Groundwater contamination from NO 3 -N leaching in corn (Zea mays L.) production with coarse-textured soils poses an environmental concern. Our objectives were to evaluate NO 3 -N leaching in continuous corn (CC), corn after soybean (Glycine max L.) (CSb), and soybean after corn (SbC) in irrigated sandy soils in Minnesota related to (i) N rate using best management practices of split-N application, (ii) a split-N application and single preplant applications of enhanced-efficiency fertilizers (EEF), and (iii) residual N treatment in SbC. Urea (0-315 kg N ha -1 in 45-kg increments) was broadcast as a split application (half at preplant and half at the V4 development stage) and polymer-coated urea (ESN), ESN/urea, and SuperU at preplant at a rate of 180 kg N ha -1 on an Arvilla sandy loam soil. In May and June, 75% of the total drainage and 73% of the total NO 3 -N leached occurred. At the economic optimum N rate (EONR), season-long NO 3 -N leaching rates were 86 and 106 kg NO 3 -N ha -1 for CC and CSb, respectively. In CC, reducing the EONR by 20% reduced grain yield by 4% and NO 3 -N leached by 9%, and a 25% reduction in EONR resulted in an additional 2% reduction for both, whereas no significant reductions occurred for CSb. Similar NO 3 -N leaching occurred with EEFs and the split-N application. After 4 yr of no N application, we measured 9 to 20 mg NO 3 -N L -1 and leaching of 21 to 51 kg NO 3 -N ha -1 , highlighting the difficulty of meeting drinking water quality standards in corn cropping systems.
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