Effects Of Different Long Term Management Regimes And Phosphorus On Adsorption And Desorption Of Selenium In Soil

Selenium(Se)is a trace element necessary for human beings,the main route of human intake of selenium is through plant uptake from the soil,the amount of selenium in plants will directly affect the quailty which human intake.Long term different fertilization management measures will affect the properties such as soil organic matter.Organic matter can immobilize and release the selenium,but the effect of organic matter on the adsorption and desorption of selenium and the effect of other competing ions on the adsorption of selenium is not clear.In this study,the effects of two different land use patterns and 5 kinds of long-term different fertilization management measures on selenium adsorption and desorption in soil were discussed.And the effect of phosphate on selenium adsorption and desorption was discussed.Aiming at to provide theoretical basis for the evaluation after exogenous selenium applied into the soil.The main results are as follow:1.The different management measures of soils had a significant effect on the adsorption of selenium.As time increases,the adsorption of selenium on 7 soils was a initially fast followed by slow process,where adsorption equilibrium was all achieved after 8 h.The adsorption capacity of selenium in treatments without crops were significantly higher than the others(Setaside > Fallow);the adsorption capacity of selenite in each soil was NPK > CK > SNPK > M2 NPK > M1 NPK,and the adsorption capacity of selenate in each soil was SNPK > NPK > M2 NPK > M1 NPK > CK.The adsorption capacity of M2 NPK is higher than that of M1 NPK,which had the different soil organic matter contents expect for the other phsical and chemistry properties.The adsorption amount of selenite on the same soil is about 2.83 times of the selenate.Second-order kinetic model(Se(IV)R2 > 0.982;Se(VI)R2 > 0.981).The Langmiur model had better fitting to isotherm(R2 > 0.991).All the Kd values were decreased with the initial concentration of selenium elevate,and it higher in the crop planting soil.The desorption rate increases with the initial concentration of selenium,the desorption rate of soil with high organic matter content is relatively low,showing an immobilization on selenium.2.Phosphate has the different effects on the adsorption of selenium in the soil.With the addition of phosphate and the different concentrations of it,selenite and selenate had different sorption on the soils.The presence of phosphate ions significantly reduced the adsorption of selenite and selenate in soil due to the competitive effect of phosphate and selenium.The binding energy of phosphate is stronger than selenite,the phosphate occupied the specific adsorption sites on soil surface,resulting in the reduction of the adsorption amount of selenite in the soil and resulting in a slight increase on selenate.The adsorption amount of M2 NPK is higher than M1 NPK all the time.When the concentration of selenite was constant,the Kd value decreases with the phosphate ions increase,and when the concentration of selenate was constant,the Kd value increases with the phosphate ions increase.The result of desorption rate is opposite,with the increase of phosphate,the desorption rate of selenite increase,and decrease on selenate.Generally speaking,long-term different fertilization management measures had a significant effect on the adsorption and desorption on selenium,the higher content of organic matter can immobilize selenium.The adsorption of selenium by phosphate ion on soil is related to the valence of selenium in soil,it should be comprehensively considered on the biochemical strengthening of selenium.