Selenite adsorption and desorption in main Chinese soils with their characteristics and physicochemical properties

Abstract

Selenium (Se) adsorption influences its mobility, transformation, and bioavailability in soil. Se interactions with soils and soil constituents have focused primarily on selenite retention. The dominant factors of selenite adsorption behavior and the impacts of exogenous Se concentration were investigated for the prediction of the rate of retention and release of selenium species in soils and the guidance of Se supplementation implementation. Eighteen typical agricultural soils with varying physicochemical characteristics and mineralogical composition were collected throughout China for the study of their adsorption and desorption behavior toward selenite and the effect of their physicochemical properties. Results showed that Se adsorbances among 18 soils varied considerably. Among numerous soil properties and components, soil pH exerted a significant negative effect on selenite adsorption in soil, whereas amorphous iron and amorphous aluminum had positive effect (P < 0.05). Organic matter (OM) showed an indirect effect when high concentrations of selenite were present in soil. Moreover, soil carbonate content imposed an indirect effect on selenite adsorption in soil. Selenite desorption showed a reverse trend compared with adsorption: the correlations of desorption rate with soil pH and amorphous iron were positive and negative, respectively (P < 0.05). The soil/solution distribution coefficient (K d) had no significant correlation with soil properties, other than with pH (P < 0.05), but the K d values of different soils were highly variable. The observed adsorption behavior of selenite in soil is complicated: small amounts of exogenous Se were mainly adsorbed by a monolayer physical process, but multilayer adsorption occurred when the concentration increased. The soils that strongly adsorb selenite often showed low desorption rates, as well, which largely limited the migration, transformation, and bioavailability of selenite in soils. Therefore, residue problem must be considered when Se fertilizers are applied to these soils.