How does biochar aging affect NH₃ volatilization and GHGs emissions from agricultural soils?

Biochar has been considered as a potential tool to mitigate soil ammonia (NH₃) volatilization and greenhouse gases (GHGs) emissions in recent years. However, the aging effect of biochar on soils remains elusive, which introduces uncertainty on the effectiveness of biochar to mitigate global warming in a long term. Here, a meta-analysis of 22 published works of literature with 217 observations was conducted to systematically explore the aging effect of biochar on soil NH₃ and GHGs emissions. The results show that, in comparison with the fresh biochar, the aging makes biochar more effective to decrease soil NH₃ volatilization by 7% and less risk to contribute CH₄ emissions by 11%. However, the mitigation effect of biochar on soil N₂O emissions is decreased by 15% due to aging. Additionally, aging leads to a promotion effect on soil CO₂ emissions by 25% than fresh biochar. Our findings suggest that along with aging, particularly the effect of artificial aging, biochar could further benefit the alleviation of soil NH₃ volatilization, whereas its potential role to mitigate global warming may decrease. This study provides a systematic assessment of the aging effect of biochar to mitigate soil NH₃ and GHGs, which can provide a scientific basis for the sustainable green development of biochar application.