1. 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

2. 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:

3. 406, 407, 439 501, 502, 503, 504, 505 501, 502, 503, 504, 505 Magruder222Magruder222 801, 802, 803, 804 801, 802, 803, 804 Long-Term Soil Fertility Experiments

4. 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, 60-90 0-15, 15-30, 30-45, 45-60, 60-90 90-120, 120-150, 150-180, 90-120, 120-150, 150-180, 180-210, 210-240, 240-270 cm. 180-210, 210-240, 240-270 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, 60-90 0-15, 15-30, 30-45, 45-60, 60-90 90-120, 120-150, 150-180, 90-120, 120-150, 150-180, 180-210, 210-240, 240-270 cm. 180-210, 210-240, 240-270 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

5. Long-Term Experiments Exp. #Year # ofDateCrop Avg. Est.Reps.SampledYearsRainfall, Est.Reps.SampledYearsRainfall, mm mm 22219694July 199324922 40619654July 199328670 50219704July 199323771 50519703July 199323771 Long-Term Experiments Exp. #Year # ofDateCrop Avg. Est.Reps.SampledYearsRainfall, Est.Reps.SampledYearsRainfall, mm mm 22219694July 199324922 40619654July 199328670 50219704July 199323771 50519703July 199323771

6. 134134 00 4545 9090 179179 00100100200200300300400400 30306060 9090 120120 150150 180180 210210 240240 270270 300300 N Rate kg ha -1 SED = 15.41 NO 3 - -N, kg ha -1 Typic Paleustoll, 0-210 cm, #406 #406 00 4545 9090 134134 00100100200200300300400400 30306060 9090 120120 150150 180180 210210 240240 270270 300300 N Rate kg ha -1 SED = 3.29 NO 3 - -N, kg ha -1 Udertic Paleustoll, 0-240 cm, #222 Udertic Paleustoll, 0-240 cm, #222 Depth, cm

7. 00 2222 4545 6767 9090 112112 00100100200200300300400400 30306060 9090 120120 150150 180180 210210 240240 270270 300300 NO 3 - -N, kg ha -1 Udic Argiustoll, 0-240 cm, #502 Udic Argiustoll, 0-240 cm, #502 SED = 4.64 N Rate kg ha -1 0 0 34 67 134 269 N Rate kg ha -1 0010010020020030030040040030306060 9090 120120 150150 180180 210210 240240 270270 300300 SED = 48.71 NO 3 - -N, kg ha -1 Udic Argiustoll, 0-300 cm, #505 Udic Argiustoll, 0-300 cm, #505 Depth, cm

8. 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:

9. 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)

10. VolatilizationVolatilization DenitrificationDenitrification Leaching NH 3, N 2 NO 3 Microbial Pool NH 4 NO 3 NO 2 7-80 kg N/ha/yr NONO N2ON2ON2ON2O N2ON2ON2ON2O N2N2N2N2 N2N2N2N2 15-40 kg N/ha/yr NH 3 0-50 kg N/ha/yr UreaUrea Organic Immobilization 10-50 kg N/ha/yr 0-20 kg N/ha/yr Fertilizer N AppliedApplied 1 2 3 4 5 5 2 Olson and Swallow, 1984 Sharpe et al., 1988 Timmons and Cruse, 1990 Olson and Swallow, 1984 Sharpe et al., 1988 Timmons and Cruse, 1990 1 Mills et al., 1974 Matocha, 1976 DuPlessis and Kroontje, 1964 Terman, 1979 Sharpe et al., 1988 4 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, 1990 3 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)

11. NPKGrain Yield kg ha -1 Mg ha -1 kg ha -1 Mg ha -1 Experiment 222 029381.48 4529381.87 9029381.93 13429381.97 Experiment 406 0001.51 4520382.06 9020382.17 13420381.90 17920381.89 NPKGrain Yield kg ha -1 Mg ha -1 kg ha -1 Mg ha -1 Experiment 222 029381.48 4529381.87 9029381.93 13429381.97 Experiment 406 0001.51 4520382.06 9020382.17 13420381.90 17920381.89

12. NPKGrain Yield kg ha -1 Mg ha -1 kg ha -1 Mg ha -1 Experiment 502 020561.80 2220562.36 4520562.52 6720562.72 9020562.81 11220562.67 Experiment 505 029561.64 3429562.39 6729562.63 13429562.73 26929562.59 NPKGrain Yield kg ha -1 Mg ha -1 kg ha -1 Mg ha -1 Experiment 502 020561.80 2220562.36 4520562.52 6720562.72 9020562.81 11220562.67 Experiment 505 029561.64 3429562.39 6729562.63 13429562.73 26929562.59

13. 15001500 20002000 25002500 30003000 35003500 40004000 00100100200200300300 00 5050 100100 150150 200200 250250 4455111100 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

14. # 222 N rate, kg/ha Y1=1355 + 10.03x if x < 55.9 Y1= 1915 if x  55.9 r2= 0.88 Y2 =424 if x  104.1 Y2= -200 + 5.99x if x > 104.1 r2= 0.76 Grain yield, kg/ha Inorganic N Accumulation, kg/ha 0 0 20 40 60 80 100 120 140 1200 1400 1600 1800 2000 2200 300 350 400 450 500 550 600 650 700 y y 1 y y 2

15. Y1= 1430 + 11.38x if x < 47.4 Y1 = 1970 if x  47.4 r2= 0.90 Y2 = 439 if x  75.1 Y2=211 + 3.04x if x > 75.1 r2 = 0.92 # 406 0 0 50 100 150 200 1200 1400 1600 1800 2000 2200 2400 400 500 600 700 800 y y 1 y y 2 Grain yield, kg/ha Inorganic N Accumulation, kg/ha N rate, kg/ha

16. 15001500 20002000 25002500 30003000 35003500 40004000 00100100200200300300 00 5050 100100 150150 200200 250250 3535 6464 109109 4545 Grain Yield, kg/ha Profile N Accumulation, kg/ha N Rate, kg/ha

17. 0 0 20 40 60 80 100 120 140 20 30 40 50 60 70 80 # 222 N rate, kg/ha Grain N Uptake, kg/ha Y = 29.7 + 0.28x - 0.00055x2 r2=0.90 9.4 =19%

18. 5.3 = 19% # 406 N rate, kg/ha Grain N Uptake, kg/ha Y = 33.1 + 0.40x - 0.0017x2 r2=0.89 0 0 20 40 60 80 100 120 140 160 180 200 20 30 40 50 60 70 80

19. 0.040.04 0.050.05 0.060.06 0.070.07 0.080.08 0.090.090.10.100303060609090120120150150 0.40.4 0.50.5 0.60.6 0.70.7 0.80.80.90.9TSNTSN OCOC #222#222 Total Soil N, % Organic Carbon, % N Rate, kg/ha SED TSN = 0.004 SED OC = 0.03

20. 0.040.04 0.050.05 0.060.06 0.070.07 0.080.08 0.090.09 0.10.1 0040408080120120160160200200 0.40.4 0.50.5 0.60.6 0.70.7 0.80.8 0.90.9 TSNTSN OCOC #406#406 Total Soil N, % Organic Carbon, % N Rate, kg/ha SED TSN = 0.002 SED OC = 0.03

21. 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

22. 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

23. Fertilizer NH 4, NO 3 Organic Matter Pool InorganicNitrogenInorganicNitrogen