Response of corn to high levels of CuSO₄ and ZnSO₄ applications

Copper and Zn deficiencies of crop plants occur in various areas throughout the world. The sulfate forms of Cu and Zn are generally used to correct these micronutrient deficiencies. In agricultural practices, Cu and Zn are applied to soils not only as a fertilizer but also as manures, pesticides and waste materials such as sewage sludge. High levels of Cu and Zn application to agricultural soils are considered to pose a potential hazard to plants and animals. Research findings have not established Cu and Zn levels that either injure plants or increase Cu and Zn concentrations in edible plant portions to undesirably high levels. Published data on the fate of applied Cu and Zn indicate that there is little, if any, downward movement of these micronutrients in soils and that, with time, applied Cu and Zn revert to plant unavailable forms in soils.