Multi-cropping with mixed vetch enhances wheat productivity and mitigates net greenhouse gas emissions by improving soil quality under reduced nitrogen fertilization

Promoting sustainable agricultural systems through improved cropping practices is central to the green transformation of agriculture. Incorporating green manure into multi-cropping systems partially substitutes chemical nitrogen (N) fertilizers without compromising grain yield, although it may increase greenhouse gas (GHG) emissions. However, it remains unclear whether mixed vetch could simultaneously increase wheat yield and mitigate net GHG emissions under reduced synthetic N inputs by improving soil carbon (C) and N pools, enzymatic activities, and specific microbial communities. A four-year (2019–2022) field trial was established in an arid irrigated area of northwest China. Treatments included four cropping systems: mixed common and hairy vetches (HCV), common vetch monoculture (CV), rapeseed monoculture (R), and fallow (F), combined with three chemical N rates: N3 (local traditional rate), N2 (20% N decrease), and N1 (40% N decrease). Without green manure, chemical N reduction decreased crop productivity, GHG emissions, and soil quality. Green manure, particularly HCV, increased wheat productivity, improved soil quality, and mitigated net GHG emissions, outperforming monoculture green manure and fallow practices. Relative to FN3, HCVN2 increased grain yield, grain protein content, net income, and energy use efficiency by 23.0%, 11.3%, 5.4%, and 19.1%, respectively. Although HCVN2 increased soil carbon dioxide (CO 2 ) emissions by 18.7%, it reduced nitrous oxide (N 2 O) and net GHG emissions by 14.5% and 39.8%, respectively, compared with FN3, by improving soil physicochemical conditions and C sequestration rate. Furthermore, HCVN2 enhanced soil dissolved and microbial biomass C and N pools, and stimulated sucrase, cellulase, and urease activities while decreasing nitrite reductase activity. Comprehensive evaluation using Entropy-TOPSIS, LWA, and NLWA methods confirmed HCVN2 as an effective agronomic strategy. These biochemical shifts were accompanied by an optimized bacterial community composition. Random forest analysis indicated that while enriched soil C and N pools are the primary drivers of wheat productivity and soil quality, the mitigation of GHG emissions is predominantly driven by decreased relative abundances of Gemmatimonadota and Nitrospirota . PLS-PM analysis showed that the bacterial community was positively linked to GHG emissions, which in turn exerted a direct negative effect on the comprehensive evaluation index. In arid irrigation areas, integrating mixed vetch with a 20% N reduction enhanced wheat productivity and mitigated net GHG emissions by improving soil quality, thereby promoting agricultural sustainability. This study provides a robust scientific foundation and operational guidance for establishing sustainable wheat production and environmentally beneficial, vetch-based diversified cropping strategies.