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<br /> <br />• <br />Z'mc. Zinc is a necessary component of several enzyme systems which regulate various metabolic <br />activities within plants. Adequate zinc levels are essential for normal cell division, root growth, seed <br />production, protein metabolism, and auxin formation (Tiedemann and Lopez, 1982). For normal <br />growth, most plants generally require a minimum zinc concentration of 1 ppm while zinc related <br />toxicity occurs at about 70 ppm. The potential for zinc deficiency is increased by many factors <br />including but not limited to high pH, high lime rates, high phosphorous levels, and high concentrations <br />of other metallic nutrients (Cu, Fe, and Mn). Zinc toxicity is more of a concern on acid soils because <br />of the higher solubility of zinc on acid soils. The antidote for zinc toxicity is the application of lime <br />(Traynor, 1980). <br />Cadmium. Cadmium is anon-essential metallic element that is used in industry. Plant toxicities due <br />to elevated levels of cadmium under natural conditions or in reclamation are unlikely (Barth et al., <br />1981 and Munshower, 1983). <br />Mercury. Mercury predominantly exists in an inorganic form which is not absorbed readily 6y plants. <br />There have been no documented cases of mercury toxicity to plants or to animals under normal <br />conditions. Mercury toxicity is limited to industrial or agricultural situations where mercuric fungicides <br />or other contaminants are used. <br />Lead. This is anon-essential (to plant and animal life) heavy metal that could induce plant toxicity <br />symptoms if present in excess quantities. As the pH decreases, the solubility and the potential for <br />lead toxicity increases. In most soils of the Great Plains, lead is complexed and not readily leached <br />to ground water nor available for plant uptake (Barth et al., 1981 and Munshower, 1983). <br />enic. Munshower (1983) states that toxic concentrations of arsenic in natural soils and <br />overburden have never been reported. Barrett and others (1980) stipulate that toxicity is confined <br />to soils which have accumulated arsenic through foliar spray compounds. The arsenates are fixed <br />by soils in a relatively insoluble state and are not lost by leaching. The critical water-soluble arsenic <br />concentration in soils is 2 ppm (USDA, 1957). <br />Revised 9/99 2.04.6-18 <br />