The potential for potassium chloride fertiliser applications to leach cadmium from a grazed pasture soil

Abstract

Cadmium (Cd) is a biotoxic element that can enter the human food chain via plants grown in Cd-enriched soil. Chloride (Cl) can solubilise Cd in soil. Although fertilisers containing Cl are not recommended as they may increase plant uptake of Cd, potassium chloride (KCl) is regularly applied to replenish and maintain K in the soil of grazed pastures. A trial was conducted to see if an autumn application of low (0.02 mol L−1, equivalent to 30 kg K ha yr−1) or high (0.04 mol L−1) KCl and the same molar rates of CaCl2 (used as a check to other studies) would leach Cd over 4-months of normal (300-mm) or high (600-mm) autumn-winter rainfall without enriching Cd in plant shoots. Leaching losses of Cd were greater from the high KCl and CaCl2 treatments (1.80 and 1.70 g ha−1, respectively) than the low KCl treatment (1.27 g ha−1). All loads lost from the Cl treatments were greater than from the control treatment (0.53 g ha−1). Losses from Cl treatments represented 29–41% of the Cd applied in an annual application of 250 kg superphosphate ha−1. Pasture shoot Cd concentrations were not different to the control (mean = 0.088 mg kg−1). Applying Cl (e.g. as KCl) in autumn may be a simple strategy to help slow the enrichment of soil Cd and does not increase the uptake of Cd by pasture shoots.