Soil-Plant Inorganic Nitrogen Buffering

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

2. Objectives: • To evaluate the relationship between relative wheat grain yield and NO3-N accumulation as a function of applied N in soil profiles of long-term experiments. • 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.

3. Long-Term Soil Fertility Experiments 501, 502, 503, 504, 505 Magruder 222 801, 802, 803, 804 406, 407, 439

4. Procedures: • Deep soil cores 4.4cm in diameter • 0-270cm sampling depth • 0-15, 15-30, 30-45, 45-60, 60-90 • 90-120, 120-150, 150-180, • 180-210, 210-240, 240-270 cm. • 2M KCl extract (Bremner, 1965) • NO3-N (Cd reduction, Jackson et al., 1975) • NH4-N (phenolate method, Lachat Inst., 1990

5. Long-Term Experiments Exp. # Year # of Date Crop Avg. Est. Reps. Sampled Years Rainfall, mm 222 1969 4 July 1993 24 922 406 1965 4 July 1993 28 670 502 1970 4 July 1993 23 771 505 1970 3 July 1993 23 771

6. 100 200 300 400 100 200 300 400 0 0 30 30 60 60 90 90 120 120 150 150 180 180 210 210 240 240 270 270 300 300 Udertic Paleustoll, 0-240 cm, #222 Typic Paleustoll, 0-210 cm, #406 NO3--N, kg ha-1 NO3--N, kg ha-1 SED = 15.41 SED = 3.29 Depth, cm Depth, cm N Rate kg ha-1 N Rate kg ha-1 0 0 45 45 90 90 134 134 179

7. 30 100 200 300 400 0 30 60 60 90 90 120 150 120 180 150 N Rate kg ha-1 210 180 0 240 210 34 270 240 67 300 270 134 300 269 Udic Argiustoll, 0-240 cm, #502 Udic Argiustoll, 0-300 cm, #505 NO3--N, kg ha-1 NO3--N, kg ha-1 0 100 200 300 400 SED = 4.64 N Rate kg ha-1 0 Depth, cm Depth, cm 22 SED = 48.71 45 67 90 112

8. Inorganic Nitrogen Buffering: • 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.

9. Nitrogen Buffering Mechanisms(N in excess of that needed for maximum yield) • Plant NH3 loss increases with higher rates of applied N • Increased forage N • Increased organic C • Increased grain protein • Increased denitrification • Increased volatilization (urea)

10. 1 Mills et al., 1974 Matocha, 1976 DuPlessis and Kroontje, 1964 Terman, 1979 Sharpe et al., 1988 N Buffering Mechanisms 1 4 0-50 kg N/ha/yr 15-40 kg N/ha/yr NH3 NH4+OH- NH3 + H2O Fertilizer N NO Volatilization N2O Urea Applied N2 3 NH4 fixation (physical) Denitrification 7-80 kg N/ha/yr NH3, N2 10-50 kg N/ha/yr 2 Microbial Pool Organic Immobilization NH4 NO3 NO2 5 Chaney, 1989 Sommerfeldt and Smith, 1973 Macdonald et al., 1989 Kladivko, 1991 NO3 5 Leaching 2 3 4 0-20 kg N/ha/yr Olson and Swallow, 1984 Sharpe et al., 1988 Timmons and Cruse, 1990 Francis et al., 1993 Hooker et al., 1980 O’Deen, 1986, 1989 Daigger et al., 1976 Parton et al., 1988 Aulackh et al., 1984 Colbourn et al., 1984 Bakken et al., 1987 Prade and Trolldenier, 1990

11. N P K Grain Yield kg ha-1 Mg ha-1 Experiment 222 0 29 38 1.48 45 29 38 1.87 90 29 38 1.93 134 29 38 1.97 Experiment 406 0 0 0 1.51 45 20 38 2.06 90 20 38 2.17 134 20 38 1.90 179 20 38 1.89

12. N P K Grain Yield kg ha-1 Mg ha-1 Experiment 502 0 20 56 1.80 22 20 56 2.36 45 20 56 2.52 67 20 56 2.72 90 20 56 2.81 112 20 56 2.67 Experiment 505 0 29 56 1.64 34 29 56 2.39 67 29 56 2.63 134 29 56 2.73 269 29 56 2.59

13. Inorganic Nitrogen Buffering N rate where maximum yields are obtained Grain Yield Soil profile NO3-N accumulation 250 4000 200 3500 Safety Zone 150 3000 Profile N accumulation, kg/ha Grain yield, kg/ha 100 2500 2000 50 1500 0 0 100 200 300 N Rate, kg/ha N rate where nitrate begins to accumulate below the root zone 4 5 1 1 0

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

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

16. 250 4000 45 200 3500 150 3000 Grain Yield, kg/ha Profile N Accumulation, kg/ha 100 2500 109 50 2000 1500 0 0 100 200 300 35 N Rate, kg/ha 64

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

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

19. 0.1 0.9 0.09 0.8 0.08 0.7 0.07 0.6 0.06 0.5 0.05 0.04 0.4 #222 TSN OC Total Soil N, % Organic Carbon, % SED TSN = 0.004 SED OC = 0.03 0 30 60 90 120 150 N Rate, kg/ha

20. #406 0.1 0.9 0.09 0.8 0.08 0.7 Total Soil N, % 0.07 Organic Carbon, % 0.6 0.06 TSN SED TSN = 0.002 0.5 0.05 OC SED OC = 0.03 0.04 0.4 0 40 80 120 160 200 N Rate, kg/ha

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. • 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

22. Conclusions • 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

23. NH4, NO3 Fertilizer Organic Matter Pool Inorganic Nitrogen