Spatiotemporal Evolution of Soil Nutrients in Land Consolidation Areas: A Random Forest Model-Based Perspective from Anyi County, Jiangxi Province

Understanding the long-term spatiotemporal dynamics of soil nutrients in land consolidation areas is essential for sustainable land management. In this study, the changes in soil organic matter (SOM), available nitrogen (AN), available phosphorus (AP), available potassium (AK), and soil pH from 1980 to 2023 in the land consolidation area of Anyi County, China, were investigated. A random forest (RF) model was developed using multisource environmental variables, including climate, topography, remote sensing, vegetation, parent material, distance to rivers, and land use. The results revealed three key findings. First, while land consolidation significantly increased overall soil nutrient levels, trends for individual nutrients were highly variable: AP and AK continuously increased over the 40-year period. SOM and AN increased after consolidation but decreased in later years. This process was accompanied by systematic soil acidification. Second, land consolidation substantially restructured the spatial patterns of soil nutrients. SOM and AN became more homogeneously distributed, whereas AP and AK showed increased variability. High-value nutrient areas shifted from contiguous expansion in the early stages to local aggregation and patchy fragmentation over the long term. Third, the RF model demonstrated high predictive accuracy (R2 = 0.70 for pH, 0.68 for SOM, 0.63 for AP, and 0.54 for AK), with variable importance analysis identifying distinct environmental drivers for each nutrient. These findings provide a scientific basis for precision fertilization and evidence-based land consolidation planning.