Co-utilization of green manure and biochar with 30 % nitrogen reduction improves soil quality and mitigates carbon footprint

Green manure, also known as cover crops, is a clean source of organic manure. Partial substitution of N fertilizer with green manure provides a sustainable field management approach for alleviating soil degradation and global warming. However, whether biochar can enhance the environmental benefits of green manure remains unclear. To address this, a 2-year field trial was conducted with four treatments: monoculture maize with conventional N (N100) or 70% conventional N (N70), maize intercropping with green manure (i.e., common vetch) with 70% conventional N (GN70), and GN70 combined maize straw biochar (GN70M). Compared with N100, GN70 maintained maize yield, shoot dry weight, and N uptake. Notably, GN70M increased maize shoot dry weight and N uptake by 11.3% and 15.2% compared to N100, and by 11.0% and 9.1% compared to GN70, respectively. GN70M enhanced soil SOM, NO 3 – -N, and MBC, resulting in a 29.2% and 40.3% increase in soil quality index relative to N100 and GN70, respectively. Cumulative CO 2 emission and global warming potential (GWP) in GN70 were 26.3% and 24.4% lower than N100. GN70M further decreased cumulative CO 2 , N 2 O emissions, and GWP by 36.3%, 41.7%, and 36.9% compared to N100, and reduced soil cumulative N 2 O emissions by 35.1% compared to GN70. GN70 enhanced ecosystem C budget (NECB) by 4386 kg C ha –1 yr –1 and reduced C footprint (CF) by 17994 kg CO 2 -eq ha –1 yr –1 compared with N100. Relative to N100 and GN70, GN70M enhanced NECB by 6910 kg C ha –1 yr –1 and 2523 kg C ha –1 yr –1 , while decreasing CF by 30379 kg CO 2 -eq ha –1 yr –1 and 12369 kg CO 2 -eq ha –1 yr –1 , respectively. Moreover, GN70M increased net ecosystem economic benefit by 2518 CNY ha -1 yr –1 compared to N100. In conclusion, co-utilization of green manure and biochar with 30% N reduction enhanced soil quality and offered environmental benefits while maintaining maize high-yield, providing a novel insight for eco-efficient maize production. • Biochar enhanced the soil quality index when green manure substituted 30% chemical N • Substituting 30% of chemical N with green manure increased the net ecosystem C budget • Co-utilization of green manure and biochar brought the lowest C footprint • Green manure offset reduced net ecosystem economic benefits from lower chemical N