Nitrous oxide (N₂O) and nitric oxide (NO) are detrimental reactive gaseous oxides of nitrogen. Excessive application of nitrogen fertilizers in cropping systems has significantly increased the emissions of these gases, causing adverse environmental consequences. Previous studies have demonstrated that biochar amendment can regulate soil-N dynamics and mitigate N losses, but they lacked simultaneous assessments of soil N₂O and NO emissions. Thus, the factors influencing the emissions of nitrogen oxides are still unclear. Therefore, this study examined the impact of biochar application on simultaneous N₂O and NO emissions based on 18 peer-reviewed papers (119 paired observations). A machine learning model (boosted regression tree model) was adopted to assess the potential influencing factors, such as soil properties, biochar characteristics, and field management conditions. The addition of biochar reduced N₂O and NO emissions by 16.2% and 14.7%, respectively. Biochar with a high total carbon content and pH, from woody or herbaceous feedstock, pyrolyzed at a high temperature, applied at a moderate rate and to soil with a high-silt content, a moderate pH, and coarse texture, could simultaneously reduce soil N₂O and NO emissions. Biochar amendment, thus, has the potential to lower the environmental impact of crop production. Furthermore, the influence of soil properties, biochar characteristics, and field management should be considered in the future to enhance the efficacy of biochar.

Substantial ammonia (NH₃) losses from rice production result in poor nitrogen (N) use efficiency and environmental damage. A data synthesis using the published literature (127 studies with 700 paired observations), combined with an incubation experiment using 50 paddy soils from across China, were conducted to improve the current understanding of the NH₃ loss from paddy rice and its drivers. The efficacy of the urease inhibitor Limus^® for reducing NH₃ losses was also evaluated. The mean loss of N, through NH₃ volatilization, was 16.2% of the urea-N applied to paddy rice. The largest losses were from double rice cropping systems, and losses increased with the N application rate, surface application of N, unstable N types (ammonium bicarbonate and urea), and high floodwater pH. Under simulated flooded conditions, urea amended with Limus^® reduced NH₃ loss by 36.6%, compared to urea alone, but floodwater pH had a significant effect on inhibitor efficacy. Key driving factors were air temperature, N application rate, and floodwater pH. The effectiveness and limitations of the inhibitor in NH₃ emission mitigation was examined, as well as its basis as one means of N pollution control in paddy rice cropping systems.