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

Abstract

Abstract Leaching loss as nitrate (NO 3 ) is a growing concern because of its potential effect on water resources. Leaching of NO 3 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 (NO 3 ‐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 NO 3 ‐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.