Coimbatore
N.A
1680
9 10 11
Chalakudy (Kerala) Delhi Ludhiana
N.A 2400 N.A.
1520 1600 1240
N.A. July/Aug Dec/January Feb-May June-October June-October
B. Wheat Wheat is the second most important crop of the country and the area under this crop has been on the increase during the last two decades. It is grown during winter and about 59% of its area is irrigated irrigated.. Recently Recently introduc introduced ed dwarf dwarf varietie varieties s are highly highly respons responsive ive to irrigation irrigation and fertilization. fertilization. The critical stages for
Irrigati Irrigation on are crown crown root root initiati initiation, on, tillering tillering,, jointing jointing,, flowering flowering,, milk stage stage and dough dough stage. The crop develops a deep and dense root system unless restricted by an impeding layer in the profile. Therefore, it can effectively utilize profile-stored moisture, provided post -sowing irrigations are timed to encourage deeper proliferation of roots. The fact is especially important for the major wheat zone of northern India, where at the time of its sowing the root zone profile is either either charg charged ed deepl deeply y with with moist moisture ure from from the the procee proceedin ding g mons monsoon oon or with with pre-so pre-sowin wing g irrigation. Generally, 4-6 irrigations are found to yield in maximum productivity at about 40 to 50% of depletion of available available soil moisture. According to the availability of irrigation water, it may be scheduled as in table 2. Table 2: Number or irrigations according to the availability Sl.No One Two Three Four Five 1 CRI (2 (21 CRI (21 CRI (21 CRI (21 CRI (21 DAS) DAS) DAS) DAS) DAS) Tillering Tillering Tillering (45 DAS) (45 DAS) (45 DAS) 2 Jointing (65 DAS) 3 Boot (75 Boot (75 Boot (75 DAS) DAS) DAS) 4 Flowering (85 DAS) 5 Milk (100 Milk Milk (100 (100 DAS) DAS) C. Sorghum Cult Cultiv ivat atio ion n of sorg sorghu hum m is most mostly ly conf confin ined ed to trop tropic ical al and and subt subtro ropi pica call area areas s in Mabarashtra, Mabarashtra, Madhya Pradesh, Pradesh, Andbra Pradesh, Karnal Gujarat. Rajasthan, Rajasthan, Uttar Pradesh, Tamil Nadu, Punjab and Haryana. Being the third important cereal of the country, the crop is planted in a total area of about 16 million hectares, of which 0.7 million hectares are irrigated. In Punjab, Punjab, Haryana, Uttar Pradesh and some part of Rajasthan, Rajasthan, it is mostly grown for forage rather than grain. The main growing season of the crop extends from March to October. In southern states, it is also taken as a rabi crop during October to February. Exper Experime iments nts have have show shown n that that khari khariff crop crop do not not requir require e any any irrig irrigati ation on,, if there there is sufficient rain during the season. It is a drought resistant crop and can withstand soil moisture depletion up to 75 per cent. Some. varieties of sorghum are of very short duration, adding adding to the
adaptability, adaptability, varied soil and water conditions. Seeding, flowering and sometimes milking are the critical stages when the crop is irrigated in case it is raised as irrigated crop. D. Maize Maize Maize is grown grown both for grain grain and forag forage. e. Maize Maize occup occupies ies an area area of 5.9 5.9 millio million n hectares. It is grown primarily as a kharif crop from March to October in Uttar Pradesh, Bihar, Madhya Pradesh, Punjab, Gujarat, Jammu and Kashmir, Himachal Pradesh, Orissa. Andhra Prad Pradesh esh,, Karn Karnata ataka ka,, Maha Maharas rashtr htra a and and Harya Haryana na.. Some Some also also come come under under rabi rabi crop crop in the the southern, mid west states and more recently in Bihar, Uttar Pradesh and Punjab. Preliminary studies have shown that rabi crop has a higher judicious water management management and is important important for improving the productivity of both kharif and rabi crops. The crop has early vegetative, tasselling and silking stages as critical periods. After dough stage, there is no need of irrigation. The permissible depletion of soil moisture may be 25% in light soils and 50% in sandy loam to loam soils. Some research findings have revealed that crop should not be subjected to excess water- soil submergence during early growth. If the draining out of water in case of heavy rains is delayed, 30 to 60 kg N/ha may be added immediately following drainage drainage to retrieve the yield loss. E. Bajra Bajra is an important millet grown during kharif in warm areas with a seasonal rain of about 15-20 centimeters. It is cultivated on an area of 11.7 million hectares mostly on relatively light textured soils of Rajasthan, Haryana, Punjab, Uttar Pradesh, Kamataka, Gujarat and Tamil Nadu. In most of the areas it is sown with the onset of monsoon and no post-sowing irrigation is appli applied. ed. Howev However, er, the the crop, crop, parti particu cular larly ly the the hybri hybrid d stra strains ins,, has has been been found found to respon respond d to irrigation. Flowering and milking stages are the critical stages of irrigation for bajra crop. The crop gives the optimum yield with irrigation based on 75% depletion of available soil moisture from the top 30 cm layer. Bajra is a drought resistant crop. If there is enough rain, kharif crop does not require irrigation. If there is no rain generally, two irrigations are required, first at flowering stage and second at the milking stage. If moisture is a limiting factor, irrigation should also be done at the time of ear head emergence because it is the most critical stage for moisture stress. Bajra does not tolerate water logging. So, do not allow rain water to remain in the field for more than a few hours. Proper arrangement for draining out of excess water must be made. F. Barley Barley is an important rabi cereal and is also used in brewery industry. It is grown on an area of only 1.75 million hectares in the states of Uttar Pradesh, Madhya Pradesh, Rajasthan, Bihar, Haryana, Punjab and Himachal Pradesh. Its cultivation is preferred to wheat under low fertility, low irrigation and late sown conditions. A few irrigation studies based on growth stages of barley have shown that barley shows favourable response to irrigation particularly if the rainfall is low. Generally, it require two to three irrigations to give good yield. One extra irrigation shal shalll be requir required ed to sand sandy y soils soils.. If suppl supply y of water water is inad inadequ equate ate,, its effici efficien ency cy shoul should d be increased by giving irrigation at critical stages of growth. If only one irrigation is available, it should be given near active tillering stage (30 -35 days after sowing). When two irrigations are available, one should be applied at active tillering and the other at flowering st3ge. On highly saline and sodic soils frequent light irrigation gives better result than few heavy irrigations.
G. Cotton Cotton is cultivated primarily as a kharif crop on an area of 8 million hectares of which only 25% is irrigated. Major cotton growing st3tes are Maharashtra, Maharashtra, Gujarat. Karnataka, Karnataka, Punjab, Madhya Pradesh, Andhra Pradesh, Rajasthan, Haryana and Tamil Nadu. The crop is sown in the hot months of April and May and is harvested during October to November in north-west and mid- west States and December to January in southern states. It requires more frequent irrigation in the southern states where the weather is warm and long season varieties are grown. In the North-west. cotton generally needs 2 to 5 irrigations depending upon the soil type and amount and distribution of seasonal rains. In drier and ill-distributed rainfall conditions, the crop needs 6 to8 irrigations with 50 to 75% soil moisture depletion. Delayed irrigation prevents the plants from making excessive vegetative growth. The first irrigation should be given 40-45 days after sowing and subsequent irrigations should be light and be given at an interval of two to three weeks. The crop should not be allowed to suffer from water stress during flowering and fruiting period, other wise excessive shedding of flower buds and young bolls may occur resulting in the loss of yield. Cotton during its early growth is very sensitive to water st3gnation for long periods. Therefore, proper drainage should be done. H. Sugarcane Sugarcane is an important crop of tropical areas. In India. it is grown on an area of about 3.19 m. ha. in Uttar Pradesh, Karnataka, Haryana. Bihar, Punjab, Gujarat and Madhya Pradesh. It is planted during January to March and is harvested after 10 -18 months in different parts of the country. It has a fibrous root system which can penetrate as deep as 2.5 m in well-drained soils devoid of any restricting layer and salinity. Thus, the crop utilizes most of the moisture stored in the root -zone. In the major sugarcane growing areas, 2 -3 months dry and hot premonsoon period of the growing season is very crucial from the irrigation point of view. During this this period period the the young young crop crop is adver adversel sely y affec affected ted by severe severe soil soil moist moisture ure defic deficien iency cy and and excessively high soil temperature. In the rainy period, there is little need for irrigation unless the rains are too scanty and erratic. During post- monsoon growth period crop again needs irrigation adequately to meet its evapo-transpiration needs and in some cases to mitigate damage by frost. The life cycle of sugarcane plant is divided into four distinct phases namely germination phase (from planting to 60th day); formative phase (from 60th to 130th day); grand growth phas phase e (fro (from m 130t 130th h to 250t 250th h day) day) and and matu maturi rity ty phas phase e (250 (250th th to 365t 365th h day) day).. The The wate water r requireme requirement nt during during formativ formative e phase phase and grand growth growth phase phase is maximum maximum.. Generall Generally y under under north Indian condition, the water requirement of grand growth phase is met with rain, while the requirement of formative phase (during pre- monsoon period) has to be met through irrigation. The total water requirement for sugarcane varies from 200-300 centimeters. In northern India, autumn cane requires on an average 7 irrigations, 5 before monsoon and 2 after monsoon. Spring planted crops may be irrigated only six times. In drier climate and light soils, the crop may require 8 to 10 irrigations. In each irrigation, 3 acre inch of water should be applied. In Tarai areas, 2 to 3 irrigations before and one irrigation after monsoon are sufficient. Drainage is also equally important in waterlogged areas. Drain excess water from the sugarcane field if they are flooded during the rainy season. Due to waterlogged condition, the quality of cane deteriorates greatly. Drainage greatly helps in increasing the yield and sucrose content of the cane.
I. Groundnut Groun Groundn dnut ut is the the most most import importan antt oilsee oilseed d crop crop of the coun country try.. It is mainl mainly y grow grown n in Gujarat, Gujarat, Andhra Andhra Pradesh Pradesh.. Tamil Tamil Nadu, Nadu, Mahara Maharashtra shtra,, Karnat Karnataka, aka, Madhya Madhya Pradesh Pradesh,, Uttar Uttar Pradesh, Orissa, Rajasthan and Punjab. Raised as kharif crop in warm areas of relatively high rainfall, it often suffers from periodic water deficits during long rainless intervals. This occasional moisture deficiency is one of the important factors contributing to low yield of kharif groundnut. Consequently provision of irrigation to groundnut would greatly aid in improving its yield. Even now the farmers of southern states are growing groundnut during rabi as an irrigated crop. Being a rainy season crop, groundnut does not require irrigation. However, if dry spell occurs, irrigation may become necessary. One irrigation should be given at pod development stage. In the southern part of the country where groundnut is grown as rabi crop, 3-4 irrigations are necessa necessary. ry. Give the first first irrigatio irrigation n at the start of flowering flowering and subsequen subsequentt irrigatio irrigations ns when whenev ever er requ requir ired ed duri during ng the the frui fruiti ting ng peri period od to enco encour urag age e peg peg pene penetr trat atio ion n and and pod pod development. The last irrigation before harvesting will facilitate the full recovery of pods from the soil. J. Mustard and Rapeseed India is a major producer of mustard and rapeseed crops. These crops are primarily raised as rainfed crops during the rabi season on an area of 4.38 million hectares in Uttar Pradesh, Pradesh, Rajasthan, Rajasthan, Madhya Pradesh, Assam, Haryana, West Bengal, Bengal, Gujarat, Orissa, Punjab and BihaI. Due to low and uncertain rainfall during their growing season, these crops generally show favourable response to irrigations. It has been told that these crops need 1-4 irrigations, depending upon the soil moisture storage in the profile and the prevailing weather. Pre-bloom and pod filling stages are considered to be critical stages, therefore, irrigations at these stages are beneficial. K. Gram Gram is the most important pulse crop which is grown on an area of 3.5 million hectares mostl mostly y as a rainf rainfed ed rabi rabi crop crop in Madh Madhya ya Prad Prades esh, h, Rajas Rajastha than, n, Utta Uttarr Prad Pradesh esh,, Harya Haryana na,, Maharashtra, Punjab, Karnataka etc. The crop has a deep tap root system and can make an efficient use of the profile-stored water in the well-drained alluvial soils of northern states and retentive clay or clay loam soils of mid-west and southern states. Although, water requirements of the crop are relatively low, it often suffers from periodic water deficits owing to low and uncertain rains in the rabi season. Consequently, the average yield of the rainfed crop is low. With recent advancement in irrigation facilities, a part of rainfed area under gram can be brought under irrigation for improving its yield. Therefore, there is need to conduct studies to determine irrigation requirements of the crop in various agro- climatic region. If irrigation facilities are easily available, give a pre-sowing irrigation which will ensure proper proper germinat germination ion and smooth smooth crop growth. growth. If winter winter rains rains fail, fail, give one irrigatio irrigation n at preflowering stage and one at pod development stage. In no case first irrigation should be given earlier than four weeks after sowing. No irrigation should be given at flowering time. A light irriga irrigaito iton n shoul should d alwa always ys be given given beca because use heavy heavy ones ones are harmf harmful. ul. Exce Excess ss of irrig irrigati ation on enhances enhances vegetative growth and depresses the yield. L. Potato Potato is an important vegetable crop which has two growing seasons viz. autumn and spring. spring. Autumn potato is the main crop and sown sown in Septembe September-Oct r-Octobe oberr and harvested harvested in December- January. The crop requires frequent irrigations for optimum growth. A wet moisture
regime is conducive not only for adequate water availability to the crop but also keeps soil strength low which permits better development development of tubers. Potato crop requires frequent and light irrigations at low moisture tension, irrespective of the varieties. This is particularly important with new varieties which produce large sized tubers. It is therefore important to keep the ridges moist but not too wet which may be attained by giving irrigation at regular intervals. Accordingly, the first irrigation should be light and is given 7 -10 days days after after planting planting or even earlier depending depending upon soil moisture moisture content content.. the subsequent subsequent irrigation should be moderate to heavy which should cover 2/3rd to 3/4th height of the ridges. The intervals in subsequent irrigations could be about 15 days in heavy soils and 10 days in light soils. To complete its life cycle, the total water requirement of the crop about is 25 acre inch. Over-flooding results in soil compaction of the ridges which results into the poor aeration and poor tuber development. The crop should be given light irrigation if the frost is expected. The most critical stages for irrigation in potato are germination, stolon formation followed by earthing, tuber bulking which coincide 10 -12, 30 -35 and 55 -60 days after sowing. Moisture stress at these stages results in drastic reduction of tuber yields. Irrigation requirement for different crops under various climatic conditions and soil types are given in table 3. Table 3: Irrigation requirement for different crops Sl.No
Crop
Place
Soil type
Season
1
Wheat
Siruguppa (Karnataka) Jobner (Raj.) Hissar (Haryana) Ludhiana (Punjab)
Heavy black clay Loam sand Sandy loam Sandy loam
Rabi
Irrig. Requirement Number Amt (mm) 7 375
Rabi
6
405
Rabi
7
420
Rabi
5
360
3
220
Kharif
2-3
Kharif
5-6
Kharif
3
100150 300360 150
Black clay
Summer
10
510
Loamy loam Black clay
Summer
25
1250
Kharif
2
120
Sorghum
Hissar (Haryana) Arbhasi Arbhasi (Karnataka) Siruguppa (Karnataka) Bhavanisagar (T.N) Hyderabad (A.P) Dharwar
Sandy loam Sandy loam Sandy loam Clay loam
Rabi
Maize
Roorkee (U.P) Delhi
Loam
Kharif
5
360
2
3
to
(Karnataka) Siruguppa (Karnataka) Hyderabad (A.P) Coimbatore (T.N) Delhi 4
5
6
Bajra
Siruguppa (Karnataka) Hissar (Haryana) Delhi
Anand (Gujarat) Groundnut Dharwar (Karnataka) Hissar (Haryana) Chakuli (Orissa) Jabalpur (M.P.) Cotton Hissar
Sandy loam Black clay Sandy loam Sandy loam Sandy loam Black clay Sandy loam Loamy clay Black clay
Siruguppa Rahuri
Clay
Hyderabad
Black clay
Ludhiana
Coimbatore
Sandy loam Sandy loam Sandy loam Sandy loam Clay loam
Nawasti
Clay
Bhavani sagar
Sugarcane
Sandy loam Clay loam
Sandy loam Sandy loam Red sandy loam Clay
Delhi
7
clay Black clay
Roorkee Karnal Madhepura
Summer
1 -2
75-150
Rabi
4
300
Summer
4
300
Kharif
4
250
Kharif
2
150
Kharif
3
200
Kharif
2
150
Summer
10
500
July-Oct
5
360
July-Oct
4
300
-
690
3
225
4
50
3
210
11
725
6
640
2
150
11
640
8
620
11
660
8
600
10
500
14
1000
14
1750
Nov April JuneOct MaySept MaySept FebJune AugMarch JulyFeb Sept April Sept April MarchFeb DecJan DecJan FebDec DecJan
VII. Water Use Efficiency Since Since crops crops require require irrigatio irrigation n at differen differentt growth growth stages, stages, the scheduling scheduling of irrigatio irrigation n should be planned very systematically. In the early stages, crops require usually lesser amount of water and any excess water applied is either wasted or propagated through more vegetative growth instead of deeper root penetration. More water is required in tillering, flower formation and fruiting stages. When the soil is alkaline or saline or if the water contains more soluble salts. water water requir requireme ement nt is higher higher.. Need Need of water water varie varies s acco accordi rding ng to diffe differen rentt seas seasons ons.. tillag tillage e practices. vegetative growth, cropping system and land shapes, therefore, climatic conditions, genetic genetic variati variation on in plants, plants, agronom agronomic ic practices practices,, reductio reduction n of evapo-tra evapo-traspira spiration tion and water water stress, stress, fertilizer fertilizer applicat application, ion, plant plant protectio protection n measures measures includin including g weed control control become become the essential aspects in irrigation management. management. Since all these inputs determine yield productivity a proper synthesis among these may be necessary for an efficient system. Engineering concept expressed the efficiency in terms of net amount of water added to the root-zone or used in evapo-transpiration evapo-transpiration by a crop as a fraction of water diverted from some source. source. This This would would include include differen differentt forms forms of water water losses losses in conveya conveyance nce and application application.. Therefore, 100 x Normal consumptive use of water Water use use efficiency = -------------------------------------------------------------Net amount of water depleted from root zone soil This is the proportion between water delivered and that beneficially used. Since losses can occur during conveyance, application, storage and distribution, efficiency indexes could be measured during these different stages. Water delivered to the irrigated plot A. Water conveyance conveyance efficiency efficiency = 100 x ------------------------------------------------------------------------------------------Water diverted from the source Water stored in the root zone B. Water application application efficiency efficiency = 100 x --------------------------------------------------Water delivered to the field Water stored in the root zone C. Water storage storage efficiency efficiency = 100 x -------------------------------------------Water needed in the root zone prior to irrigation
D. Water distribution efficiency = 100 x (1 -y/d) Where, d = average depth of water stored along the run y = average numerical deviation from d The aim of economic irrigation is to maximize the financial return per unit of water applied or amount of money invested in the irrigation projects. Crop yield
WUE= --------------------------ET Where, WUE = water use efficiency ET = Evapo-transpiration Evapo-transpiration (water loss) Water Use Efficiency (WUE) is the ratio of crop yield to the amount of water depleted through evao-transpiration (ET). Water utilization by the crop is generally described in terms of kg of yield per hectare in millimetre. In the field, WUE would be the ratio of crop yield to total amou amount nt of wate waterr used used.. WUE WUE coul could d be incr increa ease sed d eith either er by incr increa easi sing ng the the crop crop yiel yield d or decreasing ET. Increasing crop protection is achieved through an integrated use of productive inputs. Decreasing ET requires adaptation of the plant varieties to the micro-environment and other genetic and climatic improvements. Optical irrigation and production efficiency should also be aimed in the economic evaluation of water use by crops. The The genet genetic ic varia variatio tion n in plant plants s influ influenc ence e WUE. WUE. Thos Those e plants plants with with higher higher rate rate of photosyn photosynthes thesis, is, usually usually have have higher higher WUE, WUE, ego maize, maize, sorghum, sorghum, bajra, bajra, ragi ragi and sugarcane. sugarcane. Most Most of the the pulses pulses,, oilsee oilseeds ds and and cerea cereals ls like like wheat wheat,, barle barley y and and oats oats have have lower lower rates rates of photosynthesis photosynthesis as well as WUE. It is also found that the new hybrids and modem varieties have higher rate of WUE, both from agronomic and climatological considerations. According to the WUE WUE and by comparison comparison among among the different different crops, one one may be able able to choose the crops to be cultivated. For this consider table-4. Table 4: Productivity or cereals per unit or water Sl.No
Crop (new varieties)
1 2 3 4 5
Rice Sorghum Bajra Maize Wheat
Water requirement Yield in a typi typica call tra tract (mm) 1200 4500 500 4500 500 4000 625 5000 400 5000
Water use efficiency (WUE) per mm water 3.7 9.0 8.0 8.0 12.5
Wheat has the highest productivity, followed by the millets and rice has the lowest water use efficiency (WUE). This may suggest the adoption of a non-paddy system, where all these crops are really competitive. But different regions have different cropping pattern and even similar cropping patterns may have different levels of productivity and water duty. Paddy is no doubt, a less productive user of water and any strict economic consideration may thwart its growth. The regional distribution may be such that paddy cultivation is specifically supported by climatic factors also. %%%%%%%%%%%%%%%%
