Spatial Variation Patterns and Pedogenic Environment Analysis of Typical Selenium-Rich Farmland Soils

Selenium (Se) is an essential trace element for the human body, and farmland soil is the primary source of Se in the food chain. Ximeng County is a typical Se-rich plateau region in Yunnan, China. The study area was selected from a representative region of Ximeng County. A total of 136 farmland soil samples were collected in the study area to determine and analyze the effects of soil factors (soil pH, organic matter, clay content, sand content, silt content), topographic factors (elevation, slope, aspect), climatic factors (runoff, rainfall, temperature), and natural factors (land use type, soil type) on soil Se concentration. Using Geodetector analysis, the study assessed the extent to which these factors influence soil Se concentration and the impact of interactions among them. The results indicate that the average total Se content in the study area was 0.48 mg·kg−1, exceeding the background values for soil elements in Yunnan Province. In terms of spatial distribution, total Se and available Se were primarily concentrated in the southeastern and western parts of the study area; using the factor explorer in Geodetector, it was found that elevation, rainfall, runoff, temperature, and silt content significantly influenced the concentrations and spatial distribution of total Se and available Se, with elevation having the greatest impact. Interaction analysis revealed that all pairwise interactions among the 13 influencing factors exhibited nonlinear two-factor enhancement. Among these, the interaction between slope and elevation provides the strongest explanation for the spatial variation in total Se and available Se. A combined correlation and Geodetector analysis revealed that the Se enrichment in the study area is primarily influenced by the combined effects of elevation, climatic factors (runoff, rainfall, temperature), and organic matter content. This study is of great significance for land resource management in Se-rich areas, the development of Se-rich agricultural products, and the implementation of targeted policies.