Effect of Fertilizer Anions on the Solubility of Native and Applied Selenium in Soil
1973
Cary, E. E. | Gissel-Nielsen, G.
Selenium (Se) was added to the Madras sandy loam as K₂SeO₃ at rates of 0.02 and 0.5 ppm Se and as K₂SeO₄ at a rate of 0.02 ppm Se. Both Se sources were labeled with ⁷⁵Se. Combinations of nitrate, phosphate, and sulfate were added to the selenized Madras sl and to unselenized Madras sl and Dalton sil to determine what effect these fertilizer anions have on the solubility of applied and native Se as measured by extraction of Se with 0.01M CaCl₂. When selenate was added to the Madras sl, about 25% was fixed within 1.5 hours. After 73 days of equilibration with the soil, over 50% of the added ⁷⁵Se could be extracted with 0.01M CaCl₂. After an initial decrease during the first few hours, the specific activity of the CaCl₂ extracts remained nearly constant. Phosphate added with selenate had no effect on the extractability of ⁷⁵Se with 0.01M CaCl₂, but nitrate and sulfate slightly increased the amount of ⁷⁵Se extracted with 0.01M CaCl₂. Selenite reacted more completely with the soil than selenate during the same time. After 1.5 hours, only 9% to 17% of the ⁷⁵Se was extracted with 0.01M CaCl₂. After 73 days of soil contact about 3% of the ⁷⁵Se added as selenite was extracted with CaCl₂. The specific activity of the soil extracts was still decreasing after 73 days. The addition of phosphate with selenite increased the absolute amount of Se in the CaCl₂ extracts slightly. Nitrate and sulfate had no effect on the extraction of selenite-⁷⁵Se with CaCl₂ solution.
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