Multi-Scale Driving Mechanisms of the Spatiotemporal Distribution of Soil pH in High-Standard Farmland Within the Hilly Regions of Southern China

Elucidating the multi-scale driving mechanisms of the spatiotemporal distribution of soil pH is critical for regional soil ecological regulation and the preservation of cultivated land fertility. However, systematic elucidation of the multi-scale driving mechanisms of the spatiotemporal distribution of soil pH remains limited. Here, we integrated random forest, XGBoost, and geographically interpretable SHAP (GeoShapley) to systematically investigate the spatiotemporal changes in soil pH and their driving mechanisms across three analytical scales (global, raster, and point-level) before and after high-standard farmland construction, based on 149 paired soil sampling points collected in 2008 and 2023 in Taihe County, Jiangxi Province. The mean soil pH in the study area increased from 5.12 in 2008 to 5.53 in 2023, suggesting mitigation of soil acidification. XGBoost outperformed random forest in both periods, with R2 values of 0.71 and 0.67 for the two periods, respectively, and the spatial predictions indicated that soil pH in the western and southeastern regions increased following high-standard farmland construction. At the global scale, feature importance based on XGBoost indicated that climate contributed most to soil pH variation in both periods, followed by anthropogenic activities. At the raster scale, GeoShapley revealed a shift from a combination of anthropogenic activities and climate in 2008 to an interplay among climate, vegetation, and topography in 2023, suggesting a decreasing influence of anthropogenic disturbance. At the point level, the factors primarily influencing soil pH shifted from topographic and anthropogenic ones in 2008 to topographic and climatic ones in 2023, regardless of whether the sampling points exhibited low or high pH values, further corroborating the diminishing role of anthropogenic influence. Interaction analyses indicated that topography and vegetation consistently modulated the effects of anthropogenic and climatic factors throughout the study period, suggesting that these two factors were consistently associated with soil pH dynamics across the study area. In summary, this study provides a scientific basis for the targeted improvement of cultivated land fertility and the formulation of differentiated soil management strategies for high-standard farmland in the hilly regions of southern China.