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cadmium (Lund et al . 1981). In areas where soils have been 

 contaminated, soil concentrations may approach 1000 ppm, and 

 plants may accumulate cadmium to levels in excess to 200 ppm, (dry 

 weight), depending on the species (Kabata-Pendi as and Pendias 

 1984). In contaminated soils the highest cadmium concentrations 

 are found in surface layers and decrease rapidly with depth, due 

 to the low mobility of this element. Total soil cadmium levels 

 are not good indices of the availability of the element to the 

 plant, as much of the total cadmium in soil may be bound in 

 compounds of low solubility (Pickering 1980). 



Cadmium, like many metals, is more mobile and thus more 

 available to plants in soils of low pH (4.5 to 5.5). Alkaline 

 soils exhibit low cadmium mobility, and decrease the risk of plant 

 toxicity even in heavily contaminated soils ( Kabata-Pendias and 

 Pensias 1984). It has been shown, however, that whereas the 

 availability of cadmium for plant uptake is decreased by liming, 

 cadmium added to the soil does result in increased uptake by 

 plants (Baker et al . 1979). 



Chang et al . (1982) found that the uptake of cadmium and zinc 

 in barley cultivars was more influenced by the soil type (and pH) 

 than by the specific barley cultivar. Similar findings by White 

 and Chaney (1980) indicated that soil types strongly influence 

 zinc, cadmium and manganese uptake in soybeans and that organic 

 matter was more effective than hydrous oxides of iron and manga- 

 nese in moderating the uptake of excessive soil heavy metals. A 

 study by Haghiri (1974) suggested that the soil cation exchange 

 capacity (CEC) largely determined the uptake of cadmium in oat 

 shoots and that organic matter had little effect on the uptake of 

 this element other than increasing the CEC. The study found that 

 the concentration of cadmium in soybean shoots increased with in- 

 creasing soil temperature. Chaney et al . (1976) revealed that 

 increased levels of soil zinc increased cadmium uptake by soy- 

 beans. Boggess et al . (1978) reported that significant differ- 

 ences existed in the susceptibility of soybeans to cadmium among 

 several varieties tested. These authors found that the observed 

 susceptibility was due more to plant uptake characteristics than 



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