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.Core Ideas In irrigated sandy soils, applying high rates of N needed for economic optimum yield is best accomplished by splitting the application. Canopy sensors and basal stalk nitrate‐N generally under estimated N rate needed to optimize grain yield. Enhanced efficiency fertilizers applied at pre‐plant are not as effective as split applications of urea in irrigated sandy soils.
Groundwater contamination from NO-N leaching in corn ( L.) production with coarse-textured soils poses an environmental concern. Our objectives were to evaluate NO-N leaching in continuous corn (CC), corn after soybean ( 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 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 on an Arvilla sandy loam soil. In May and June, 75% of the total drainage and 73% of the total NO-N leached occurred. At the economic optimum N rate (EONR), season-long NO-N leaching rates were 86 and 106 kg NO-N ha for CC and CSb, respectively. In CC, reducing the EONR by 20% reduced grain yield by 4% and NO-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-N leaching occurred with EEFs and the split-N application. After 4 yr of no N application, we measured 9 to 20 mg NO-N L and leaching of 21 to 51 kg NO-N ha, highlighting the difficulty of meeting drinking water quality standards in corn cropping systems.
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