Nitrate Leaching and Nitrogen Budget as Affected by Maize Nitrogen Rate and Soil Type

Abstract

AbstractLeaching loss as nitrate (NO3) is a growing concern because of its potential effect on water resources. Leaching of NO3 with drainage water from subsurface‐drained field plots seeded to maize (Zea mays L.) in 1992, 1993, and 1994 was measured on two soil types (a clay loam and a loamy sand) and for three N fertilization rates (22, 100, and 134 kg N ha−1). The 100 kg ha−1 rate was based on the results of a presidedress nitrate test (PSNT). Nitrate nitrogen (NO3‐N) leaching was similar between fertilizer N treatments at both sites in 1992, the first year after sod plowdown, but concentrations were greater than 10 mg L−1. For the subsequent two years, losses were similar for the 22 kg N ha−1 and the PSNT‐based treatments, but significantly higher for the 134 kg N ha−1 treatment on the clay loam. On the loamy sand, losses increased from the lowest to the highest N rate. Nitrate leaching losses were consistently higher on the loamy sand than on the clay loam. The N budget results showed that the 134 kg N ha−1 rate had the highest residual soil NO3‐N in the three years at both sites. On the clay loam, significant N losses occurred from denitrification following alfalfa plowdown and the subsequent fall and spring. Results indicate that N use efficiency rapidly decreases with overfertilization, even with N fertilization rates that only slightly exceed (134%) crop requirements. The PSNT‐based rate reduced N leaching losses while maintaining maize yields.