Mitigating Ammonia Volatilisation from Agricultural Systems—a Global Synthesis.

Ammonia (NH₃) volatilization is a significant pathway of nitrogen (N) loss from cropping systems. Quantifying NH₃ volatilization is often challenging and requires complex micrometeorological techniques. A number of studies have investigated the effects of management practices on NH₃ emission, but the findings are inconclusive. A meta-analysis was conducted to quantitatively synthesise the global literature on the strategies for mitigating NH₃ emission from agricultural systems. Unlike qualitative reviews, a meta-analysis combines results from different studies to identify patterns among study results. The mitigation strategies included in our meta-analysis were: N application method (deep placement), fertilizer type (ammonium-based vs. urea) irrigation, and the use of urease inhibitors and controlled release fertilizers. Irrigation after fertilization and deep placement of N fertilizers reduced NH₃ emission by around 42% and 70%, respectively. Ammonium-based fertilizers were effective in reducing NH₃ loss when compared to urea. Both urease inhibitors and controlled release fertilisers effectively decreased NH₃ volatilization by 55-69%, but the effects varied with the type of inhibitors or fertilizers. The findings provide critical information on how to minimize NH₃ volatilization and increase N use efficiency and productivity in cropping systems, nationally and internationally.