Potential relationships between greenhouse gas emissions and soil physicochemical properties in summer maize field with straw-biochar amendment

Agriculture accounts for approximately 34 % of global greenhouse gas (GHG) emissions, while intensive farming practices are associated with soil fertility depletion, creating persistent challenges for food security and climate goals. Soil-based solutions, including crop residue return and biochar amendments, have been proposed to enhance fertility and carbon retention, yet reported effects on GHG fluxes remain variable across soil types and microbial dynamics. Field-level evidence of straw-biochar co-application outcomes remain limited. A four-year field experiment in maize systems compared straw removal (CK), straw return (SR), biochar amendment (BC), and straw-biochar co-application (CA). Measurements included soil physicochemical properties, microbial biomass, and GHG fluxes (CO 2 , N 2 O, and CH 4 ). Relative to CK, SR and BC were associated with higher soil water content, organic carbon, nitrogen pools, dissolved organic nutrients, and microbial biomass. Compared with SR, CA reduced mineral nitrogen, dissolved organic nutrients, and microbial biomass, with significant reductions in cumulative CO 2 (11.1 %) and N 2 O (31.5 %), alongside higher CH 4 uptake. Partial least squares path analysis indicated that straw-biochar management accounted for 64.4 % of CO 2 , 66.6 % of N 2 O, and 17.8 % of CH 4 variation through associations with soil properties. Soil CO 2 and N 2 O fluxes were mainly driven by dissolved organic carbon, dissolved organic nitrogen, and microbial biomass nitrogen, showing positive correlations ( p < 0.05). These results suggest that straw-biochar co-application can contribute to soil fertility while reducing emissions, though trade-offs in nutrient availability remain. The regional context, single biochar type, and limited timeframe provide opportunities for improvement through multi-site, long-term, and multi-feedstock studies that incorporate microbial and isotopic analyses. Overall, the findings provide field-level evidence that integrated residue management may support soil carbon sequestration, climate mitigation, and sustainable intensification in high-throughput, low-carbon agri-food systems. • SR and BC increased CO 2 and N 2 O emissions, while reduced CH 4 uptake compared to CK. • Biochar significantly mitigated straw return induced greenhouse gas emission peaks. • CA decreased cumulative CO 2 and N 2 O emissions by 15.3 % and 25.8 % relative to SR. • DOC, DON, and MBN had significant positive relationships with CO 2 and N 2 O emissions. • Soil physicochemical properties explained 64.4 % of CO 2 and 66.6 % of N 2 O fluxes.