Geochemical Characteristics Of Selenium In Soils And Crops In Linshui County,Sichuan Province And Its Implication

Se is an indispensable element of organism.Soil and crops in Linshui County,Sichuan Province exhibit selenium enrichment.So,this area is suitable for developing natural Se-rich agricultural products.In order to study the distribution characteristics of selenium in soil and to plan the producing areas of Se-rich crops in the western part of Linshui County,we systematically collected and analyzed the surface soil,staple crops and their root soil samples.We summarized the distribution characteristics and control factors of Se content in soil and staple crops,established prediction models of Se content in crop grains,and planned the producing areas of Se-rich crops in the study area.The Se content in surface soil varies widely.Its average value（0.21mg/kg）is slightly lower than the average value（0.26mg/kg）of Se in national surface soil and the average value（0.25mg/kg）of Se in surface soil in Sichuan province.However,the areas with high or moderate Se content account for a relatively high proportion.The selenium-rich rate of crops is high and the heavy metal contents of crops do not exceed the national standard.So,the study area is suitable for developing natural se-rich agricultural products.The content of Se in surface soil is mainly controlled by soil-forming parent material.The average content of Se in soil is higher when the soil-forming parent materials are carbonaceous shale,gray-black basalt or iron-bearing basalt and deep-gray limestone.The average content of Se in soil is lower when the soil-forming parent material is Jurassic mudstone and sandstone or Triassic mudstone and limestone.In addition,Se content in soil is mainly related to organic content and sulfur content in soil.The main influencing factors of Se content in crop grains are Se content,S content and organic content in root soil.Soil Se is the main source of Se in crop grains.The absorption of Se by plants is transported by sulfate.Soil S is in the form of SO₄^2-which enters plants together with Se O₄^2-.They show synergistic effect and Soil S promotes the absorption of Se by plants.Humic acid and fine particle colloid produced by soil organic matter putrefaction fix most of selenite in surface soil.At the same time,soil organic matter can adsorb Se or coordinate with Se to form chelate.So,soil organic matter can adsorb and（or）fix Se,thus inhibiting the absorption of Se by crops.Using the Se content prediction models of rice and corn grains and the contents of corresponding elements or indicators of surface soil samples in the study area,the planting area of Se-rich rice farmland is predicted to be 727 hectares;The planting area of Se-rich corn farmland is 16,385 hectares.It provides a scientific basis for the planning of selenium-enriched agricultural products in the study area,and is of great significance for improving the economic value of agricultural products.