This paper is the result of environmental geological survey engineering.

Objective Both Se-rich farmland soils and low−Se farmland soils in Keshan disease and Kashin−Beck disease areas are distributed in Luoyang City. Analyzing the spatio-temporal variation characteristics and influencing factors of Se content in farmland soils of Luoyang City is of great ecological significance for the development of Se-rich land resources and the prevention and control of Keshan disease and Kashin−Beck disease.

Methods Based on the multi-target regional geochemical survey data in Luoyang City, 181 representative sampling sites were selected for re-sampling. Indicators including total soil carbon (TC), organic carbon (OC), and pH value were analyzed. Methods such as growth rate calculation, spatial interpolation of content, and Pearson correlation analysis were employed to investigate the spatio−temporal variation rules and controlling factors of Se. Furthermore, the ecological effects of Se spatio−temporal variation on the development of Se-rich characteristic agricultural industry and human health (including Keshan disease and Kashin-Beck disease) were evaluated.

Results The high Se background areas of farmland soils in the study area are mainly distributed in carbonate development regions, basin areas, and the peripheries of urban zones, where the Se content in surface soils shows an increasing trend. In contrast, the areas affected by Keshan disease and Kashin-Beck disease are low Se background zones, characterized by a decreasing trend of Se content. Among all soil types, Shajiang black soil exhibits the highest Se concentration. Se is significantly enriched in the surface soils. Se shows significant positive correlations with OC, TC, Nitrogen (N), and Cadmium (Cd) in spatio-temporal terms, a weak negative correlation with pH. The correlations between Se and other elements and oxides vary spatially and temporally.

Conclusions The high Se background areas in the study area possess a stable ecological environment suitable for the sustainable development of Se-rich crops. The depletion of Se and Molybdenum (Mo) in the soils of Keshan and Kashin-Beck disease areas poses potential health risks to residents. Se distribution in farmland soils is mainly significantly controlled by terrain, parent material, OC, TC, N, Cd, and anthropogenic activities, while pH exerts a relatively weak impact.