Crop Management and Corn Nitrogen Rate Effects on Nitrate Leaching
- T. W. Andraski *,
- L. G. Bundy and
- K. R. Brye
Excess N use in crop production is often identified as a major contributor to NO3 enrichment of ground water. Little information is available to show the specific relationships between crop management systems and N fertilizer use on the amounts of NO3 lost by leaching. This study determined the effect of several cropping systems and N rates, providing a range of N availability to corn (Zea mays L.), on soil water NO3 concentrations and leaching below the root zone. Four cropping-manure management systems were established in 1993 and 1994 (8-site years) at Arlington, WI, on a Plano silt loam (fine-silty, mixed, superactive, mesic Typic Argiudoll). Ammonium nitrate (0 to 204 kg N ha−1 in 34-kg increments) was broadcast at the time of corn planting. Economic optimum N rates (EONR) for corn ranged from 0 to 150 kg ha−1 depending on site-year. Soil water NO3 concentrations were determined for 18-mo using porous-cup samplers installed at a 120-cm depth in the 0 and 204 kg N ha−1 treatments. Nitrate N concentrations in the samplers increased as the amount of N applied in excess of the observed EONR increased. Predicted soil water NO3−N concentration at EONR was 18 mg L−1. Average NO3−N concentrations were <10 mg L−1 where fertilizer N rates were >50 kg N ha−1 below the EONR and >20 mg L−1 where fertilizer N rates were >50 kg N ha−1 above the EONR. Total NO3−N leaching estimates based on water budget data and soil water NO3 concentrations for the 18-mo study period ranged from 3 to 88 kg ha−1 depending on crop and manure management system, N fertilizer rate, amount of water drainage, and time of drainage event relative to treatment establishment. An end-of-season soil NO3 test appears to be capable of evaluating corn N management practices and indicating the amount of excess N fertilizer applied that may be leached from the root zone. These results illustrate the direct relationship between NO3 loss by leaching and N application rates that exceed crop needs.
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