Comparative Assessment of Diverse Green Manure Species for Enhancing Soil Quality, Microbial Communities, and Earthworm Growth in Fallow Paddy Fields

The excessive use of chemical fertilizers is a primary driver of soil degradation in agricultural systems. Planting green manure during fallow periods offers a sustainable alternative for soil conservation. The present study investigated the effects of different green manure cropping systems (Ryegrass (TR), Chinese milk vetch (TM), and Spinach (TS)) on soil physicochemical properties, biological activity, and microbial communities, compared to a control (CT). Results demonstrated that green manure treatments significantly enhanced soil fertility by increasing the content of soil organic matter (SOM), available nitrogen (AN), available phosphorus (AP), and available potassium (AK). Notably, the TR treatment increased SOM, AN, and AP by 23.0%, 60.0%, and 44.6% (p < 0.05), respectively. Concurrently, key soil enzyme activities (urease, dehydrogenase, catalase) were significantly boosted (p < 0.05), with TR showing the most pronounced effect. Earthworm indicators (such as earthworm biomass and abundance) were significantly higher in the Ryegrass plots (p < 0.05). Microbial analysis revealed that TM enhanced bacterial diversity, whereas TR increased fungal richness (p < 0.05). Beneficial bacterial phyla, particularly Proteobacteria, exhibited a marked increase under the TM and TR treatments, while the fungal community underwent a favorable shift. Consequently, a significant elevation was observed in the overall Soil Quality Index (SQI) across all green manure treatments. Notably, the TR treatment resulted in a substantial 150% increase. In summary, ryegrass emerged as the most effective treatment in enhancing soil fertility, biological activity, and microbial diversity, underscoring its considerable potential as a green manure for sustainable soil management during fallow periods in paddy fields.