Polymer-Coated Urea Application Timings, Nitrogen Rates, and Blending Ratios Affect Corn Production.

Degradation of Great Lakes Basin water quality in combination with increasingly unpredictable spring weather conditions have placed greater emphasis on identifying nitrogen (N) fertilizer strategies that more closely synchronize N availability with peak corn (Zea mays L.) N demand.  A field experiment was initiated in south-central Michigan to determine the N availability of both polymer-coated urea (PCU) and conventional urea at multiple application timings, N rates, and blending ratios in corn management programs involving one N application.  The study was arranged as a 3 (application timings of early pre-plant incorporated, at-plant incorporated, and sidedress surface application) x 2 (N fertilizer application rates of 84 and 168 kg N ha^-1) x 5 (PCU and urea blending ratios) factorial and a non-treated control.  Data collection included R1 chlorophyll measurements, leaf firing, stalk nitrate analysis, end-of-season total N analysis of vegetation and grain, and yield parameters.  Significant two-way interactions of N rate by blending ratio (leaf chlorophyll, leaf firing, and stalk nitrate) and application timing by blending ratio (yield) were present during the first year of study.  Early pre-plant incorporated applications containing 75% PCU provided greater yield for this application timing.  At planting time, blending ratios should shift towards increased percentages of urea to maximize corn yield.  Although sidedress PCU application may not synchronize N release and plant uptake, the urea polymer coating continued to function as a urease inhibitor resulting in greater yield response with PCU included in the sidedress blending ratio.  Polymer-coated urea has the potential to provide some degree of insurance against unpredictable weather conditions while maintaining or improving corn yield and could result in a win-win situation for both producers and environmental stewardship.