Ammonia volatilization and yield response from urea applied to wheat with urease (NBPT) and nitrification (DCD) inhibitors

The urease inhibitor NBPT and the nitrification inhibitor DCD were examined in 2-year field study to evaluate their effects on ammonia volatilization from urea and on winter wheat productivity. Rain, plant canopy, temperature s and CEC of soils restricted total NH, volatilization from urea to 3-7% of the applied N. NBPT significantly decreased ammonia volatilization; the re duction was 42%-55% of losses with urea. NBPT+DCD seems to increase ammonia losses compared to NBPT alone. There were no significant effects of inhibi tors on grain yield. Only in one experiment. with the highest crop response to N application. NBPT and NBPT+DCD increased yield by 4% to 11%, compared to urea-untreated plots. Even though inhibitors perform well in reducing N H, losses, a yield response to their application might he expected only whe n the crop can respond to the N conserved by the inhibitors.