The Use of Urease and Nitrification Inhibitors in Mitigating Direct and Indirect Greenhouse Gas Emissions from Australian Agriculture.

Intensive agricultural production, such as dairy pasture and vegetable systems, generally involve high nitrogen (N) inputs. However the efficiency of N utilisation becomes progressively lower as inputs increase. This can lead to substantial N loss to the environment under these high input systems. Urease and nitrification inhibitors, designed to slow urea hydrolysis and nitrification respectively, can be used to target losses from applied N. However, as each targets a different loss pathway (ammonia (NH₃) for urease inhibitors, nitrate leaching and nitrous oxide (N₂O) for nitrification inhibitors), the effects of urease and nitrification inhibitors on both NH₃ and N₂O will be different. Little is currently known about the impact of the inhibitors on emissions from manure and fertilizer applied to these intensive agricultural systems in Australia. We conducted a series of field experiments in pasture (temperature and subtropical) and temperate vegetable systems in Australia to address this knowledge gap. The effects of the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBPT) and the nitrification inhibitor 3,4-dimethyl pyrazole phosphate (DMPP) on the fluxes of NH₃ and N₂O varied with climate region and production systems. In general, NH₃ and N₂O emissions were decreased by the application of nBPT and DMPP, respectively, by 40–56% and 15–72%. However, an increase in NH₃ (as high as 20%) was observed upon DMPP application in a sandy and slightly alkaline vegetable soil. The results indicate that urease and nitrification inhibitors have the potential to reduce gaseous N loss from intensive agricultural systems, but it is important to consider different loss pathways when developing a strategy for reducing N loss.