madison, wi, november 9, 2009 -- agricultural soils accumulate（积聚，堆积） trace metals（微量重金属）, particularly 1 and 2（锌）, as a result of their presence in wastes (sewage脏水，污水 biosolids生物固体 and manures肥料) and fungicides（杀菌剂） that are 3 over long periods of time. regulations and guidelines for tolerable（可容忍的，可以的） concentrations of these potentially plant-4 elements in soils are based on the assumption that the toxic effects of the metals are substantially independent and not 5. however, additivity would imply that soil 6 limits for each metal must be adjusted to 7 for（补偿，赔偿） 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 8（毒性） response in crops. researchers at cornell university have investigated the copper-zinc interaction in two soils with different 10, using soybean growth and metal uptake into leaves to evaluate both toxicity and availability of these metals to the plants. soybean crops were grown in pots in the field in two successive years after allowing copper and zinc sulfate（硫酸锌）-amended soils to age in the field for one year prior to the first planting. copper and zinc were added to individual soils to provide 0, 50,100, 200, and 400 mg/kg of each metal as well as every possible combination of addition levels of the two metals. the results from the study are published in the november-december issue of journal of environmental quality.
11 effects of copper and zinc were observed both in the soil as well as in the soybean toxic response. in the soil, high copper had a strong effect on 12 zinc adsorption（吸附） on soil particles, 13 causing zinc to be more easily extractable（可抽出的） and available. conversely, there was only a moderate interactive effect of zinc on copper adsorption, probably explained by the higher 14（密切关系，吸引力） of copper for soil adsorption sites, particularly those associated with organic matter.
the toxic effects of copper and zinc on soybean growth was found to be additive to a large degree, as measures of both extractable copper and zinc in the soils were needed to adequately explain the inhibition of plant growth over all treatments. however, the toxic effect of copper was stronger than that of zinc, possibly explained by the observed severe impact of copper on soybean root development. soil 9 had a marked influence on the degree of copper and zinc toxicity and availability to soybeans, consistent with numerous studies that have shown coarse-textured soils to be more 15 to（对……敏感的） the toxic effects of heavy metals on crops.
the results from the study indicate that guidelines for tolerable upper limits of copper and zinc concentrations in soils are likely to require allowance for the presence of a second toxic metal at elevated concentrations, which could lower the tolerable limit for either copper or zinc. furthermore, tolerable limits for copper and zinc in soils are likely to be lower in coarse-textured soils.
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