Objective The soil in Xiayi County, Henan Province, is rich in selenium (Se), an essential element for human health. However, systematic research on the geochemical characteristics and genesis of selenium in this selenium-enriched soil has not yet been conducted. Based on field measurement data, this study thoroughly investigates the geochemical distribution patterns and controlling factors of selenium, aiming to provide scientific support for regional land planning.

Methods Based on 980 surface and 85 deep soil samples from selenium-rich soils in Xiayi County, Henan Province, this study employs mathematical statistics, correlation analysis, single-index evaluation, and comprehensive assessment methods to analyze the geochemical characteristics of selenium-enriched soils. It investigates the influences of parent material, organic carbon, soil elements, pH, and soil depth on selenium content, and conducts environmental quality assessment as well as analysis of development potential.

Results The results indicate that: the average selenium content in surface soil is 0.20 μg/g, which is consistent with the background value of the Henan region. The coefficient of variation is 31.4%, indicating moderate variability and an uneven distribution, with local enrichment observed; the selenium content in deep soil layers is consistently less than 0.2 μg/g, showing a negative correlation with soil depth and presenting a typical surface enrichment pattern. An area of 32.24 km² was dlineated as selenium−rich soil, primarily located in the northern and eastern parts of Xiayi County. Soil parent material is one of the factors influencing selenium content; coal−bearing strata and black shale are significant sources of selenium. There exists a positive correlation between organic carbon and selenium levels, with organic carbon being notably enriched; fertilization or application of organic manure promotes an increase in soil selenium content. Additionally, elements such as nitrogen (N), phosphorus (P), manganese (Mn), molybdenum (Mo), iodine (I), strontium (Sr), fluorine (F), lead (Pb), zinc (Zn), nickel (Ni), mercury (Hg), chromium (Cr), arsenic (As), and cadmium (Cd) show positive correlations with selenium, while only calcium oxide (CaO) exhibits a negative correlation with it. Furthermore, organic carbon, Hg, Cd, N, Se, and I are significantly enriched in surface soils and contribute to a synergistic effect on selenium enrichment; soil alkalinity does not affect the selenium content in soils. Overall, the quality of soils within the study area is good; clean land covers an area of 1087.00 km², accounting for 99.91% of total land area; the areas classified as moderately selenium−rich and selenium−rich grades have been delineated, with a total area of 267.29 square kilometers, accounting for 24.57%.

Conclusions The selenium content in the surface soil is consistent with the background values of the Henan region, indicating a localized enrichment characteristic. The selenium levels in the soil are closely related to factors such as soil parent material, organic carbon, and various physicochemical indicators. There exists a synergistic mechanism among organic carbon, mercury (Hg), cadmium (Cd), nitrogen (N), and iodine (I) concerning soil selenium enrichment. The regional soil quality is generally favorable, and selenium−rich soil is mainly distributed in the east and north of Xiayi County.