Effect of soil and foliar applications of zinc on cadmium concentration in wheat grain

Abstract

Summary. The effectiveness of foliar applications of zinc sulfate to decrease cadmium (Cd) concentration in wheat grain was assessed at 3 field sites in South Australia—Tumby Bay, Cummins and Keppoch. Foliar zinc (Zn) treatments were found to significantly (P<0.001) decrease Cd concentrations in grain at only 1 site, Tumby Bay. At this site the highest foliar Zn treatment (0.67 kg Zn/ha), which consisted of 2 applications of 0.33 kg Zn/ha applied early and late, decreased the mean Cd concentration in grain from 0.025 mg/kg for the nil treatment to 0.017 mg/kg. Timing of application of foliar Zn had no significant effect on Cd concentration in wheat grain. The effect of soil applications of zinc sulfate on grain Cd concentration was assessed at Tumby Bay only. There was no significant difference in grain Cd concentration between the soil Zn treatments. The results from this study suggested that the current recommended rates of foliar applications of Zn to ameliorate Zn deficiency are not high enough to decrease Cd concentration in wheat grain. This is most likely due to the recommended foliar rate of 0.33 kg Zn/ha not providing excess Zn to the plant such that there is enough Zn to be translocated to the root, which is the site of Cd uptake by the plant. The results suggest that the benefits of foliar Zn to minimise Cd concentration in grain are variable or that the rates used to correct Zn deficiency under field conditions are too low to decrease Cd uptake. Further work is required to distinguish between the 2 possibilities.