Synergistic Amelioration of Acidic Purple Soil through Combined Application of Calcareous Purple Parent Rock and High-Rate Organic Fertilizer

Objective This study aimed to develop feasible integrated strategies for ameliorating soil acidity and enhancing biological fertility in purple soils, thereby providing a scientific basis for sustainable remediation of acidic purple soil.

Method A 120-day laboratory incubation experiment was conducted using acidic purple soil derived from Jurassic Shaximiao Formation (J₂s) mudstone as the substrate. The ameliorative effects of applying 0.1%, 0.3%, and 0.5% calcareous purple mudstone from the Jurassic Suining Formation (J₃sn), alone or in combination with 5% or 10% composted sheep manure, were systematically evaluated.

Result Both individual and combined applications of calcareous purple parent rock and organic fertilizer had an ameliorative effects on the acidity of purple soil. Addition of the calcareous purple parent rock reduced soil acidity and increased exchangeable base cations and base saturation. Compared to calcareous parent rock amendments, the combined application with high-dose organic fertilizer exhibited more pronounced improvements. In the work, the treatment of 0.5% calcareous purple parent rock + 10% organic fertilizer shown optimal performance—increasing soil pH by 1.99 units and reducing exchangeable acidity by 92.1%. Beyond acidification mitigation, this combined treatment significantly enhanced soil organic matter content and promoted microbial community richness and diversity. It increased the relative abundances of bacterial phyla including Myxococcota, Firmicutes, Proteobacteria, Actinobacteriota, Gemmatimonadota, and Bacteroidota, while decreasing those of Cyanobacteria, Acidobacteriota, Patescibacteria, Chloroflexota, and Planctomycetota. The relative abundance of fungal Ascomycota was also elevated.

Conclusion Considering both effectiveness and cost-efficiency, a “dual 1%” strategy—co-applying 1% calcareous purple parent rock and 1% organic fertilizer—is recommended for practical application. This approach enables the resourceful utilization of local calcareous parent material and agricultural organic waste, achieving dual benefits of soil acidification remediation and biological fertility enhancement in purple soil regions.