Effect of soil pH on cadmium phytoavailability in some New Zealand soils

The effect of soil pH on plant cadmium (Cd) concentrations was investigated in a glasshouse study, in conjunction with an evaluation of eight soil extractants as predictors of Cd concentrations in different plant species. Results showed that in general, increasing soil pH from 5.5 to 7.0 significantly decreased Cd concentrations in clover, lettuce, carrot, and ryegrass, and to a lesser extent in wheat, although the magnitude of the reduction varied between plant species and soil types. Soil extractants which were sensitive to soil pH e.g., 0.05M Ca(NO3)(2), 1M NH4Cl, and 0.05M CaCl2 or extract moderate amounts of Cd e.g., 1M NH4OAc and 0.04M EDTA were found to be the most effective in predicting plant Cd concentrations. Cd solubility as predicted using a semi-empirical equation which contained terms for pH, organic matter, and total Cd concentration was also found to be successful in estimating plant Cd concentrations for a number of plant species. It appears that pH may be a powerful tool in the management of plant Cd concentrations, however its true potential needs to be evaluated in a field situation.