Crop Management and Corn Nitrogen Rate Effects on Nitrate Leaching

Abstract

Abstract Excess N use in crop production is often identified as a major contributor to NO 3 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 NO 3 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 NO 3 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 NO 3 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 NO 3 −N concentration at EONR was 18 mg L −1 . Average NO 3 −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 NO 3 −N leaching estimates based on water budget data and soil water NO 3 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 NO 3 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 NO 3 loss by leaching and N application rates that exceed crop needs.