Spatial Distribution of Soil Nutrients in the Red Beds of Southern China and Their Responses to Different Land Use Types

This study aims to understand the spatial variability of soil nutrients in red-bed regions and identify the environmental factors driving their distribution. We analyzed the spatial distribution and key drivers of pH, soil organic matter, nitrogen, phosphorus, potassium, and their available forms across forestland, cropland, grassland, and bare land in Nanxiong Basin, South China, using principal component analysis, semivariogram analysis, and ordinary Kriging interpolation. Soil organic matter and total nitrogen exhibited moderate variability (CV = 28.64% and 29.81%) driven by topography and vegetation. Available nitrogen showed low variability (CV = 17.91%), reflecting regulation by large-scale ecological processes. In contrast, available phosphorus demonstrated the highest variability (CV = 37.14%), shaped by localized fertilization and erosion. Unique interactions between topography and hydrology were governed by nutrient patterns in grasslands, while anthropogenic homogenization dominated croplands. Semivariogram analysis revealed strong spatial dependency for phosphorus, reflecting natural regulation, while weak dependency for potassium highlighted human-induced randomness. This study also identified capillary water capacity as a key driver in grassland nutrient cycling, adding to our knowledge of soil–water–plant interactions. Together, these findings provide a scientific basis for integrating precision agriculture and ecosystem-based strategies to enhance soil fertility and resilience in red-bed regions under diverse land use conditions.