Late-Split Nitrogen Application on Corn.

Late-Split Nitrogen Application on Corn

Derek J. Rapp and Emerson D. Nafziger, University of Illinois

The practice of applying a last (or additional) increment of N fertilizer during late vegetative growth of corn using high-clearance equipment has grown rapidly in the last few years, despite the absence of evidence supporting the profitability of this practice. We established a set of trials in which a range of N rates from 0 to 280 kg/ha were applied as UAN solution, either all at planting or with 56 kg N reserved and hand-applied at the base of the plants at tasseling (late-split N). Averaged over four trials in 2016 in which corn followed soybean, the economically optimum N rate was 152 kg/ha for N applied at planting and 155 kg/ha for late-split N, and the grain yields at these N rates were 14.7 and 14.8 Mg/ha, respectively. Averaged over three trials in which corn followed corn, the optimum N rate was 170 kg/ha for both early and late-split N, and yield at the optimum N rate were 14.5 Mg/ha for both. While the 56 kg/ha of N applied late was taken up and produced additional yield (at the lower N rates), it did not increase the return to N; with higher application costs, late-split N was less profitable than application of all of the N at planting. It appears that late-split N should not be adopted as a routine practice on productive soils that here showed their capacity to supply the crop with N from fertilizer applied early in the season.