Cadmium phytoavailability in some New Zealand soils

The suitability of 8 common soil extractants to predict plant uptake of cadmium (Cd) from 10 New Zealand soils at low Cd concentrations was investigated in a glasshouse experiment. In addition, a study of Cd uptake by several vegetable, cereal, and pasture species in relation to different soil types was undertaken. The concentrations of Cd extracted from soils varied with each extractant: 0.05 M acid ammonium acetate-EDTA (pH 4.65) extracted the greatest concentration of Cd, whereas 0.01 M CaCl2 extracted the least. Results indicate that for all extractants tested, there were significant relationships between the concentration of Cd extracted and the concentration of Cd in plant material; however, the level of significance depended on the plant species and individual soil extractant. When all plants were considered together, it was found that 0.05 M Ca(NO3)(2) was the best predictor of plant Cd concentrations. Total Cd concentration was found to be the most important soil parameter influencing plant Cd concentrations. Plant Cd concentrations varied greatly among different plant species. The greatest uptake was found in lettuce and to a lesser extent carrot tops, and least in ryegrass, clover, and barley. All plants examined were within the maximum residue limit (MRL) in New Zealand for the Cd content of all foodstuffs intended for human consumption (i.e. 1 mg Cd/kg fresh weight).