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Using the late spring nitrate test to reduce nitrate loss within a watershed
D B Jaynes1, D L Dinnes, D W Meek
1USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel Drive, Ames, IA 50011, USA. jaynes@nstl.gov
Journal of Environmental Quality
|April 13, 2004
Summary
Implementing the late spring nitrate test (LSNT) for corn significantly reduced nitrogen fertilizer use and decreased nitrate concentrations in surface water by over 30%. This practice offers a viable solution for improving water quality in agricultural regions.
Area of Science:
- Agricultural Science
- Environmental Science
- Water Quality Management
Background:
- Excessive nitrate (NO3) leaching from agricultural lands, particularly in the U.S. Corn Belt, exacerbates water quality issues and contributes to the Gulf of Mexico hypoxic zone.
- Current nitrogen (N) fertilizer management practices, often involving fall application of anhydrous ammonia, can lead to significant nitrate runoff.
Purpose of the Study:
- To evaluate the impact of the late spring nitrate test (LSNT) on nitrogen fertilizer application and surface water nitrate concentrations in a tile-drained corn-growing subbasin.
- To compare water quality outcomes between a subbasin using LSNT and adjacent subbasins with conventional N management.
Main Methods:
- A 400-ha tile-drained subbasin in central Iowa was treated with the LSNT method for corn (Zea mays L.) management.
- Surface water discharge and NO3 concentrations were monitored and compared between the LSNT-treated subbasin and two control subbasins over a four-year period (1997-2000).
- Autoregressive (AR) models were employed to analyze time series data of NO3 concentration differences.
Main Results:
- The LSNT method resulted in significant reductions in N fertilizer applications in two out of four years compared to farmers' standard practices.
- Corn yields were not significantly different between LSNT fields and nonlimiting N fertilizer check strips.
- Surface water NO3 concentrations in the LSNT subbasin were significantly lower than in control subbasins by the second year of the treatment period.
- Annual average flow-weighted NO3 concentrations were 11.3 mg N L(-1) for the LSNT subbasin and 16.0 mg N L(-1) for the control subbasins (1999-2000).
Conclusions:
- Widespread adoption of the LSNT program for N fertilizer management, especially where fall N application is common, can lead to a substantial decrease (> or = 30%) in surface water NO3 concentrations.
- The LSNT is an effective strategy for mitigating nitrate pollution from agricultural sources, thereby improving water quality and potentially reducing the expansion of hypoxic zones.