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 21^st 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.