Late Application Nitrogen on Corn: Yield and Nutrient Losses in Southern Illinois.

In corn, typical nitrogen fertilization occurs either before planting or after crop emergence as late as the V6 stage. Since the majority of nitrogen uptake does not occur until V10 through R1, delaying nitrogen fertilization until V10 may reduce potential for early season soil N transformations and losses, while sustaining crop yields. A two year study, conducted across three southern Illinois locations, evaluated the effects of various late side-dress nitrogen applications and enhanced efficiency fertilizers on corn yield and residual mineral soil N. The various nitrogen treatments compared: rates from 0-224 kg N ha^-1; sources of urea and 32% UAN, with and without urease inhibitors NBPT (Agrotain® Ultra) and NBPT+NPPT (Limus®), and polymer-coated urea (ESN®); application timings at planting V6, V10, until VT; placement either dribble applied, broadcasted, or injected. Across sites and years, late (V10) nitrogen split applications generally resulted in corn yields greater than or equal to the same total nitrogen rate applied at planting. Most late N treatment differences varied between sites and years, but 56 kg N ha^-1 as broadcasted UAN at planting with 112 kg N ha^-1 as broadcasted urea, either with or without Agrotain® Ultra or Limus®, at V10 were on average highest yielding treatments among sites in both years, with 16% greater yield than 168 kg N ha^-1 as broadcasted UAN at planting. Urease inhibitors did not enhance yield in most instances, likely due to sufficient incorporating rainfall shortly after application. High amounts of residual mineral nitrogen were not found between 0-30 cm after harvest in the late nitrogen treatments.