Engineered biochar effects on methane emissions and rice yield under alternate wetting and drying in paddy soils

Biochar is a promising strategy for improving crop yield and mitigating greenhouse gas emissions. However, the impacts of acid modified biochar on CH 4 emissions and yield in rice fields are not comprehensively understood, especially under alternate wetting and drying irrigation (I AWD ). Here, we conducted a 3-yr field experiment with two irrigation regimes (I CF : continuous flooding irrigation, I AWD ) and three biochar treatments (B 0 : no biochar; B 20 : 20 t ha -1 rice straw biochar; and B 20A : 20 t ha -1 acid modified rice straw biochar). Results showed I AWD reduced CH 4 emissions by 63-80% and water consumption by 10-12% but threatened the rice soil fertility. B 20 and B 20A increased soil cation exchange capacity by 13-36%, soil organic carbon by 24-44% and C/N by 17-36% over the three years. However, compared to B 0 , B 20 tended to increase CH 4 emissions and factor (CH 4EF ), reduced grain yield by 6% in 2019, but B 20A suppressed CH 4 emissions by 19% while maintaining a stable grain yield. B 20 and B 20A enhanced yield by 5% and 8%, 11% and 12% and decreased CH 4 emissions by 22% and 38%, 38% and 40% in 2020 and 2021, respectively. B 20A alleviated its initial negative impact on CH 4 emissions and yield in 2019 due to acid modified biochar enhancing more acidic and oxygenated functional groups. I AWD B 20A decreased CH 4 emissions by 75-89% and greenhouse gas emission intensity (GHGI) by 75-90% compared to I CF B 0 over the three years. Consequently, B 20A coupled with I AWD achieves sustainable use of water resources, improves soil degradation and mitigates climate change. • Yield is threatened by lower soil fertility under I AWD . • Biochar can improve soil fertility and yield, and reduce CH 4 emissions. • The initial incorporation of fresh biochar increase the risk of CH 4 emissions. • Acid modified biochar alleviates biochar initial yield decrease and CH 4 emissions.