Effect of Fertilizer Anions on the Solubility of Native and Applied Selenium in Soil

Abstract

AbstractSelenium (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.