To analyze the effects of in situ vegetable residue return on soil properties and microorganisms, this study conducted a continuous three-season in situ residue return experiment with four treatments: no return (CK), residue return (HTJ), residue return + compound microbial inoculant (HTJS), and residue return + ammonia water (HTJN). This study compared the treatment effects on soil quality. The results showed that, after the third tillage, the HTJS treatment increased soil organic carbon, total nitrogen, and mineralizable organic carbon content, and significantly enhanced the activity of soil β-glucosidase and soil peroxidase, which are related to carbon cycling enzymes compared to other treatments. There were no significant differences in bacterial or fungal α-diversity among treatments. Differences in fungal community soil β-diversity among treatments were significant. The HTJS treatment enriched organic matter-degrading bacteria Flavisolibacter and Devosia. Although HTJS increased the relative abundance of Fusarium, the field disease incidence index did not increase. The soil quality index (SQI), based on the minimum dataset (MDS), showed that HTJS had the highest SQI after the third tillage. Further path model analysis revealed that soil carbon components index and soil physicochemical index were the main controlling factors influencing the SQI. In conclusion, in situ residue return with a compound microbial inoculant (HTJS) is an effective strategy to simultaneously enhance soil fertility and biological activity by regulating the microbial community structure and associated enzyme activities.

To investigate how steam-explosion pretreatment affects humification during sawdust composting, an aerobic composting experiment was conducted using sawdust, chicken manure, and spent mushroom substrate as feedstocks. Two treatments were established—a steam-explosion-pretreated sawdust group (SEW) and an untreated sawdust control (CK)—each with three replicate reactors. Samples were collected dynamically at five key composting stages (initial, heating, thermophilic, cooling, and maturation) for physicochemical, enzymatic, and microbial community analyses. Linear mixed-effects model analysis revealed that enzyme activities were significantly affected by treatment, composting time, and their interaction. SEW significantly enhanced cellulase and polyphenol oxidase activities, and increased laccase and peroxidase activities at specific stages. Compared with CK (humic substances, 75.30 g/kg), SEW promoted higher humic substance accumulation (120.80 g/kg) and altered the dynamics of dissolved organic carbon. Microbial co-occurrence networks in SEW (50 nodes, 602 edges) were more complex than CK (49 nodes, 464 edges), indicating tighter microbial interactions. Path analysis revealed that HS in CK was mainly influenced by DOC and temperature, while HS in SEW was associated with enzyme activities, microbial diversity, and Pseudogracilibacillus. These results suggest that steam-explosion pretreatment enhances substrate transformation and humic substance formation during composting.