Assessment of subsurface drainage management practices to reduce nitrogen loadings using AnnAGNPS

The goal of the Future Midwest Landscape project is to quantify current and future landscape services across the Midwest region and examine changes expected to occur as a result of two alternative drivers of future change: the growing demand for biofuels; and hypothetical increases in incentives for the use of agricultural conservation practices to mitigate the adverse impact caused by the growing demand for biofuels. Nitrogen losses to surface waters are of great concern on both national and regional scales, and nitrogen losses from drained cropland in the Midwest have been identified as one of the major sources of N in streams. With the growing demand for biofuels and potentially increased corn production, measures are needed to allow the continued high agricultural productivity of naturally poorly drained soils in the Midwest while reducing N losses to surface waters. Therefore, the objective of this study is to examine the long-term effects of drainage system management on reducing N losses. To achieve the overall objective of this study, the USDA Annualized AGricultural Non-Point Source (AnnAGNPS) pollutant loading model was applied to the Ohio Upper Auglaize watershed located in the southern portion of the Maumee River Basin. In this study, AnnAGNPS model was calibrated using USGS monitored data; and then the effects of various subsurface drainage management practices on nitrogen loadings were assessed. Wider drain spacings and shallower depths to drain can be used to reduce nitrogen loadings. Nitrogen loading was reduced by 35% by changing drain spacing from 12 to 15 m (40 to 50 ft); and 15% nitrogen was reduced by changing the drain depth from 1.2 to 1.1 m (48 to 42 in.) and an additional 20% was reduced by changing the drain depth from 1.1 to 0.9 m (42 to 36 in.). In addition, nitrogen loadings could be significantly reduced by plugging subsurface drains from 1 November to 1 April of each year. About 64% nitrogen was reduced by completely controlling subsurface drainages for a drainage system with drain space of 12 m (40 ft) and drain depth of 1.2 m (48 in.).