Polymer-Coated Urea Rates, Timings, and Ratio Combinations with Non-Coated Urea for Corn Production.

Efficient nitrogen (N) management through proper fertilizer selection, application rates, and timings is important factor for successful, sustainable and profitable corn (Zea mays L.) grain production systems. Use of enhanced efficiency fertilizers, such as polymer-coated urea (PCU), should target optimal rates, timings and ratios of readily available and controlled release of nitrogen (N) in order to maximize corn yields. Field research evaluated the effect of N application timing (pre-emergence or topdress), rates (0, 84, 126 and 168 kg N/ha), and ratios (100:0, 75:25, 50:50, 25:75, and 0:100) of PCU with non-coated urea (NCU) on grain yield, quality and N use efficiency during four years in Missouri. The experiment was 3-factor randomized complete block design with five replicates. Although top dressing of both PCU and NCU caused slight leaf injury 7 days after application (DAA), plants recovered 14 DAA with no effect on grain yield. Chlorophyll content of ear leaves increased with increasing rates of N and was higher in topdressed compared to pre-emergence applied N for corn in all years. Grain yield and protein concentration increased with increasing rate of N for both topdressed and pre-emergence applied treatments in all years. The topdressed treatments produced more grain yield with higher grain protein concentration than pre-emergence applied treatments in most years. The N use efficiency measured in terms of corn N uptake and grain apparent recovery efficiency was higher from topdressed than pre-emergence applied N. The results indicate that use of PCU over NCU and top dressing over a pre-emergence N application was beneficial for corn grain production in the region.