Selenate redistribution during aging in different Chinese soils and the dominant influential factors

To date, few works have attempted to determine the effect of soil types on Selenium aging process and the possible influential factors. In this study, the differences in Se speciation distribution and availability in 15 Chinese typical agricultural soils were investigated using spiked selenate for the entire year. Results evidenced that after one year of incubation, Se transformed from soluble fraction to Fe/Mn oxides and organic matter bound fractions in neutral or alkaline soils (pH 7.09-8.51) and from exchangeable fraction to residual fraction in acidic soils (pH 4.89-6.82). The available Se content in all soils declined rapidly at the initial stage of aging, with most of the neutral or alkaline soils reaching equilibrium after 109 d, whereas the acidic soils reached equilibrium after only 33-56 d. The available Se content in soil decreased constantly during the entire aging process in S4 (Xinjiang Gray desert soil), S12 (Anhui Yellow brown earths), and S15 (Hunan Krasnozems). Elovich model was the best model (R² > 0.80) in describing the Se aging process. Estimated time for exogenous Se reaching the distribution of available Se in corresponding native soils extended from 9.7 y to 50.2 y, indicating a much longer time was required for spiked soil to reach equilibrium. Soil pH was the most significant factor directly and negatively influencing the aging process (p < 0.05), while organic matter played a dual role on Se speciation. Results could provide reference for the selection of unified equilibrium time on Se-spiked experiment.