Plant accumulation of cobalt from soils with artifically elevated cobalt levels

Abstract

Three soils and 10 plant species were utilized to determine levels of plant accumulation of cobalt, sorption of cobalt in soil, influence of three management techniques on cobalt availability, and evaluation of four extractions as availability indicies (2.5% acetic acid, 0.01 M EDTA, DTPA-TEA, and total). Acidic Marietta loam sorbed approximately 2 1/2 times less cobalt than calcareous Norwood silt loam. It is suggested that CaCO(,3) complexes and/or precipitates cobalt. This was further shown in greenhouse growth trials where at equally elevated levels of soil cobalt, tall fescue grown in Marietta soil accumulated twice the cobalt as that grown in Norwood soil. Further, adding agricultural lime to both soils at 400 mg Co kg('-1) decreased tall fescue accumulation of cobalt, with plants grown in Marietta soil showing the greatest decrease. Addition of MnO(,2) at varying levels to Marietta and Norwood soils containing 400 mg Co kg('-1) failed to decrease tall fescue accumulation of cobalt. Layering 6 cm uncontaminated soil over 400 mg Co kg('-1) Marietta and Norwood soil effectively doubled cobalt accumulation by tall fescue. This would appear to be due to healthy vigorously growing roots encountering the elevated soil cobalt as opposed to having to develop in the higher cobalt levels. Cobalt aged in a Providence soil (cobalt added as a component of a petroleum waste sludge) was less available to tall fescue than cobalt freshly added to uncontaminated Providence soil. Effects of the waste can not be partitioned out. Grasses grew best, followed by vegetables, and the poorest growth was exhibited by legumes. Warm season grasses accumulated the lowest quantity of cobalt. Vegetables, legumes, and cool season grasses accumulated similar amounts of cobalt. The four cobalt extractions utilized did not appear to differ in their ability to predict plant accumulation. Total cobalt determinations were as good if not slightly better in their R-square values and ability to predict plant accumulation as the three extracting solutions (2.5% acetic acid, 0.01 M EDTA, and DTPA-TEA). Acetic acid extractable cobalt generally explained the lowest amount of variation (lower R-square values) in plant cobalt accumulation.