Soil-Plant Inorganic Nitrogen Buffering W.R. Raun, G.V. Johnson, H. Sembiring, E.V. Lukina, J.M. LaRuffa, W.E. Thomason, S.B. Phillips, J.B. Solie, M.L. Stone and R.W. Whitney OKLAHOMA STATE UNIVERSITY 94th ASHS International Conference Salt Lake City, Utah, July 26, 1997 W.R. Raun, G.V. Johnson, H. Sembiring, E.V. Lukina, J.M. LaRuffa, W.E. Thomason, S.B. Phillips, J.B. Solie, M.L. Stone and R.W. Whitney OKLAHOMA STATE UNIVERSITY 94th ASHS International Conference Salt Lake City, Utah, July 26, 1997

l To evaluate the relationship between relative wheat grain yield and NO 3 -N accumulation as a function of applied N in soil profiles of long-term experiments. l To evaluate the presence of inorganic N buffering in soils using linear-plateau and plateau-linear models of N rate versus grain yield and soil profile inorganic N accumulation. l To evaluate the relationship between relative wheat grain yield and NO 3 -N accumulation as a function of applied N in soil profiles of long-term experiments. l To evaluate the presence of inorganic N buffering in soils using linear-plateau and plateau-linear models of N rate versus grain yield and soil profile inorganic N accumulation. Objectives:Objectives:

406, 407, , 502, 503, 504, , 502, 503, 504, 505 Magruder222Magruder , 802, 803, , 802, 803, 804 Long-Term Soil Fertility Experiments

Procedures: Deep soil cores 4.4cm in diameterDeep soil cores 4.4cm in diameter 0-270cm sampling depth0-270cm sampling depth 0-15, 15-30, 30-45, 45-60, , 15-30, 30-45, 45-60, , , , , , , , , cm , , cm. 2M KCl extract (Bremner, 1965)2M KCl extract (Bremner, 1965) NO 3 -N (Cd reduction, Jackson et al., 1975)NO 3 -N (Cd reduction, Jackson et al., 1975) NH 4 -N (phenolate method, Lachat Inst., 1990NH 4 -N (phenolate method, Lachat Inst., 1990Procedures: Deep soil cores 4.4cm in diameterDeep soil cores 4.4cm in diameter 0-270cm sampling depth0-270cm sampling depth 0-15, 15-30, 30-45, 45-60, , 15-30, 30-45, 45-60, , , , , , , , , cm , , cm. 2M KCl extract (Bremner, 1965)2M KCl extract (Bremner, 1965) NO 3 -N (Cd reduction, Jackson et al., 1975)NO 3 -N (Cd reduction, Jackson et al., 1975) NH 4 -N (phenolate method, Lachat Inst., 1990NH 4 -N (phenolate method, Lachat Inst., 1990

Long-Term Experiments Exp. #Year # ofDateCrop Avg. Est.Reps.SampledYearsRainfall, Est.Reps.SampledYearsRainfall, mm mm July July July July Long-Term Experiments Exp. #Year # ofDateCrop Avg. Est.Reps.SampledYearsRainfall, Est.Reps.SampledYearsRainfall, mm mm July July July July

N Rate kg ha -1 SED = NO 3 - -N, kg ha -1 Typic Paleustoll, cm, #406 # N Rate kg ha -1 SED = 3.29 NO 3 - -N, kg ha -1 Udertic Paleustoll, cm, #222 Udertic Paleustoll, cm, #222 Depth, cm

NO 3 - -N, kg ha -1 Udic Argiustoll, cm, #502 Udic Argiustoll, cm, #502 SED = 4.64 N Rate kg ha N Rate kg ha SED = NO 3 - -N, kg ha -1 Udic Argiustoll, cm, #505 Udic Argiustoll, cm, #505 Depth, cm

l Ability of the soil-plant system to limit the amount of inorganic N accumulation in the rooting profile when N fertilization rates exceed that required for maximum grain yields. Inorganic Nitrogen Buffering:

Nitrogen Buffering Mechanisms ( N in excess of that needed for maximum yield ) 4Plant NH 3 loss increases with higher rates of applied N 4Increased forage N 4Increased organic C 4Increased grain protein 4Increased denitrification 4Increased volatilization (urea) 4Plant NH 3 loss increases with higher rates of applied N 4Increased forage N 4Increased organic C 4Increased grain protein 4Increased denitrification 4Increased volatilization (urea)

VolatilizationVolatilization DenitrificationDenitrification Leaching NH 3, N 2 NO 3 Microbial Pool NH 4 NO 3 NO kg N/ha/yr NONO N2ON2ON2ON2O N2ON2ON2ON2O N2N2N2N2 N2N2N2N kg N/ha/yr NH kg N/ha/yr UreaUrea Organic Immobilization kg N/ha/yr 0-20 kg N/ha/yr Fertilizer N AppliedApplied Olson and Swallow, 1984 Sharpe et al., 1988 Timmons and Cruse, 1990 Olson and Swallow, 1984 Sharpe et al., 1988 Timmons and Cruse, Mills et al., 1974 Matocha, 1976 DuPlessis and Kroontje, 1964 Terman, 1979 Sharpe et al., Aulackh et al., 1984 Colbourn et al., 1984 Bakken et al., 1987 Prade and Trolldenier, 1990 Aulackh et al., 1984 Colbourn et al., 1984 Bakken et al., 1987 Prade and Trolldenier, Francis et al., 1993 Hooker et al., 1980 O’Deen, 1986, 1989 Daigger et al., 1976 Parton et al., 1988 Francis et al., 1993 Hooker et al., 1980 O’Deen, 1986, 1989 Daigger et al., 1976 Parton et al., 1988 Chaney, 1989 Sommerfeldt and Smith, 1973 Macdonald et al., 1989 Kladivko, 1991 Chaney, 1989 Sommerfeldt and Smith, 1973 Macdonald et al., 1989 Kladivko, 1991 NH 4 +OH - NH 3 + H 2 O N Buffering Mechanisms NH 4 fixation (physical)

NPKGrain Yield kg ha -1 Mg ha -1 kg ha -1 Mg ha -1 Experiment Experiment NPKGrain Yield kg ha -1 Mg ha -1 kg ha -1 Mg ha -1 Experiment Experiment

NPKGrain Yield kg ha -1 Mg ha -1 kg ha -1 Mg ha -1 Experiment Experiment NPKGrain Yield kg ha -1 Mg ha -1 kg ha -1 Mg ha -1 Experiment Experiment

Inorganic Nitrogen Buffering Profile N accumulation, kg/ha Grain yield, kg/ha N Rate, kg/ha SafetyZone N rate where maximum yields are obtained N rate where maximum yields are obtained Grain Yield Soil profile NO3-N accumulation Grain Yield Soil profile NO3-N accumulation N rate where nitrate begins to accumulate below the root zone

# 222 N rate, kg/ha Y1= x if x < 55.9 Y1= 1915 if x  55.9 r2= 0.88 Y2 =424 if x  Y2= x if x > r2= 0.76 Grain yield, kg/ha Inorganic N Accumulation, kg/ha y y 1 y y 2

Y1= x if x < 47.4 Y1 = 1970 if x  47.4 r2= 0.90 Y2 = 439 if x  75.1 Y2= x if x > 75.1 r2 = 0.92 # y y 1 y y 2 Grain yield, kg/ha Inorganic N Accumulation, kg/ha N rate, kg/ha

Grain Yield, kg/ha Profile N Accumulation, kg/ha N Rate, kg/ha

# 222 N rate, kg/ha Grain N Uptake, kg/ha Y = x x2 r2= =19%

5.3 = 19% # 406 N rate, kg/ha Grain N Uptake, kg/ha Y = x x2 r2=

TSNTSN OCOC #222#222 Total Soil N, % Organic Carbon, % N Rate, kg/ha SED TSN = SED OC = 0.03

TSNTSN OCOC #406#406 Total Soil N, % Organic Carbon, % N Rate, kg/ha SED TSN = SED OC = 0.03

Conclusions: Nitrogen fertilization rates which significantly increased inorganic profile N accumulation, exceeded that required for maximum yields by more than 20 kg N ha -1 in all experiments. Nitrogen fertilization rates which significantly increased inorganic profile N accumulation, exceeded that required for maximum yields by more than 20 kg N ha -1 in all experiments. Soil organic matter levels increased when N rates exceeded that required for maximum yield Soil organic matter levels increased when N rates exceeded that required for maximum yield Use of fertilizer N at rates equal or less than that required to meet crop needs did not increase inorganic N accumulation Use of fertilizer N at rates equal or less than that required to meet crop needs did not increase inorganic N accumulationConclusions: Nitrogen fertilization rates which significantly increased inorganic profile N accumulation, exceeded that required for maximum yields by more than 20 kg N ha -1 in all experiments. Nitrogen fertilization rates which significantly increased inorganic profile N accumulation, exceeded that required for maximum yields by more than 20 kg N ha -1 in all experiments. Soil organic matter levels increased when N rates exceeded that required for maximum yield Soil organic matter levels increased when N rates exceeded that required for maximum yield Use of fertilizer N at rates equal or less than that required to meet crop needs did not increase inorganic N accumulation Use of fertilizer N at rates equal or less than that required to meet crop needs did not increase inorganic N accumulation

Conclusions Research results have documented increased Research results have documented increased plant N loss grain protein denitrification soil organic C forage/straw N when N rates exceed that required for maximum yield Soil-plant inorganic N buffering is present in all production systems but is unlikely to be important when N rates continuously exceed twice that required Soil-plant inorganic N buffering is present in all production systems but is unlikely to be important when N rates continuously exceed twice that requiredConclusions Research results have documented increased Research results have documented increased plant N loss grain protein denitrification soil organic C forage/straw N when N rates exceed that required for maximum yield Soil-plant inorganic N buffering is present in all production systems but is unlikely to be important when N rates continuously exceed twice that required Soil-plant inorganic N buffering is present in all production systems but is unlikely to be important when N rates continuously exceed twice that required

Fertilizer NH 4, NO 3 Organic Matter Pool InorganicNitrogenInorganicNitrogen