Cadmium forms and plant availability in compost-amended soil

Organic matter amendments to metal-contaminated soil can have an ameliorative effect due to increased surface area and an increase in the number of specific adsorption sites. A greenhouse experiment was conducted where composted biosolids were added at 0, 100, and 300 tons ha(-1) and a Cd salt was added at 0, 5, 10, 20, and 50 mg kg(-1) to a Southeastern Piedmont soil. Corn (Zea mays L.) was grown for 42 days and plant weights and cadmium (Cd) content was measured. Soil Cd was extracted according to a sequential fractionation procedure to extract operationally-defined forms of the metal. The CEC of the soil and the organic matter content increased with biosolid additions, but soil pH remained stable. Phytotoxicity was greatly reduced by addition of biosolids, especially at the medium rate of 10 mg kg Cadmium content of the plants was decreased from 105 to 30 mg kg(-1) by the biosolid additions at the 10 mg Cd kg(-1) rate. The decrease in phytotoxicity and in plant Cd was attributed to a redistribution of Cd from the water soluble and exchangeable fractions to the organic fraction, which decreased the plant availability. The results of this study indicate that composted biosolid amendments can be useful in decreasing Cd uptake by plants from contaminated soil and may bring about an increase in plant growth.