Influence of submergence and subsequent drainage on the partitioning and lability of added selenium fertilizers in a Sri Lankan rice soil

Abstract

The influence of submergence (anaerobic conditions) and subsequent drainage (aerobic conditions) in rice soils on the partitioning and lability of Se fertilizers was studied. We used an isotope dilution method to examine the time-dependent changes in the partitioning and lability of Se in a Sri Lankan rice soil following fertilization with selenite (Se(IV)) and selenate (Se(VI)) (1 mg kgˉ¹) and incubation under anaerobic (30 d) and subsequent aerobic conditions (7 d) mimicking rice paddy water management practices. The Kd values for Se(IV) were significantly (P ≤ 0.001) higher than those for Se(VI) in all treatments and sampling times. The K[subscript d] values for Se(IV) and Se(VI) decreased significantly (P ≤ 0.001) with time during the anaerobic and subsequent aerobic phases. Applied Se(IV) fertilizer was rapidly removed (0 d = ~ 40% and 14 d ~100 %) into non-labile pools during the anaerobic phase, with no significant increase in the labile pool following short term aeration. The results suggest the rapid decrease in Se(IV) lability may be due to the strong non-reversible (at least for 7 days) sorption of Se (IV). In contrast, applied Se(VI) fertilizer was ~ 90 % labile at 0 d and decreased during the anaerobic phase to ~ 30% after 30d. There was no significant change in the lability of Se(VI) following the short term aerobic phase following anaerobic conditions. These results indicate that Se(IV) would not be an effective pre-plant fertilizer for rice production. Selenate is likely to be a more effective Se fertilizer, but losses to non-labile forms during the submerged phase of rice production may means that efficiency of pre-plant Se(VI) fertilization is also compromised.