Effects of Combined Stover and Biochar Return on Soil Organic Matter and Microbial Characteristics

China possesses abundant stover resources, and promoting the recycling of stover instead of open burning is a crucial measure for reducing carbon emissions and protecting the atmospheric environment. This study systematically investigated the effects of four stover management strategies—stover removal (CK), direct stover return (SD), stover biochar return (BC), and a combined half-stover half-biochar return (SB)—on soil physicochemical properties, enzyme activities, and microbial communities in the meadow brown soil of Northeast China. The results demonstrated that BC treatment significantly increased the soil total carbon (TC), total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), and available potassium (AK) contents. SB treatment showed the most pronounced enhancement in TP. Regarding enzyme activities, Compared with CK, SD significantly increased the activity of N-acetyl -β -D-glucosaminase (NAG). Furthermore, all stover return practices significantly enhanced bacterial community diversity but suppressed fungal diversity. SB treatment resulted in the greatest improvement in bacterial richness and diversity. Beta diversity analysis revealed that SD and SB significantly altered the soil microbial community structure, whereas BC had a minimal impact. In conclusion, the combined application of stover and biochar (SB) exhibited the most consistent and beneficial outcomes across multiple soil health indicators, highlighting its potential as an effective integrated strategy for enhancing soil fertility, promoting carbon sequestration, and sustaining the health of the meadow brown soil ecosystem in Northeast China.