Using urease and nitrification inhibitors to decrease ammonia and nitrous oxide emissions and improve productivity in a subtropical pasture.

Urease and nitrification inhibitors are designed to mitigate ammonia (NH3) volatilization and nitrous oxide (N2O) emission, but uncertainties on the agronomic and economic benefits of these inhibitors prevent their widespread adoption in pasture systems, particularly in subtropical regions where no such information is available. Here we report a field experiment that was conducted in a subtropical pasture in Queensland, Australia to examine whether the use of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT, applied as Green UreaNV®) and the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP, applied as Urea with ENTEC®) is environmentally, agronomically and economically viable. We found that Green UreaNV® and Urea with ENTEC® decreased NH3 volatilization and N2O emission by 44 and 15%, respectively, compared to granular urea. Pasture biomass and nitrogen (N) uptake were increased by 22-36% and 23-32%, respectively, with application of the inhibitors compared to granular urea. A simple economic assessment indicates that the fertilizer cost for pasture production was 5.4, 4.4 and 6.0 Australian cents per kg dry matter for urea, Green UreaNV® and Urea with ENTEC®, respectively, during the experimental period. The mitigation of N loss using the inhibitors can reduce the environmental cost associated with pasture production. These results suggest that the use of these inhibitors can provide environmental, agronomic and economic benefits to a subtropical pasture.