Cadmium Chemical Forms in Two Calcareous Soils Treated with Different Levels of Incubation Time and Moisture Regimes

Abstract

Sequential extraction is used effectively to determine the chemical forms of heavy metals. Since few studies have been conducted in calcareous soils of Iran, the current research has been carried out to evaluate the effect of moisture regimes and incubation time on the chemical forms of cadmium in two calcareous soils. Treatments included three levels of cadmium (0, 30 and 60 mg/kg of soil as CdSo4), three incubation times (2, 4 and 8 weeks), two soils (clay and sandy clay loam) and two moisture regimes (Water-logged and Field capacity). The experiment was performed as factorial on the basis of randomized complete blocks design with two replications. At 2, 4, and 8 weeks after treatment, the Tessier et al. (1979) sequential extraction method was applied to measure the cadmium concentration in water soluble-exchangeable (WsEx.), iron and manganese oxide (Fe-MnOx.), carbonate (Car.), organic matter (Om.) and residual forms (Res.). The results showed depending on the soil texture, 68 to 72 percent of the cadmium was in water soluble-exchangeable and iron-manganese oxide forms. Flooding condition decreased the concentration of cadmium in water soluble + exchangeable form and increased the concentration of cadmium in the forms of Fe-Mn oxides, carbonate and organic matter. Concentration of cadmium in residual form was higher in clay soil. In sandy clay loam soil, water soluble-exchangeable, carbonate and organic matter forms were higher than clay soil. The iron-manganese oxides form showed no significant difference in two soils at field capacity regime. In flooding conditions, the concentration of the water soluble-exchangeable form decreased and the concentration of other forms increased. In contrast to the oxidizing conditions at the reduction conditions, no significant difference was observed in the residual and organic matter forms in two soils.