Abstract: The organic sorghum base in Maoba Town of Renhuai City was taken as the research object to study the geochemical distribution and occurrence form characteristics of soil selenium. The results showed that soil selenium content in sorghum base ranged from 0.24 to 1.35 mg/kg, with an average of 0.50 mg/kg, which was 1.72 times of the national soil background value. Se-enriched soil was widely distributed in the study area, accounting for 50% of the total area. The main chemical forms of soil selenium were organic-sulfide bound and elemental selenium, accounting for 57.14%. The contents of Fe-Mn oxide bound selenium, exchangeable-carbonate bound selenium and residue selenium were not much different, accounting for 14.21%, 14.19% and 12.70%, respectively. The water-soluble selenium was the lowest （1.76%）. The sum of water-soluble selenium and exchangeable-carbonate bound selenium was relatively high （15.95%）, which indicated that the bioavailability of soil selenium was strong, and it was easy to be absorbed and utilized by plants, and was beneficial to the cultivation and production of Se-enriched crops. The content of total selenium and various forms of selenium in soil was positively correlated with organic matter, indicating that the increase of organic matter was beneficial to the accumulation of selenium in soil. Soil pH was significantly positively correlated with water-soluble selenium content, but weakly negatively correlated with total selenium and other forms of selenium content. It was confirmed that selenium mainly existed in the form of selenate under alkaline conditions, which improved the bioavailability of selenium. Therefore, the sorghum base in the study area had a high level of selenium enrichment, a large distribution area, and a strong bioavailability of selenium, which provided a good land resource condition for improving the quality of sorghum Hongyingzi,and developing local Se-enriched characteristic agricultural products.

Key words: sorghum base soil, selenium, geochemical distribution, occurrence forms, Se-enriched soil evaluation, Maoba Town, Renhuai City