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the United States (NRC 1979) . Zinc phytotox ici ty exists naturally 

 in only isolated instances with most toxicity problems related to 

 anthropogenic sources such as in metal mining, smelting and 

 refining . 



Zinc uptake by plants is influenced by the soil pH, soil 

 composition, CEC, organic matter, phosphorus levels, and soluble 

 zinc concentrations. Uptake is also influenced by the form of 

 zinc. Zinc oxides, carbonates, phosphates and sulfides are 

 generally less soluble and therefore less toxic than similar 

 concentrations of soluble zinc salts. Zinc availability to plants 

 is enhanced in low pH in soils where the solubility of many metals 

 is increased. The potential for zinc toxicosis is reduced in 

 soils high in calcium and magnesium and the increase of soil pH 

 from the liming of agricultural soils reduced zinc toxicosis (Lee 

 and Page 1967) . The fixation of zinc through microbial activity 

 also reduces zinc available for plant uptake. Studies suggest 

 plants remove 1 to 3 percent of the zinc added to a soil (Taylor 

 et al. 1982) . 



Absorption of zinc is influenced by copper, phosphorus, and 

 iron levels. Copper and zinc are antagonistic and the absorption 

 of one usually depresses absorption of the other. Phosphorus in 

 excessive amounts can reduce zinc uptake and, conversely, exces- 

 sive zinc apparently depresses phosphorus metabolism. Excess iron 

 tends to intensify a zinc deficiency. Translocation of zinc 



ccurs through the xylem (water transports system) and a small 

 amount may be redistributed via the phloem (food transport 

 system) . Normal zinc concentrations in plants range from 15 to 

 150 ppm (dry matter) with zinc toxicosis commonly occurring at 

 levels of 400 ppm (dry matter) (Gough et al. 1979). The suscepti- 

 bility of plants to zinc toxicity varies among species. Boawn and 

 Rasmussen (1971) have shown that monocotyledonous species (corn, 

 sorghum, barley and wheat) were more sensitive to excess zinc than 

 were dicotuledmons species (beans, peas, some leafy vegetables and 

 clover). Symptoms of zinc toxicity include stunted growth, 

 reduced yields, reduced size of leaves, necrosis of leaf tips and 



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