Effect of Urease Inhibitors on Corn Grain Yields and N Volatilization Losses.

Broadcast applications of nitrogen (N) fertilizers using sources with a high risk of losses represent a challenge for corn under continuous no-tillage. The objective of this study was to evaluate the effect of an additive (Agrotain™) mixed with urea in corn grain yield and N volatilization losses with different amounts of crop residue cover. The experiment was conducted in 2007 at INTA Rafaela Research Station, Santa Fe, Argentina. Ten treatments were applied using a split plot design, where the main plot was the amount of residue and the sub-plot was the fertilization treatment, randomly arranged in 4 replications. Fertilization treatments were a control, 70 and 140 kg N ha^-1 with and without additive. Soybean residue levels were 3 and 8 Mg ha^-1 of dry biomass. The use of additive increased the soil test NO₃-N (30-cm depth) at V6 corn growth stage between 3.1 and 6.6 mg kg^-1 for the high residue level, and between 3.4 and 4.5 mg kg^-1 for the low residue level. The use of additive significantly reduced the cumulative N volatilization losses from 13.7 to 3.6% with the low N rate and from 30.8 to 6.7% with the high N rate, at the low residue level. At the high residue level, the reduction was also significant, but smaller. Average grain yield response to N application was 1876 kg ha^-1 (7296 vs. 9172 kg ha^-1). The residue levels did not generate significant grain yield differences. The N rates increased grain yield by 1000 kg ha^-1 using urea and 1160, using urea + additive. The use of additive increased average grain yield of the 2 N rates and 2 residue levels by 631 kg ha^-1. Use of additives that reduce the N losses can contribute to increase the use efficiency and reduce negative environmental impacts.