Can the application of zinc decrease cadmium concentrations in spinach in a zinc sufficient soil?

The application of zinc (Zn) fertiliser to soil has been proposed as a mitigation strategy to decrease plant cadmium (Cd) concentrations. The strategy is untested in New Zealand and it is unclear whether it is effective in soils that are not Zn deficient. We undertook a glasshouse experiment and measured what effect applying Zn had on Cd concentrations in spinach (Spinacia olearacea L.) cultivated in a soil with a high extractable Zn concentration (7.3 mg kg⁻¹) and total Cd concentration of 0.48 mg kg⁻¹. The addition of 5–20 kg Zn ha⁻¹ as zinc sulphate decreased Cd concentrations in spinach leaves after 64 days growth by 19–28% and in roots by up to 42%. In contrast, the addition of Zn increased Zn concentrations in spinach roots and leaves by 55% and 112% respectively. The decrease in Cd concentrations in spinach was likely a result of competition with Zn that restricted Cd uptake into the root. The results indicate there may be potential in using Zn fertiliser to decrease plant Cd concentrations. However, investigation needs to be undertaken to evaluate its effectiveness for soil types with different properties and Zn status, other food crops which may respond differently to spinach and the results confirmed in a field experiment. [ABSTRACT FROM AUTHOR]