Urease inhibitors reduced ammonia emissions from cattle urine applied to pasture soil

Two field experiments were conducted to compare the effectiveness and longevity of urease inhibitor (UI), N-(2-Nitrophenyl) phosphoric triamide (2-NPT) with commonly used UI N-(n-butyl) thiophosphoric triamide (nBTPT) in reducing ammonia (NH3) emissions from cattle urine applied to pasture soil at different periods during summer and autumn. Higher proportion of applied urine N (15–24%) was emitted as NH3–N in the summer than in autumn (only 5%). In the summer experiment, only 2-NPT significantly reduced total NH3 emissions (20% reduction), only when urine was applied 28 days after the inhibitor application. In autumn, both inhibitors significantly reduced emissions from urine applied either 3 h before or immediately before inhibitor application. However, the reduction was greater from urine applied immediately before inhibitor application (52–73% reduction) compared to 3 h before inhibitor application (35–41% reduction). The emissions reduction from urine applied immediately before inhibitor application was greater with 2-NPT (73% reduction) compared to nBTPT (52% reduction). Overall, 2-NPT showed a greater effectiveness and longevity at reducing NH3 emissions compared to nBTPT. Although, the total amount of N preserved by using 2-NPT is relatively small, compared to the total N added as urine, its use can contribute to mitigating a component of a farm’s deleterious environmental emissions. There was no effect of inhibitors on pasture dry matter yield and N uptake in both experiments.