Ameliorative effects of synergistic straw returning and lime application on acidic paddy soils in South China

Soil acidification constrains the rice production potential in South China. This study mainly explored the effects of combining straw return with lime application for ameliorating acidic soils, aiming to provide a practical basis for improving di-silicated and aluminum-rich acidic soils in the South China region. A double-rice (early and late season) field experiment was conducted with four treatments: conventional fertilization (CF), conventional fertilization + quicklime (CFL), conventional fertilization + straw return (CFS), and conventional fertilization + straw return + quicklime (CFSL). Rice yield, soil physicochemical properties, organic carbon fractions, enzyme activities, and microbial community structure were systematically measured. The results showed that, compared with the CF treatment, the CFSL treatment increased rice yield by 2.22%−29.57%. For soil acidification indicators, both the CFL and CFSL treatments significantly reduced exchangeable acidity and exchangeable aluminum contents, while soil pH increased significantly by 0.60 and 0.36 units, respectively. Treatments CFS and CFSL also significantly increased soil cation exchange capacity (CEC) by 17.72% and 20.58%, respectively. In terms of soil organic carbon, compared with CF, the CFSL treatment increased microbial biomass carbon and dissolved organic carbon contents by 26.53% and 34.20%, respectively; concurrently, the activities of soil urease, β-glucosidase, and invertase were enhanced by 33.60%, 19.49%, and 13.89%, respectively. Microbial community structure analysis further revealed that the CFSL treatment not only increased the relative abundance of the bacterial phylum Proteobacteria, but also significantly enhanced fungal community alpha diversity, and drove a pronounced “trade-off” in abundance between Ascomycota and Basidiomycota, thereby reshaping the composition and functional profile of the microbial community. In conclusion, the integrated technology of straw return combined with lime amendment optimized the chemical properties and microbial community structure of acidic soils, effectively alleviated soil acidification, promoted stable and increased rice yields, and provided an efficient and feasible technical approach for ameliorating acidic soils in South China.