Retention of Cadmium by Several Soils of the Southeastern United States

Since significant entry of Cd into the food chain is undesirable, soil properties important in reducing plant availability of Cd must be identified. Solubility of applied Cd in various extraction solutions is one estimate of plant availability. Cadmium nitrate was applied at rates supplying up to 1.25 mmol Cd kg⁻¹ (140 mg kg⁻¹) to soil from the A horizons and some B horizons of 10 mineral and three organic soils. The treated soils were incubated at 20 °C and at the end of 2, 4, and 8 weeks samples were withdrawn and extracted with 1 M KCl, Mehlich 1 (M1), and 0.2 M (NH₄)₂C₂O₄ [AO]. Length of incubation had no effect on the quantity of Cd removed by the extractants (extractability). Extractability was related linearly to Cd application rate but the effect of soil type on slope (extractable Cd/applied Cd) was more pronounced with KCl (110% variation in slopes) and AO (270%) than with M1 (27%). At the 1.25 mmol Cd kg⁻¹ rate, KCl-extractable Cd decreased with increasing pH but differences among soils were large. Stepwise multiple regression was performed using sand; silt; clay; pH; cation exchange capacity (CEC); exchangeable cations; organic matter; dithionite-extractable Al and Fe; and AO-extractable Al, Fe, and Mn as independent variables. Exchangeable Ca and pH were important soil properties related to extractability with the three extractants but values of R² were < 0.8 even for three-variable models. Since pH was the dominant factor, the data were grouped into pH increments of 0.5 and regression repeated. Exchangeable Ca, CEC, and dithionite-extractable Al were important factors related to extractability, but values of R² were < 0.6. Overall, the ability to estimate extractability from basic soil properties was low. Paper no. 10852 of the Journal Series of the North Carolina Agric. Res. Service, Raleigh, NC. Research supported in part by funds from Fiber Industries, Inc., Charlotte, NC.