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.
