Mineral nitrogen input modulates the methane mitigation potential of biochar in rice systems: based on meta-analysis and field experiment demonstration

Abstract The application of organic materials has a profound impact on CH₄ emissions from paddy fields. Biochar has been reported to mitigate CH₄ emissions, but this conclusion has recently been challenged and requires further investigation. This study aimed to determine the effect of biochar on paddy CH₄ emissions by integrating organic amendment emission data through network meta-analysis (NMA), and to identify the key moderators using multiple meta-regression (MR) approaches. Field experiments were conducted to verify the conclusions of MR. Based on 146 entries from 51 studies, a mixed-effects meta-analysis was conducted to evaluate the effects of organic material applications on soil CH₄ emissions. We focused on the biochar mitigation potential in rice systems and validated the conclusions through a field experiment. Biochar demonstrated the lowest methane emissions among all treatments. Carbon to nitrogen ratio of biochar (MC:N) and mineral nitrogen input (ICN) were identified as key moderators influencing the methane mitigation potential of biochar in rice cultivation. ICN was the most influential factor. When ICN exceeded 291.18 kg ha −1 , biochar tended to increase methane emissions, whereas at lower ICN levels, it contributed to emission reductions. Field experiments confirmed that at high mineral N levels (310 kg ha −1 ), biochar significantly increased CH₄ flux and emission potential. Overall, this study highlights the potential of biochar to reduce methane emissions in rice systems and underscores the importance of regulating mineral nitrogen inputs to maximize its mitigation effectiveness. Graphical Abstract