Effect of straw amendment and plant growth on selenium transfer in a laboratory soil-plant system

Knowledge of the transfers of selenium (Se) in the soil-plant-atmosphere environmental compartments is fundamental in assessing Se cycling through the environment. The purpose of this study was to determine the effects of straw amendments and barley (Hordeum vulgare L.) on Se cycling in soils from Kesterson Reservoir, Merced County, CA (0.68 mg soluble Se kg(-1), 6.15 mg total Se kg(-1)), and to evaluate the feasibility of these agricultural practices as bioremediation strategies. Four treatments were evaluated: soil only, soil + straw, soil + plant, and soil + straw + plant. Straw amendments greatly reduced Se from soil solution (92-97% of initial soluble Se). Selenate [Se(VI)] was the predominant species in soil solution. Phosphate-extractable Se did not account for the decline in soluble Se. Selenium volatilized by microbes represented only 4-5% of the soluble Se removed. Highest Se removal from soil solution and highest Se volatilization rates occurred when both microbial activity and growth were maximal. Selenate microbial reduction to more insoluble Se forms is indicated as being responsible for this removal. Plants did not account for as much Se removal from soil solution as did straw amendments. Total shoot Se corresponded to 1-9% of soluble Se removal. At the end of the experiment, Se in plants represented 0.1-0.7% of total Se in the system, and the Se volatilized accounted for 0.2 to 0.5% of total Se inventory. The results obtained in this study suggest the use of straw amendments as a remediation technique for managing Se contamination at Kesterson Reservoir.