Additive copper-zinc interaction affects toxic response in soybean
Agricultural soils accumulate trace metals, particularly copper and zinc, as a result of their presence in wastes (sewage biosolids and manures) and fungicides that are applied over long periods of time. Regulations and guidelines for tolerable concentrations of these potentially plant-toxic elements in soils are based on the assumption that the toxic effects of the metals are substantially independent and not additive. However, additivity would imply that soil tolerance limits for each metal must be adjusted to compensate for the presence of another metal. There has been very little experimental work to date to provide a basis for determining the degree to which copper-zinc interaction in soils is additive as defined by the toxicity response in crops.