Cadmium losses from a New Zealand Organic soil

Cadmium (Cd) losses from acidic Organic soils amended with phosphate fertiliser are potentially important for the assessment of Cd accumulation, but are currently poorly understood. This study investigated the effect of soil pH and single superphosphate (SSP) fertiliser at application rates of 0, 50, 100 and 200 kg P ha-1 on Cd leaching and plant uptake from an Organic soil in a lysimeter study. Average leaching losses ranged between 0.23 to 0.39 g ha-1. The greatest losses were from soils at pH 4.5 at the highest rates of P application (100 and 200 kg P ha-1). In comparison, there was no significant difference in the amounts of Cd lost at pH 5.5 or 6.5 at any rate of P application. Losses equated to <1% of the Cd added to the soil from an application of 200 kg P ha-1. Average ryegrass Cd concentrations ranged from 0.03 to 0.09 mg kg-1 dry weight. Soil pH had no significant effect on concentrations for the two lowest SSP application rates, whereas at the two high SSP treatments, Cd concentrations increased between pH 4.5 and 5.5, but decreased between pH 5.5 and 6.5. Cadmium losses from both leaching and plant uptake are low in this Organic soil, highlighting the important role organic matter and pH provide in retaining Cd.