Suitable biochar application practices simultaneously alleviate N₂O and NH₃ emissions from arable soils: A...

Nitrogen (N) fertilization profoundly improves crop agronomic yield but triggers reactive N (Nr) loss into the environment. Nitrous (N₂O) and ammonia (NH₃) emissions are the main Nr species that affect climate change and eco-environmental health. Biochar is considered a promising soil amendment, and its efficacy on individual Nr gas emission reduction has been widely reported. However, the interactions and trade-offs between these two Nr species after biochar addition have not been comprehensively analysed. The influencing factors, such as biochar characteristics, environmental conditions, and management measures, remain uncertain. Therefore, 35 publications (145 paired observations) were selected for a meta-analysis to explore the simultaneous mitigation potential of biochar on N₂O and NH₃ emissions after its application on arable soil. The results showed that biochar application significantly reduced N₂O emission by 7.09% while having no significant effect on NH₃ volatilisation. Using biochar with a low pH, moderate BET, or pyrolyzed under moderate temperatures could jointly mitigate N₂O and NH₃ emissions. Additionally, applying biochar to soils with moderate soil organic carbon, high soil total nitrogen, or low cation exchange capacity showed similar responses. The machine-learning model suggested that biochar pH is a dominating moderator of its efficacy in mitigating N₂O and NH₃ emissions simultaneously. The findings of this study have major implications for biochar application management and aid the further realisation of the multifunctionality of biochar application in agriculture, which could boost agronomic production while lowering environmental costs.