Influence factors of soil selenium in cultivated area of Nangqian County, Qinghai Province

The results of geochemical evaluation of soil quality show that there is large area of selenium-rich (Se>0.30 mg/kg)sufficient (0.15 < Se≤0.30 mg/kg) land (65.25 km²) in cultivated area around Nangqian County.Selenium-rich/sufficient soil shows a good inheritance of parent material.Meanwhile, soil selenium content is affected by natural factors including geochemistry, environment for soil formation, soil type/texture and soil properties.Meadow soil (soil Se content ranging between 0.08 mg/kg and 0.69 mg/kg with an average of 0.26 mg/kg) and chestnut soil (soil Se content ranging between 0.20 mg/kg and 0.42 mg/kg with an average of 0.32 mg/kg) are the main selenium-rich soil types.Soil Se content generally shows an opposite trend of pH.Selenium is more liable to be enriched in red clay and black clay with higher loamification level and finer particles.Higher organic matter (ranging between 12.1 g/kg and 98.6 g/kg with an average of 30.8 g/kg) and iron-aluminum oxides content (from 2.86% to 6.34% with an average of 4.34% and from 10.07% to 17.87% with an average of 13.59%, respectively) are advantageous to soil selenium enrichment as well.