Applied Engineering in Agriculture Vol. 27(3): 335‐344 E 2011 American Society of Agricultural and Biological Engineers ISSN 0883-8542 335 ASSESSMENT OF SUBSURFACE DRAINAGE MANAGEMENT PRACTICES TO REDUCE NITROGEN LOADINGS USING ANNAGNPS Y. Yuan, R. L. Bingner, M. A. Locke, F. D. Theurer, J. Stafford ABSTRACT. 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.). Keywords. AnnAGNPS watershed modeling, Ohio Upper Auglaize watershed, Midwest, Drainage management practices, Water quality. he Future Midwest Landscape (FML) study is part of the U.S. Environmental Protection Agency's (EPA) new Ecosystem Services Research Program, undertaken to examine the variety of ways in which landscapes that include crop lands, conservation areas, wetlands, lakes, and streams affect human well‐being. The Submitted for review in April 2010 as manuscript number SW 8520; approved for publication by the Soil & Water Division of ASABE in January 2011. Although this work was reviewed by USEPA and approved for publication, it may not necessarily reflect official Agency policy. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. The authors are Yongping Yuan, ASABE Member Engineer, Research Hydrologist, USEPA‐Office of Research and Development, NERL‐ESD‐Landscape Ecology Branch, Las Vegas, Nevada; Ronald L. Bingner, Agricultural Engineer, USDA‐ARS Watershed Physical Processes and Water Quality and Ecology Research Unit, National Sedimentation Laboratory, Oxford, Mississippi; Martin A. Locke, ASABE Member Engineer, Research Leader, USDA‐ARS Water Quality and Ecology Research Unit, National Sedimentation Laboratory, Oxford, Mississippi; Fred D. Theurer, ASABE Member Engineer, Agricultural Engineer, USDA‐NRCS‐National Water and Climate Center, Beltsville, Maryland; and Jim Stafford, Ohio State CEAP Coordinator, USDA‐NRCS Columbus, Ohio. Corresponding author: Yongping Yuan, USEPA‐Office of Research and Development, NERL‐ESD‐Landscape Ecology Branch, P.O. Box 93478, 944 East Harmon Avenue, Las Vegas, NE 89119; phone: 702‐798‐2112; e‐mail: yuan.yongping@epa.gov. goal of the FML is to quantify current and future landscape services across the 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 (increased corn production particularly). Nitrogen (N) losses to surface waters are of great concern on both national and regional scales. Scientists have concluded that large areas of hypoxia in the northern Gulf of Mexico are due to excessive nutrients derived primarily from agricultural runoff via the Mississippi River (Rabalais et al., 1996, 1999; Aulenbach et al., 2007; USEPA Science Advisory Board, 2007). Excessive N and phosphorus loading is also responsible for algal blooms and associated water quality problems in lakes and rivers in other locations, such as the Lake Erie of the great lake systems in Northern Ohio (Ohio EPA, 2008). Loss of N to surface waters is also a problem on a local level. Excess nitrate in drinking water can be toxic to humans, and treatment is expensive when nitrate in surface water supplies exceed EPA threshold levels (USEPA, 2008). Nitrogen losses from drained cropland have been identified as one of the major sources of N in streams. There is strong evidence that artificial drainage, installed in many regions of the Midwest, improves crop production and increases N losses to surface waters (Gilliam et al., 1999; T