Nitrate leaching and nitrogen budget as affected by maize nitrogen rate and soil type

Leaching loss as nitrate (NO3) is a growing concern because of its potentia l effect on water resources. Leaching of NO3 ffith drainage water from subs urface-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). Ni trate nitrogen (NO3-N) teaching was similar between fertilizer N treatments at both sites in 1992, the first year after sod plowdown, but concentratio ns were greater than 10 mg L-1. For the subsequent two Sears, losses were s imilar for the 22 kg N ha(-1) and the PSNT-based treatments, but significan tly higher for the 133 kg N ha(-1) treatment on the clay loam. On the loamy sand, losses increased from the lowest to the highest N rate. Nitrate leac hing losses were consistently higher on the loamy sand than on the clay loa m, The N budget results showed that the 133 kg N ha(-1) rate had the highes t residual soil NO3-N in the three gears at both sites. On the clay loom, s ignificant N losses occurred from denitrification following alfalfa plowdow n and the subsequent fall and spring. Results indicate that N use efficienc y rapidly decreases with overfertilization, even with N fertilization rates that only slightly exceed (134%) crop requirements. The PSNT-based rate re duced N leaching losses while maintaining maize yields.