Corn (Zea mays L.) in irrigated coarse-textured soils can be very productive with N applications, but excess N can increase groundwater contamination. Our objectives were to (i) determine the economic optimum nitrogen rate (EONR) for continuous corn (CC) and corn after soybean [Glycine max (L.) Merr.] (CSb), (ii) evaluate corn yield and nitrogen use efficiency (NUE) of split urea-N and single pre-plant application of enhanced-efficiency fertilizers, and (iii) determine the utility of canopy sensors and basal stalk nitrate-N test to manage N. Rotations of CC in Dakota County, Minnesota, and CC, CSb, and soybean after corn (SbC) in Pope County, Minnesota, were established in 2011 to 2014 with 0, 45, 90, 135, 180, 225, 270, and 315 kg urea-N ha–1 as split-application (half at pre-plant and half at V4), and pre-plant applications of SuperU (Koch Fertilizer LLC, Wichita, KS) at 180 kg N ha–1, ESN(Agrium Advanced Technologies, Loveland, CO)/urea blend 90/90 kg Nha–1, and ESN at 180 and 225 kg N ha–1. The EONR for CC was 233 kg N ha–1. The fertilizer replacement value in CSb was 56 kg N ha–1 and the EONR was 49 kg N ha–1 less than in CC. Canopy sensors and basal stalk nitrate-N generally under estimated N rate. A split-urea application increased corn grain yield by 5.4% (0.63 Mg ha–1), partial factor productivity (PFP) by 6% and agronomic efficiency (AE) by 12% relative to mean single pre-plant application of enhanced-efficiency fertilizers. In irrigated sandy soils, applying high rates of N needed for economic optimum yield is best accomplished by splitting the application.
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© 2016 by the American Society of Agronomy.