Study On Soil Selenium Species And Availability Of Soil Under Different Land Uses In Mingshan River Watershed

Selenium which is important to the human body is one of the essential trace elements for human, so the study of its stocks, bioavailability and influencing factors has great significant. We choose two kinds of land use (arable land and tea garden), two soils (yellow soil and purple soil), two soil depth(0-20cm and 20～40cm) of soil in Mingshan river watershed, using sequential extraction method to abstract species of selenium, using digestion method to abstract total selenium and effective selenium, and then determining the content of selenium by hydride generation-atomic fluorescence spectrometry(HG-AFS).Find the factors which can influence the content of effective selenium, so that provide reference and theoretical basis for the development of the local rich tea industry. The main conclusions are as follows:The content of selenium Mingshan river watershed is 396.82μg·kg-1, above the national average, belong the middle selenium area. In which the content of selenium in arable land is higher than tea garden,0～20cm depth is higher than 20～40cm depth, although the content of selenium has little difference between yellow soil and purple soil, but in the purple soil the content of selenium is higher than the yellow soil which in the cultivated land, and opposite in the tea garden soil. It illustrates that the different modes of farming, human activity factors and the natural environment have a greater impact on the content of selenium.In the absence of exogenous selenium added, the soil total selenium mainly from the soil parent materials. In addition to the parent material, the physical and chemical properties of the soil itself can have a significant impact on the content of total Se and its distribution. Through the study of soils of different land uses, different soil types, different layers of we found that the organic matter, CEC, pH, active iron have a impact on the Se in varying degrees, of which the most important is the organic matter and CEC.There are five kinds of selenium to be extract by Continuous extraction method, the content of various forms of selenium of the soil and its utilization are inversely proportional, expressed as soluble selenium< selenium bound to organic matter< selenium bound to iron and manganese oxides< exchangeable and selenium bound to carbonate< residual selenium. The soluble selenium which most easily absorbed by plants is little, but the residual selenium which can not absorbed by plants is more, it is showed that the extent of the use of soil selenium of Mingshan river watershed is not high, but the reserves are abundant. Under certain conditions, conversions between the various forms of selenium in the soil will happen by hydrolysis and microbial action, soil properties can contribute to the occurrence of these reactions/which include pH, organic matter, CEC, iron, aluminum, these factors are mainly affected by the valence of selenium to influence the distribution of various forms of selenium in the soil.The content of effective selenium in Mingshan river watershed is 73.20μg·kg-1, only 18% of the total selenium, this shows the extent of the use of selenium in the soil is not high. The content of effective selenium of arable land is less than tea garden, yellow soil below the purple soil, the soil of second layer below the topsoil. The most easily absorbed by plants in various forms of selenium is soluble selenium and exchangeable selenium, both with an effective positive correlation between effective selenium. The results show that there is a significant positive correlation between Fe-Mn oxide bound selenium and selenium effectively, this shows that Fe-Mn oxide bound selenium as the potentially be exploited section in soil, with changes in soil environment can become a part of the soil selenium which can be utilized, therefore, it is very important to improve the soil environment for various forms of selenium in order to increase the effectiveness. There are many factors influence the effectiveness of selenium, this paper discusses the effects of soil properties on the effective selenium of its content and distribution.Soil pH of Mingshan river watershed is positively correlated with effective selenium, this shows that the alkaline soil is conducive to plant for the absorbion of selenium,the pH affects its validity through converting valence of selenium; The role of selenium in soil organic matter is release, the higher the OM. is the more the effective selenium has; the more CEC the more effective selenium in soil; since the strong adsorption capacity almandine can reduce the effectiveness of selenium, through the action of pH may enhance complexation, this is an important reason of the selenium for not releasing.