Meta-analysis of direct nitrous oxide emissions and ammonia volatilization from irrigated wheat in calcareous soils under semi-arid conditions

Nitrous oxide (N2O) is the most important stratospheric ozone-depleting gas of the 21st century. Most N2O emissions occur in soils and are associated with agricultural activities. Ammonia (NH3) is not a greenhouse gas, but it can indirectly contribute to greenhouse gas emissions. NH3 volatilization is an important indirect N2O emission pathway in agricultural systems. In addition, NH3 can have significant effects on both human health and the natural environment, and its emissions negatively affect biodiversity. A meta-analysis was conducted to evaluate NH3 and N2O losses and the effectiveness of adding urease and nitrification inhibitors on direct N2O emissions and NH3 volatilization. Data were used from 14 separate studies that simultaneously investigated direct N2O emissions and NH3 volatilization from irrigated wheat. All studies were conducted on irrigated wheat in semi-arid climates and on calcareous soils with urea application. The average direct N₂O emission factor for irrigated wheat was 0.4%. Our results showed that, on average, nitrification inhibitors reduced direct N2O emissions by 35% and increased NH3 volatilization by 29%. The average NH3 emission factor was 32% and urease inhibitors reduced NH3 volatilization by 41%. The results showed that indirect N2O emissions from NH3 volatilization should be considered in these conditions.