Geochemical characteristics and geological genesis of soil selenium anomaly zone in the Hetao Plain, Inner Mongolia, and crop biological effects-based assessment of selenium-rich cultivated land development potential

Abstract

Exploring the geological genesis of selenium (Se) in Se-rich soil of the Hetao Plain, a major grain production base of corn, wheat, potato, sunflower and zucchini in northern China, is vital for the rational development of Se-rich land resources and the environmental geochemical assessment. In this study, element geochemical characterization, geospatial analysis and mathematical statistics were employed to investigate the factors influencing the spatial distribution of soil Se in the Hetao Plain, focusing on the differences in soil chemical weathering intensity, rare earth elements distribution pattern and soil sedimentary sequence characteristics between the study area and typical surrounding parent materials. The results indicated that the soil Se content in the study area ranged from 0.07 mg/kg to 0.72 mg/kg, with an average value of 0.24 mg/kg, which was higher than the regional background values. Moreover, this suggested that local Se enrichment occurred in the soil of study area, and that the Se distribution was restricted by factors including soil clay minerals, constant elements and soil organic matter (SOM) contents. The characteristics of soil parent material in the study area differed significantly from those of the piedmont diluvial parent material, whereas were similar to those of the Yellow River floodplain and lacustrine parent materials, revealing that the soil parent material in the study area mainly came from the water system transportation. Through combining the characteristics of soil sedimentary sequences in the study area with the location of the Yellow River ancient channel, it is suggested that the origin of high Se soil in the central and northern belt zone of the study area is associated with the Yellow River ancient channel, where the enrichment pattern is “channel sedimentary type”. In addition, the development and utilization potential of Se-rich cultivated land was explored based on the biological effects of Se. It was concluded that the Se content of crops (corn, sunflower and zucchini) in the study area was higher than that of similar crops in China, that crop species and soil Se content were the dominant influencing factors of crop Se content in the study area, and that the crops growing in Se-rich areas had higher Se enrichment rate than those growing in non-Se-rich areas. This exhibited a high development and utilization potential of the investigated cultivated land for Se-rich crop production.