Cadmium leaching from some New Zealand cropping soils

Mass balance modelling often shows that leaching is the main loss pathway for cadmium (Cd) from agricultural soils. There is however a scarcity of Cd leaching data measured under field conditions to support these modelled losses. This study used passive-wick fluxmeters installed at a depth of one metre at six commercial cropping sites to measure Cd in drainage over one year of monitoring. Cadmium concentrations were generally below the method detection limit (0.05 mu g Cd L-1) for all sites, with only the occasional detection from two sites and no detection from three other sites. The exception was site A where average Cd concentrations ranged from 0.06 to 0.18 mu g L-1 and the mean annual loss (+/- SE) was 0.33 +/- 0.08 g Cd ha(-1). This was similar to the amount estimated using the drainage flux multiplied by a modelled estimate of soil solution Cd concentrations for the site, 0.41 g Cd ha(-1). Cadmium balance models typically assess the rate of Cd accumulation in the 0-7.5 or 0-30 cm soil depth. Further studies are still required to obtain Cd leaching data collected under field conditions at these soil depths to allow modelled Cd leaching to be validated against measured data.