Leguminous green manure enhances soil quality and plant productivity in coal mine reclaimed lands: a decade-long field study.

Green manure planting is a commonly used environmentally friendly and sustainable field management practice in resource-constrained agricultural ecosystems. However, the effects of green manure on soil quality and plant production in coal mine reclamation agroecosystems remain unclear. In this study, a decade-long legume cultivation experiment was conducted to evaluate the effects on soil aggregate structure, nutrients, microbial diversity, and plant productivity. The experiment was established at the Gujiao long-term monitoring site of Shanxi Agricultural University and included three treatments: natural restoration, alfalfa planting and villose vetch planting. Compared with the control, legume planting-particularly alfalfa-significantly increased plant biomass and the accumulation of soil organic carbon (SOC) and total phosphorus. Specifically, in the 0-20 cm soil layer under the RAF treatment, SOC and TP contents increased by 23.84% and 47.17%, respectively. Moreover, alfalfa planting enhanced the proportion of aggregates larger than 0.25 mm by 36.56% in wet sieving. Interestingly, continuous legume forage cultivation significantly improved soil aggregate stability. Moreover, alfalfa planting increased bacterial diversity, stimulated the accumulation of lignin-derived compounds, and resulted in the highest acid-formaldehyde ratio, indicating that alfalfa planting increased lignin degradation capacity and provided beneficial nutrients for reclaimed soil. Variance partitioning analysis indicated that both soil physicochemical properties and the microbial community structure co-driven plant biomass variations. These findings clarify the mechanisms by which legume cultivation improves soil quality, enhances microbial diversity, and increases biomass production. In conclusion, this study supports the application of leguminous green manure as a natural solution for coal mine land reclamation, contributing to soil quality improvement and fostering sustainable development in postmining ecosystems.