Origin, distribution and enrichment of selenium in oasis farmland of Aksu, Xinjiang, China

This study aims to investigate the selenium (Se) distribution in the soils of the vast cultivated areas of Aksu Prefecture in mid-Western Xinjiang of Northwest China. The study of the origin and enrichment mechanism of Se in the soils of alluvial fans of these areas (also known as oasis areas) are of great importance for the conservation and development of Se-rich resources. Geological genetic analyses and elemental abundance comparisons confirmed that the Se-rich basement rocks (i.e., the Xiyu Group) are the primary source material of Se in the oasis farmlands. The study, carried out on samples taken along two transects that cross each other, showed that, from the peripheral to the core farmland of the investigated area, the Se concentration increases significantly, accompanied by a decrease in pH and increases in organic matter and clay particles. The peripheral farming land in Aksu showed low median Se concentration of 0.19 mg/kg that represent the regional soil background, high alkalinity (pH = 8.1-9.4), high silica content (SiO2 = 47.8-72.0 wt%) and low organic matter content (OrgC = 0.17-0.76 wt%). The core farming land, representing the intensely cultivated farmland, showed a median Se content of 0.56 mg/kg, and is characterized by low alkalinity (pH = 7.3-8.5) and silica content (SiO2 = 33.5-52.5 wt%), and is rich in organic matter (OrgC = 0.87-9.8 wt%). Based on the vertical soil section investigation, we found that the soil mineralogical and geochemical variations from the deep to the shallow soil layers is similar to that from the peripheral to the core farming land. Thanks to soil acidification and accumulation of organic matters and clay particles, the oasis-type farming activities transfer Se from the Se-enriched parts of the peripheral farming land and the deep soil layers to the upper soil layers of the core farming land. This Se-enrichment mechanism made the core farming land and its topsoil the most Se-rich part of the investigated area.

Automated summary

The study aims to investigate the distribution of selenium in the soils of cultivated areas in Aksu Prefecture in Northwest China. Results revealed that selenium in oasis farmlands primarily comes from selenium-rich basement rocks, with significant variations in selenium concentration and soil properties between peripheral and core farming lands.