Biochar-Based Fertilization Mitigates CH4 Emissions Without Yield Penalties by Regulating Soil Chemical and Microbial Processes in Paddy Fields

Mitigating methane (CH4) emissions from paddy fields without compromising yield remains a critical challenge for sustainable agriculture, primarily due to trade-offs between emission reduction and nutrient availability. Biochar-based fertilizer (BF), which integrates biochar with mineral nutrients, may address this constraint by regulating carbon and nitrogen availability. This study evaluated the effects of biochar-based fertilization on CH4 emissions and rice productivity. A one-season field experiment was conducted in Hydragric Anthrosols with four treatments: no fertilization (control), conventional chemical fertilization (CF), integrated application of biochar-based and chemical fertilizers (CBF), and biochar-based fertilizer alone (BF). Methane fluxes were monitored alongside soil physicochemical properties and the abundances of key functional microbial genes. Compared with CF, BF significantly reduced cumulative CH4 emissions by 23.24% while maintaining comparable rice yield, resulting in a 28.67% reduction in yield-scaled CH4 emissions. Biochar-based fertilization decreased dissolved organic carbon availability, buffered NH4+-N concentrations, and increased soil pH. These changes shifted the microbial balance of CH4 cycling, suppressing methanogenesis and enhancing methane oxidation, as reflected by a lower mcrA/pmoA ratio. Structural equation modeling indicated that CH4 mitigation was jointly driven by reduced methanogenic activity and enhanced methane oxidation. Overall, biochar-based fertilization regulates soil chemical and microbial processes to mitigate CH4 emissions without yield penalties, demonstrating strong potential as a scalable and field-applicable strategy for low-carbon rice production.