Objectives This study aimed to elucidate the effects of planting green manure after wheat harvest and returning green manure before wheat sowing on soil physicochemical properties, microbial community structure, and ecological functions.

Methods A long-term positioning experiment of multiple cropping green manure after wheat harvest was established in 2009 in Wuwei, Gansu Province, using common vetch (Vicia sativa L.) as the test green manure. Five treatments were set up: no fertilization and no green manure control (CK); multiple cropping green manure only (GCF₀); 100% nitrogen(N) and phosphorus(P) chemical fertilizers only (CF₁₀₀); multiple cropping green manure and 100% NP chemical fertilizers (GCF₁₀₀); multiple cropping green manure and 30% reduction of NP chemical fertilizers (GCF₇₀). In June 2024, after wheat harvest, soil samples were collected from the 0-20 cm layer to analyze soil physicochemical properties, microbial community diversity, and ecological functions.

Results Compared with CK, long-term multiple cropping and returning of green manure treatments (GCF₀, GCF₁₀₀, GCF₇₀) significantly increased soil water holding capacity and porosity, decreased bulk density. GCF₁₀₀ treatment also demonstrated higher water holding capacity and porosity, and lower bulk density than CF₁₀₀. However, no significant differences were observed among among the three multiple cropping green manure treatments. The three multiple cropping green manure treatments also demonstrated comparable but significantly higher soil organic carbon content than CF₁₀₀ treatment. Multiple cropping green manure treatments significantly increased soil total and available nitrogen contents,relative to CK and CF₁₀₀ treatments. In contrast, soil phosphorus content decreased with reduced chemical fertilizer application. Compared to CF₁₀₀, GCF100 significantly decreased the Shannon index of soil bacteria, increased the Simpson index, and resulted in an increased relative abundance of Bacteroidotaand a significant decrease in Chloroflexiabundance. PICRUSt2 functional prediction indicated that multiple cropping green manure treatments enhanced carbohydrate and amino acid metabolism, while no multiple cropping green manure treatments exhibited higher cofactor and vitamin metabolism capabilities. Redundancy analysis revealed that soil organic carbon, total nitrogen, and available nitrogen were the main factors influencing soil microbial community structure.

Conclusions In the Hexi irrigation area, long-term multiple cropping with incorporation of common vetch green manure significantly increased soil organic carbon content, improved soil physical properties, and enhanced soil nutrient content and availability, particularly nitrogen. Compared with increased chemical fertilizer application, green manure incorporation was more effective in improving soil nitrogen content. Meanwhile, long-term green manure incorporation enhanced the carbohydrate and amino acid metabolic capacities of soil bacteria. In summary, the potential ecological functions conferred by green manure incorporation offer an effective approach for achieving green and sustainable agricultural development in the Hexi region.