BACKGROUND Selenium is one of the essential trace elements for animals and humans, and its abundance is closely related to the health of humans, animals and plants. Selenium deficiency is common in Chinese soil, especially in Tibet. Research results in recent years have shown that the selenium-deficient soils in Tibet are mainly distributed in the north of the Yarlung Zangbo River (referred to as "Yajiang"), while there are areas with high total selenium content and a large area in the south of the Yajiang River. Naidong district is located in the Yajiang River valley in the central and southern parts of the Tibet Plateau. It is one of the important agricultural areas in Tibet and one of the granaries of Tibet.

OBJECTIVES To investigate the distribution characteristics and influencing factors of soil selenium in different areas and different land utilization types on both sides of the Yajiang River in Naidong District, Shannan City, Tibet.

METHODS The contents of selenium and other elements in 1022 topsoil, 30 groups of highland barley seed samples and root soil samples in the Naidong District were determined by atomic fluorescence spectrometry (AFS). Correlation analysis was used to study the influencing factors of soil selenium.

RESULTS The data showed that the arithmetic mean of selenium content in the soil on the north side of the Yajiang River was 0.14mg/kg, which was close to the mean value of selenium in the soil of Tibet (0.15mg/kg). The arithmetic mean of selenium content in the soil on the southern side of the Yajiang River was 0.30mg/kg, which was twice the mean value of soil selenium content in Tibet, and slightly higher than the mean soil selenium content in China (0.29mg/kg). The average selenium content in different land utilization types in the Naidong survey area was cultivated land (0.24mg/kg)>pasture land (0.22mg/kg)>forest land (0.19mg/kg). The research results showed that the soil selenium content on both sides of the Yajiang River in the Naidong survey area was quite different, and there was selenium-rich soil on the south side of the Yajiang River. The factors controlling soil selenium content were not only affected by geological background, but also related to soil pH, organic matter and other factors. Soil Se content increased significantly with the increase of soil organic matter content, but decreased with the increase of soil pH.

CONCLUSIONS It is suggested to make full use of the selenium-enriched soil in Naidong District, and study the absorption of selenium by different crops to improve the availability of selenium in the soil through farmland nutrient management, and promote the development of the local selenium-enriched industry.