Concentration And Profile Distribution Characteristics Of Selenium In Hunan Province

Selenium is a beneficial element.The source of selenium in the human body is mainly food and water.Long-term selenium intake will cause endemic diseases such as Keshan disease and Kashin-Beck disease.Excessive intake may lead to selenium poisoning.The soils developed in the lime stones of the central and southern Hunan and the river and lake sediments of the northern area have higher selenium content.By the end of 2017,Hunan province had developed more than one million mu of selenium-enriched cultivated land.Studies have shown that selenium content and migration in soil are closely related to parent material,p H,organic matter and land use patterns.Therefore,in order to more comprehensively clarify the selenium content and distribution characteristics of soil in Hunan Province,this study used the soil samples collected from 133 typical dry land profiles and 60 typical paddy soil profiles derived from 7 parent materials in Hunan(shale,quaternary red earth,sand shale,granite,purple sandstone,limestone,lake and river sediments),and the contents of soil selenium and available selenium and soil physical and chemical properties were analyzed.The effects of soil parent material,soil type and land use on soil selenium and available selenium content and their profile distribution were studied to provide a scientific basis for the establishment of the soil selenium database in Hunan Province and the rational development of selenium-enriched products.The conclusions are as follows:(1)There were significant differences in total selenium and available selenium content in the tested soils under different planting patterns,dry land soil was generally larger than that in paddy soil,and the average selenium content in topsoil(0-20 cm)and weighted A layer soil was 0.678 mg/kg and 0.655mg/kg for dry land soil,and was 0.426mg/kg and 0.401mg/kg for paddy soil,respectively;The average available selenium content in the topsoil(0.014mg/kg)was 1.6 times that of paddy soil(0.009mg/kg).Compared with other parent materials,the content of selenium and available selenium in dry land soil and paddy soil derived from shale and sand shale was higher.According to the Selenium-rich soils grading scales(normal selenium: 0.200~0.400mg/kg,selenium enrichment: 0.400~3mg/kg),Most of the soil in Hunan has normal selenium content or selenium-rich,63.9% of dry lands soils and 38.33% of paddy soils A layer is rich in selenium.Selenium content in topsoil of soil profile which derived from limestone of Dawei mountain is: red soil(0.94mg/kg)<yellow soil(1.37mg/kg)<mountain meadow soil(1.42mg/kg)<yellow brown soil(1.44mg/kg).(2)The study on the profile distribution of selenium in the tested soil showed that the profile distribution type of selenium in dry land soil and paddy soils were similar,with the topsoil aggregation type being the main ones,followed by mid-soil aggregation type,the subsoil aggregation type,top-subsoil aggregation type and homogeneous type.There are some differences in the profile distribution of selenium in the mountain soils derived from limestone.Among them,only the mountain shrub meadow soils have obvious topsoil aggregation characteristics,and the distribution characteristics of selenium in other mountain soil profiles are not the same.(3)Correlation analysis results show that the total selenium content in the surface layer of dry land soil shows an inheritance od matrix,and the total selenium content in layer A was significantly positively correlated with the total selenium content in layer C(r=0.264*,n=57).Soil total selenium was significantly positively correlated with soil organic matter(r=0.400**,n=864);soil total selenium was significantly positively correlated with total iron and total aluminum content(r=0.077**,n=865;r =0.184**,n=865),p H was significantly negatively correlated with soil selenium(r=-0.316**,n=865).Bioaccumulation enriches selenium in the soil surface.p H and clay minerals(iron-aluminum oxide,etc.)affect the selenium content and distribution in the soil by controlling the sequestration and migration of selenium in the soil.(4)Statistical analysis of the topsoils silicon-aluminum-iron ratio(saf)of the tested soil showed that the saf value of the same type of soil is: subsoil aggregation type < top-subsoil aggregation type < homogeneous type,mid-soil aggregation type < topsoil aggregation type.For specific profile distribution type of selenium,the saf value of topsoil in dry land is smaller than that of paddy fields.C limate can affect the content and profile of selenium in soil by affecting bioaccumulation and leaching,as well as the process of volatilization and sedimentation of selenium.