Role of sulphate in affecting soil availability of exogenous selenate (SeO42-) under different statuses of soil microbial activity

Abstract

We investigated sulphate application, different statuses of soil microbial activity and their joint effects as variables associated with changes in potentially plant-available selenium (Se_ppa) and soil Se fractionation during the course of an incubation study. The time-resolved behaviour of added selenate (400 µg Se/kg as Na₂SeO₄) in two agricultural soils was elucidated by means of single extraction (50 mmol/L NH₄H₂PO₄), sequential extraction procedure (SEP) and chemical speciation analysis in phosphate extracts. The decrease in phosphate-extractable Se, a consequence of soil aging, was inhibited by sulphate (by 34% and 29% in Chernozem and Cambisol, respectively) and by gamma-irradiation (by 46% and 20% in Chernozem and Cambisol, respectively) after 72 days of incubation as compared to the control treatments. Glucose amendment dramatically decreased Se_ppa only in the Chernozem. After 1 year, the initial soil treatment with respect to inhibited or stimulated microbially-mediated processes substantially controlled the distribution pattern of exogenous Se as observed using the SEP. Application of sulphur fertilisers and sources of labile organic matter is thus an essential agronomic practice to correct unfavourable amounts of Se_ppa.