Mitigating Cadmium Accumulation in Spinach and Onions by the Application of Silicon Fertilizer to Soil

Cadmium (Cd) is readily absorbed by plants and can accumulate to concentrations that exceed food standards. Testing strategies that can mitigate plant uptake of Cd are essential to help manage the risk to food quality. We measured whether applying silicon (Si) fertilizer to a soil contaminated with Cd from phosphate fertilizer could decrease Cd concentrations in spinach (Spinacia olearacea) and onion (Allium cepa). The application of Si (1000 and 2500 kg ha(-1)) increased spinach dry matter (DM) yield and Si concentrations but had no effect on plant Cd concentrations or uptake. Application of Si had no effect on DM yield or Si concentrations in onions, but there was a 45% decrease in Cd concentrations in the onion bulb. Application of Si had no effect on calcium nitrate-extractable Cd. The decrease in Cd concentrations in onions was likely related to Si restricting the movement of Cd from the root to the harvestable part of the plant. These findings indicate that Si may have some potential as a mitigation tool to decrease plant uptake of Cd. Further investigation is required to evaluate its effectiveness across different soil types and test the response of a wider range of crops under field conditions.