Formulation and Estimation of Nitrate-Nitrogen Leaching from Corn Cultivation

Abstract

Although groundwater contamination by nitrate-nitrogen (NO3-N) can result from natural processes, an increased level of such contamination is usually attributed to agricultural activities. Using experimental data, 1987 through 1990, from three sites in southeastern Minnesota, this paper attempts to estimate a NO3-N leaching function to examine determinants of NO3-N leaching into groundwater and the effectiveness of a few selected best management practices (BMPs) in curtailing such deposition. The estimated results show that every year about 15% of applied N, 68% of residual NO3-N in the nonroot zone layer, and 20% of the residual NO3-N in the root zone layer are deposited into the groundwater. One kilogram per hectare corn (Zea mays L.) yield in the preceding year was found to reduce NO3-N level in the groundwater by about 2.33 g ha−1 in the succeeding year. A high rainfall year increased the level of NO3-N leaching. Among the BMPs, split-dose application of N was associated with a greater level of contamination while that of inhibitor use and no-tillage practices with a lowered level. Three policy implications can be drawn from this study. First, there appears to be a considerable residual NO3-N build-up in the soil profile in the study area. Because of N availability, especially in the root zone layers, appropriate credit should be given to utilization of this N when making N recommendations. Second, both nutrient and tillage management BMPs should be implemented to remove existing residual NO3-N from the root zone and to prevent it from further build-up. Third, periodic monitoring of residual NO3-N in the soil profile and contamination level in the groundwater are essential to measure the effectiveness of BMPs and regulate the use of N.