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 ethylenediaminetetraacetic acid-extractable Zn concentration (7.3 mg kg-1). The addition of 5 to 20 kg Zn ha-1 decreased Cd concentrations in spinach leaves by 19 to 29 %, respectively. Cadmium concentrations in spinach roots decreased by up to 42 %. In contrast, the addition of Zn increased Zn concentrations in spinach roots and leaves by 86 % 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, and transport of Cd to the harvestable part of the plant. 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 (i.e. wheat), and the results confirmed in a field experiment.