Biochar Outperforms Straw and Manure at Equal Carbon Inputs for Mitigating Greenhouse Gas Emissions and Enhancing Soil Health in Rice Paddies

Achieving carbon neutrality in rice cultivation requires optimising organic amendments to simultaneously enhance productivity, soil health, and reduce greenhouse gas (GHG) emissions. While straw, biochar, and manure effects have been studied individually, their comparative efficacy under equivalent carbon inputs remains unclear. We conducted a flooded paddy field experiment with four treatments: control (no amendment), air‐dried rice straw, fermented pig manure, and pyrolysis biochar, each applied once at an equal carbon input of 1200 kg C ha −1 . Over one rice season, we measured CH 4 and N 2 O fluxes and cumulative emissions, calculated GWP, and determined rice yield and agronomic traits. Soil properties (SOC, DOC, pH, and available nutrients) and microbial diversity were assessed, and a comprehensive soil health index (SHI) was computed. Biochar application significantly reduced cumulative CH 4 and N 2 O emissions, lowering the global warming potential (GWP) by 31.35%. Conversely, manure increased CH 4 emissions by 41.01% and GWP by 26.94%. Biochar induced the greatest SHI improvement (+10.97 units) by enhancing SOC and DOC. Manure significantly boosted rice yield (155.7%) due to higher nutrient loading, while biochar and straw improved key agronomic traits but had limited yield effects. In general, biochar application offers the most favourable trade‐off by significantly mitigating GHG emissions and enhancing soil health, positioning it as a strategic solution for sustainable rice cultivation towards carbon neutrality.