Delimitation of natural Se-rich land in Sanhe Town, Haidong City, Qinghai Province, China

Based on the 1∶50 000~1∶2 000 land quality geochemical survey data and the requirements of the Delimitation and the Logo for Natural Selenium-enriched Land (DZ/T 0380—2021), this study evaluated the selenium (Se) content, environmental quality, fertility quality, and irrigation water quality of soil in Sanhe Town, Ping'an District, Haidong City, Qinghai Province. The evaluation results show that: (1) The soil in Sanhe Town was alkaline; (2) The soil Se content ranged from 0.093×10^-6 to 1.938×10^-6, averaging 0.425×10^-6; (3) The Cd, Hg, Pb, and Cr contents in the soil were all below the risk screening values of soil for agricultural land, while the As content in the soil in the southern portion of the study area was higher than its risk screening value; (4) The quality of irrigation water met the standard specified in the Green Food-Environmental Quality for Production Area (NY/T 391—2013), and the soil fertility was characterized by rich available phosphorus and potassium, and moderate nitrogen and organic matter. Based on the above evaluation results, this study delimited contiguous natural green Se-rich land of 40.46 km², including 12% directly usable arable land (4.76 km²), and 88% potentially usable grassland (7.84 km²) and forest land (27.86 km²). They are distributed primarily in six villages, including Zhangqizhai, Luotuobao, Xicun, Dongcun, Qixinzhuang, and Sanhe villages. Considering the Se-rich industry planning and local conditions, this study proposed developing Se-rich planting in arable land and Se-rich animal husbandry by utilizing natural Se-rich forage in forest land and grassland.