Can the application of farm dairy effluent enhance cadmium leaching from soil?

The application of amendments such as farm dairy effluent (FDE) to soils which contain dissolved organic carbon (DOC) has the potential to increase cadmium (Cd) leaching through the formation of soluble organo-Cd complexes. However, the extent of Cd leaching loss is currently unknown. A lysimeter study measured Cd leaching from coarse and fine-textured Pumice soils amended with either FDE or single superphosphate (SSP) fertilizer. Results showed that despite FDE having a DOC concentration of 3000 mg L−1, concentrations in drainage were low (7.2 to 14.6 mg DOC L−1), probably reduced by microbes and/or sorption onto iron and aluminium oxides in the soil. As a result, there was no significant difference in the amount of Cd lost from the soil amended with FDE (0.79 g ha−1) or SSP (0.70 g ha−1). In comparison, greater amounts of Cd were lost from the fine-textured (0.92 g ha−1) than from the coarse-textured soil (0.57 g ha−1), primarily due to significantly higher Cd concentrations in drainage. The study indicates that a one-off application of FDE at the maximum rate allowed by regulators is unlikely to affect Cd leaching losses, although this still should be confirmed for other soil types that receive FDE.