Agricultural Water Management 129 (2013) 21–30 Contents lists available at ScienceDirect Agricultural Water Management j ourna l h omepage: www.elsevier.com/locate/agwat Comparison of the performances of DRAINMOD-NII and ADAPT models in simulating nitrate losses from subsurface drainage systems Srinivasulu Ale a,∗ , Prasanna H. Gowda b , David J. Mulla c , Daniel N. Moriasi d , Mohamed A. Youssef e a Texas A&M AgriLife Research and Extension Center (Texas A&M University System), PO Box 1658, Vernon, TX 76385, USA b USDA-ARS Conservation and Production Research Laboratory, 2300 Experiment Station Road, Bushland, TX 79012, USA c Department of Soil, Water and Climate, University of Minnesota, 1991 Upper Bufold Circle, St. Paul, MN 55108, USA d USDA-ARS Grazinglands Research Laboratory, 7207 W Cheyenne Street, El Reno, OK 73036, USA e Department of Biological and Agricultural Engineering, North Carolina State University, 185 Weaver Labs, Raleigh, NC 27695, USA a r t i c l e i n f o Article history: Received 6 March 2013 Accepted 9 July 2013 Available online 7 August 2013 Keywords: DRAINMOD Hydrology Nitrate losses Tile drainage Water quality a b s t r a c t Adequate knowledge on the movement of nitrate-nitrogen (NO 3 -N) under different subsurface (tile) drain configurations and management practices in the U.S. Midwest is essential for developing reme- dial measures for reducing hypoxic conditions in the Gulf of Mexico. In this study, DRAINMOD-NII, a daily time-step soil carbon (C) and N model, was calibrated and validated for subsurface drainage and associated NO 3 -N losses, and crop yield. Long term (1983–1996) monitoring data measured on three experimental plots under continuous corn (Zea mays L.) with conventional tillage practice at the Uni- versity of Minnesota’s Southern Research and Outreach Center near Waseca, southern Minnesota was used for this purpose. Nash-Sutcliffe efficiency (NSE), Percent Error (PE) and Index of agreement (d) were used for assessing the model performance. DRAINMOD-NII predicted monthly subsurface drainage matched well with measured data during calibration (NSE = 0.81, PE = -7.8% and d = 0.94) and validation (NSE = 0.67, PE = -0.7% and d = 0.88) periods. Performance of DRAINMOD-NII for predicting monthly NO 3 - N losses in subsurface drainage was also good for both calibration (NSE = 0.64, PE = 0.8%, and d = 0.85) and validation (NSE = 0.62, PE = -5.3%, and d = 0.83) periods. DRAINMOD-NII predicted average (1983–1992) annual corn relative yield (93%), a ratio of crop yield in a year to the long-term average crop yield, was close to the observed relative yield (92.5%). DRAINMOD-NII simulation results were also compared and contrasted with those obtained by the Agricultural Drainage and Pesticide Transport (ADAPT) model with the same dataset. Both models performed equally well in predicting monthly subsurface drainage. However, DRAINMOD-NII performed slightly better in predicting monthly NO 3 -N losses and annual N budget, in addition to showing potential to simulate the effects of excess and deficit water stresses on crop yield. Studies comparing performances of different drainage models in the U.S. Midwest are useful to select an appropriate model for devising various strategies for reducing NO 3 -N losses from subsurface drainage systems, and thereby minimizing hypoxic conditions in the Gulf of Mexico. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Hypoxia in the Gulf of Mexico is a serious environmental issue that has been attributed primarily to nitrogen (N)-enriched waters from the Mississippi River entering the Gulf (Smith et al., 2006; Turner et al., 2005; Scavia et al., 2004; Turner and Rabalais, 2003; Rabalais et al., 2001; Mitch et al., 2001, 1999). The Upper Mississippi River Basin (UMRB) contributes a disproportionate one-third of the total nitrate-N (NO 3 -N) loading to the Mississippi River while its ∗ Corresponding author. Tel.: +1 940 552 9941x232; fax: +1 940 552 2317. E-mail addresses: sriniale@ag.tamu.edu, Srinivasulu.Ale@gmail.com (S. Ale). area accounts for only 15% of the total Basin area (Gowda et al., 2007; Gassman et al., 2006). These disproportionately high NO 3 - N loadings from the UMRB are associated with artificially drained cropland in the U.S. Midwest, particularly in the states of Illinois, Iowa, and Minnesota. More than 30% of the cropland in the U.S. Midwest has sub- surface drainage systems (Zucker and Brown, 1998). Subsurface drainage is a commonly used agricultural practice to enhance crop yield in naturally poorly drained, but highly productive soils. It provides trafficable conditions for field operations, improves soil aeration and microbial activity, and enhances crop productivity (Cannell, 1979; Keller et al., 2006). It also reduces crop diseases, soil erosion, and surface runoff (Fausey et al., 1986). However, 0378-3774/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.agwat.2013.07.008