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3.4 Zinc in soils and plants 



3.4.1 Zinc literature review 



Zinc is an essential plant nutrient normally present in soils 

 at a concentration of 10 to 300 pptn and averages 54 ppm in U.S. 

 soils (Connor and Shacklette 1975). Typical levels in vegetation 

 range from 25 to 150 ppm (dry wt . ) . Most research concerning zinc 

 in soils and plants has examined the phenomenom of zinc defi- 

 ciency. Zinc toxicity is rare, usually only occurring in contami- 

 nated areas or in extremely acid soils. High levels of soil 

 calcium and phosphorus, and alkaline soil conditions reduce zinc 

 availability to plants, lowering the risk of plant toxicity even 

 in zinc-contaminated soils (Kabata-Pendias and Pendias 1984). 

 Plant uptake of zinc is also influenced by the organic matter 

 content of the soil, presence of chelating compounds, and overall 

 soil fertility (Shuman 1980). Plant species vary widely in their 

 tolerance to zinc which further complicates efforts to determine 

 specific levels of phytotoxici ty (Taylor et al . 1982). Studies 

 examining the relationship between zinc concentrations in soil and 

 plant tissue with zinc phytotoxicity are summarized in Tables 42, 

 43 and 44. 



3.4.2 Zinc in soils 



3.4.2.1 Total zinc in soils 



Total soil zinc concentrations in excess of 600 ppm were 

 generally associated with yield reductions greater than 25 percent 

 in most crop species (Table 42). The only exception found in the 

 reviewed literature was the sludge study by Hinesly et al . (1982) 

 which noted no yield reductions for corn at a total soil zinc 

 concentration of 606 ppm. The application of sludge study results 

 should be used with extreme caution due to the ameliorating effect 

 of sludge. Yield reductions in the 500 to 600 ppm total soil zinc 

 range were between 8 percent found for peas and potatoes (Boawn 

 and Rasmussen 1971) and 72 percent found for soybeans (White and 



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