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Jason R. Vogel 1 , Glenn O. Brown 1 , John S. Tyner 1 , Jurgen Garbrecht 2

Nitrate Flux Under Long-Term Wheat Fields. Jason R. Vogel 1 , Glenn O. Brown 1 , John S. Tyner 1 , Jurgen Garbrecht 2 1 Oklahoma State University, Stillwater, OK, USA 2 USDA-ARS Grazinglands Research Station, El Reno, OK, USA 1999 American Geophysical Union Summer Meeting

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Jason R. Vogel 1 , Glenn O. Brown 1 , John S. Tyner 1 , Jurgen Garbrecht 2

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  1. Nitrate Flux Under Long-Term Wheat Fields Jason R. Vogel 1, Glenn O. Brown 1, John S. Tyner 1, Jurgen Garbrecht 2 1 Oklahoma State University, Stillwater, OK, USA 2 USDA-ARS Grazinglands Research Station, El Reno, OK, USA 1999 American Geophysical Union Summer Meeting Boston, MA, June 2, 1999

  2. Objective Test Raun’s Soil Plant Buffer theory, which holds that any nitrate applied up to the point of dryland wheat maximum yield, will not leach to ground water.

  3. Justification • 5.2 million acres in Oklahoma in wheat production. • 60% of the total harvested acreage and 12% of the total state land area. • Large amounts of nitrogen are used as fertilizer in wheat production.

  4. Soil-Plant Buffer • Proposed by Dr. William Raun • Root zone provides a “buffer” for N • Not a process or property per se • Implies that producers can safely apply rates necessary to insure maximum yields. • Controversial theory which goes against some conventional wisdom and other published research.

  5. Long-Term Plots • Operated by the OSU Soil and Plant Sciences Department. • Dryland winter wheat planted continuously for 28 years with constant rates of 0 to 134 kg/ha NO3-N and uniform 45 kg/ha K2O (as KCl). • Plot dimensions 20’ x 60’. • Have had time to equilibrate to their respective management.

  6. Long-Term Plots Treatment 1 0 kg/ha 2 45 kg/ha 3 90 kg/ha 4 134 kg/ha Max Yield @ 73 kg/ha 3 2 1 4 2 3 1 4 REP I REP II 2 1 3 4 3 1 2 4 REP III REP IV

  7. Sampling • 67 mm (2-5/8 in) cores collected to approximately 2.5 m depth. • Sectioned and sealed in field.

  8. Analysis • Analyzed in the lab for • water content, • NO3-N, • chloride, • particle size, and • bulk density.

  9. Particle Size

  10. Dry Bulk Density

  11. Moisture Content

  12. Moisture Content Treatment M.C. t test 1 (0 kg/ha) 27.0 % X 2 (45 kg/ha) 26.9 % X 3 (90 kg/ha) 29.4 % * 4 (134 kg/ha) 28.4 % *

  13. Nitrate-N Concentration

  14. Nitrate-N Concentration Treatment Nitrate-N t test 1 (0 kg/ha) 4.4 mg/L X 2 (45 kg/ha) 4.4 mg/L X 3 (90 kg/ha) 8.6 mg/L 4 (134 kg/ha) 32.2 mg/L

  15. Water Flux by Cl- Balance

  16. Water Flux Treatment Flux t test 1 (0 kg/ha) 1.6 cm/yr X 2 (45 kg/ha) 2.1 cm/yr 3 (90 kg/ha) 1.5 cm/yr X 4 (134 kg/ha) 4.0 cm/yr

  17. Nitrate Mass Flux

  18. Nitrate Mass Flux(mg/cm2/yr) Treatment Flux t test 1 (0 kg/ha) 0.008 X 2 (45 kg/ha) 0.010 X 3 (90 kg/ha) 0.012 X 4 (134 kg/ha) 0.121

  19. Summary • Concentration measurements indicate • equivalent concentrations of nitrate-N under 0 and 45 kg/haNO3-Nplots • increased nitrate-N concentrations under 90 kg/haNO3-N plots, but still below drinking water standard • greatly increased nitrate-N concentrations under 134 kg/haNO3-N plots

  20. Summary • Water flux calculations indicate • increased recharge rate under 134 kg/ha NO3-N plots • Nitrate mass flux calculations indicate • equivalent small mass transport under 0, 45, and 90 kg/ha NO3-N plots • significant mass transport below 134 kg/ha NO3-N plots (9% of applied nitrate)

  21. Conclusion • Results support Raun’s Soil-Plant Buffer theory. Nitrate application up to maximum grain yield on dryland wheat does not increase nitrate leaching to the ground water.

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