Extreme climate weakens the effect of biochar in increasing yield and reducing N2O emissions

Context: Climate change and cropland degradation threaten global food security and greenhouse gas mitigation. Applying biochar has been promoted as a solution to sustain crop yields, reduce nitrous oxide (N2O) emissions, and improve soil quality. Objective and methods: However, the long-term patterns of these effects of biochar remain uncertain and may be affected by extreme climatic events. In this 12-year field experiment with different doses of biochar retention, effect size analysis, comprehensive soil health assessment, and structural equation modeling were used to evaluate biochar's temporal effects on productivity, N2O emissions, and their relationship with soil environment and aboveground climate. Results: Biochar provided positive impacts, increasing wheat yield by 6.2 %, reducing N2O emissions by 6.0 %, and improving the soil health index by 9.5 %. Biochar significantly increased soil temperature and moisture in most years. Notably, biochar's effects on yield and N2O emissions fluctuated nonlinearly over time. Extreme climate indices had the largest negative effect on yield, while soil properties offered the greatest positive effect. The extreme climate index had the largest positive correlation with the N2O emission effect. Conclusion: Extreme climate events are not conducive to the benefits of biochar in increasing production and reducing N2O emissions. Growing season climate factors (temperature and precipitation) indirectly enhance the yield-increasing effect of biochar, while growing season precipitation indirectly weakens the effect of biochar in reducing N2O emissions. Implications: Our work offers a model for sustainable food production, emphasizing the role of biochar in boosting long-term productivity, soil health, and environmental sustainability. However, the resilience of biochar to extreme climate events needs to be viewed with caution. The results provide new insights into the application of biochar for maintaining yield stability and food security under climate change.