1Soil Nitrate Nitrogen
KCl Extraction / Cd-Reduction Method Robert Miller and Leticia Sonon
Application and Principle This method inoles the !uantitatie extraction o" nitrate nitrogen #N$%-N& "rom soils using '() M KCl( Nitrate is determined determined *+ reduction to nitrite nitrite #N$'-N& ia a cadmium reactor, diaotied .ith sul"anilamide and is coupled to N-#1-Napth+l&-eth+lenediamine dih+drochloride to "orm an aochromophore #red-purple in color& measured spectrophotometricall+ at ') nm( The method is readil+ adapted to manual or automated techni!ues( The procedure "ollo.s that o" Keene+ and Nelson #10'& "or determining nitrate nitrogen .ith a modi"ication in .hich ' m2 o" KCl and () g o" soil soil are used instead o" 1)) m2 and 1) g soil( Extending the sha3ing period to thirt+ minutes .ith '() M KCl #4remner and Keene+, 105& permits the simultaneous extraction o" ammonium and nitrate( nitrate( Care must *e ta3en to aoid contamination "rom "ilter paper and operator handling( Since cadmium is a haardous material, "ollo. manu"acturer6s recommendations to properl+ handle this material( material( Soil N$%-N is aaila*le to plant upta3e, there"ore, it can *e credited credited .hen determining crop nitrogen needs( The method detection limit is approximatel+ )( mg 3g-1 #on a dr+ soil *asis& and is generall+ reproduci*le 7 58(
E!uipment 1( Anal+tical Anal+tical *alance, *alance, 1))() 1))() g capacit capacit+, +, resolut resolution ion 7 )()1 g '( Repipe Repipette tte dispe dispense nser, r, cali*r cali*rated ated to to '() 7 )(' )(' m2 %( Reciprocatin Reciprocating g horiontal horiontal mechanical mechanical sha3er, sha3er, capa*le capa*le o" 1) 1) oscillatio oscillations ns per minute minute #opm& 9( Extraction essels and associated associated "iltration essel ( :hatman No( 9' or e!uialent highl+ retentie "ilter "ilter paper 5( Spectrophotometer, autoanal+er, autoanal+er, or "lo. in;ection in;ection anal+er #<=A& instrument
Reagents 1( >eioni >eionied ed .ater, .ater, ASTM ASTM T+pe T+pe = grade grade '( Potassium Potassium chloride chloride extrac extracting ting soluti solution, on, '() M KCl? >issole >issole 1) g o" reagent reagent grade grade KCl in )) m2 deionied .ater and dilute to a 1))) m2 #See Comment @1&
%( Standard cali*ration solutions o" N$%-N( Prepare six cali*ration standards ranging "rom )(1 to ')() mg 2-1 in '() M KCl extraction solution prepared "rom 1))) mg 2-1 N$%-N standard solution(
Procedure 1( :eigh or scoop () 7 )() g o" air-dried soil puleried to pass 1) mesh siee # '() mm& into extraction essel( Add '() m2 o" '() M KCl extraction solution using repipette dispenser #See Comment @'&( =nclude a method *lan3( '( Place extraction essel#s& on reciprocating mechanical sha3er and sha3e "or thirt+ #%)& minutes( %( etermine nitrate concentration o" KCl extract, method *lan3, un3no.n samples and record results as mg 2-1 o" nitrate in extract solution #See Comment @&(
Calculation 1(
N$%-N mg 3g-1 in soil #N$%-N mg 2-1 in "iltrate - method *lan3& D
'( Report soil nitrate nitrogen concentration to the nearest )(1 mg 3g-1 #See Comment @5&(
Precision and Accurac+ 1(
Soil N$%-N measurements can *e made to the nearest )(1 mg 3g-1(
'(
T+pical measurements o" inter-la*orator+ precision "or soil N$%-N are sho.n *elo.( Sample 1
Mean mg 3g-1
Standard deiation mg 3g-1
SRS - 1))%
9(5
)(%
SRS - 1))5
11(9
)(5
SRS - 1))
'9(5
)(0
SRS - 1)1)
95(%
1('
1
>ata "rom ')1) A2P Program, *ased on three replications(
=nter"erences 1( N nitrite #N$'-N& in soil .ill result in a positie inter"erence( =t is er+ unli3el+ that soil samples that hae *een thoroughl+ dried .ill contain N$'-N( To eri"+ concentration repeat extraction and anal+ed extract "or N$'-N .ithout the use o" the cadmium reduction column(
E""ects o" Storage 1( Air-dried soils ma+ *e stored seeral months .ithout a""ecting the soil nitrate proided the+ are stored in an moisture "ree enironment(
Sa"et+ and disposal 1( The chemicals used in this procedure pose no sa"et+ ris3 and there"ore can *e stored and disposed o" according to routine la*orator+ procedures(
Comments 1(
Soils can *e extracted .ith 1() M KCl #Kachurina et al(, '))&(
'(
Chec3 repipette dispensing olume cali*ration using an anal+tical *alance(
%( Chec3 "ilter paper suppl+ "or possi*le contamination o" N$%-N( =" contamination is greater than )(' mg 2-1 on a solution *asis, rinse "ilter paper .ith '() M KCl( 9( Soil KCl extract ma+ *e stored up to three .ee3s i" stored at 9oC and/or .ith 1)) u2 o" toluene or th+mol( ( Samples haing nitrate concentrations exceeding the highest standard .ill re!uire dilution and reanal+sis( 5( Nitrate-nitrogen #N$%-N& results can *e expressed on a olume *asis( Assuming the sample represents a )-5 inch #)-1 cm& depth o" the soil, then? N$%-N mg 3g-1 D '() ≅ N$%-N l*s ac-1
Re"erences 4remmer, ( M( and >(R( Keene+( 105( >etermination and isotopic ratio anal+sis o" di""erent "orms o" nitrogen in soils? =( Apparatus and procedure "or distillation "or and determination o"
ammonium( Soil Sci( Soc( Am( Proc( '0?)9-)B( >ahn3e, :(C( 100)( Testing soils "or aaila*le nitrogen( p( 1')-19)( =n? R(2( :esterman #ed(& Soil testing and plant anal+sis( Soil Sci( Soc( Am( 4oo3 series % ASA Madison :=( >orich, R( A( and >( :( Nelson( 109( Ealuation o" manual cadmium reduction methods "or determination o" nitrate in potassium chloride extracts o" soils( Soil Sci( Soc Am ( 9?B'-B( Felderman, R(G( and P(E( ahn3e #ed(& Recommended chemical soil test procedures "or the North Central Region( North >a3ota Agr( Expt( Sta( 4ulletin No( 900 #reised&( Kachurina, $(M(, G( Hhang, :(R( Raun, and E(F( Krener( ')))( Simultaneous determination o" soil aluminum, ammonium- and nitrate-nitrogen using 1 M potassium chloride ex traction( Commun( Soil Sci( and Pl( Anal( %1? 0%-0)%( Keene+, >(R( and >(:( Nelson( 10'( Nitrogen - inorganic "orms( =n A(2( Page #eds(& Methods o" soil anal+sis, part '( Agron( Monogr( 0, 'nd ed( ASA and SSSA, Madison, :=( p( 59%-50(
