Distribution and influencing factors of selenium content in soil in karst areas in Mashan County, Guangxi, China

This study aims to investigate the distribution characteristics of the total selenium content in soil in karst areas in Mashan County, Guangxi and to explore the effects of different soil parent materials, land uses, and soil types on the selenium content in soil. To this end, 492 samples of surface soil (0~20 cm) were collected from the northern part of Mashan County and the distribution of the total selenium content in the samples were studied by statistical methods. The results are as follows. The total selenium content in the soil varies from 0.20×10^-6 to 3.54×10^-6, with an average value of 0.76×10^-6. Meanwhile, the selenium-rich area accounts for 98.29% and the coefficient of variation is 34.49%. The soil in the Permian Heshan formation bearing black shales and coal-measure strata has the highest selenium content, with an average of 1.17×10^-6, while the Carboniferous Maping formation has the lowest selenium content, with an average of 0.64×10^-6. In terms of different soil types, the lateritic red soil has the highest selenium content, with an average value of 1.04×10^-6, while the fluvo-aquic soilhas the lowest selenium content, with an average value of 0.56×10^-6. In terms of land use types,the forestland and orchard have a high selenium content in soil, while the paddy field, grassland, and arid land have a low selenium content. Therefore, the selenium content in soil in the study area is mainly affected by soil parent materials, with the selenium enrichmentin soil being affected by the organic matter content to a certain extent.