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restricted to poorly drained, very acid soils, soils derived from serpentine parent <br /> materials or soils that have been contaminated near smelters (Traynor, 1980; Munshower, <br /> 1983; and Barth et al ., 1981). Normal plant available nickel concentrations in soil are <br /> slightly less than 2 ppm (Barth et al ., 1981 ). <br /> Zinc. Zinc is a necessary component of several enzyme systems which regulate various <br /> metabolic activities within plants. Adequate zinc levels are essential for normal cell <br /> division, root growth, seed production, protein metabolism, and auxin formation (Tiedemann <br /> and Lopez, 1982). For normal growth, most plants generally require a minimum zinc <br /> concentration of 1 ppm while zinc related toxicity occurs at about 70 ppm. The potential <br /> for zinc deficiency is increased by many factors including but not limited to high pH, <br /> high lime rates, high phosphorous levels, and high concentrations of other metallic <br /> nutrients (Cu, Fe, and Mn). Zinc toxicity is more of a concern on acid soils because of <br /> the higher solubility of zinc on acid soils. The antidote for zinc toxicity is the <br /> application of lime (Traynor, 1980). <br /> Cadmium. Cadmium is a nonessential metallic element that is used in industry. Plant <br /> toxicities due to elevated levels of cadmium under natural conditions or in reclamation <br /> are unlikely (Barth et al ., 1981 and Munshower, 1983). <br /> Mercury. Mercury predominantly exists in an inorganic form which is not absorbed readily <br /> by plants. There have been no documented cases of mercury toxicity to plants or to <br /> animals under normal conditions. Mercury toxicity is limited to industrial or <br /> agricultural situations where mercuric fungicides or other contaminants are used. <br /> Lead. This is a non-essential (to plant and animal life) heavy metal that could induce <br /> plant toxicity symptoms if present in excess quantities. As the pH decreases, the <br /> solubility and the potential for lead toxicity increases. In most soils of the Great <br /> Plains, lead is complexed and not readily leached to ground water nor available for plant <br /> uptake (Barth et al ., 1981 and Munshower, 1983). <br /> Arsenic. Munshower (1983) states that toxic concentrations of arsenic in natural soils <br /> and overburden have never been reported. Barrett and others (1980) stipulate that <br /> toxicity is confined to soils which have accumulated arsenic through foliar spray <br /> compounds. The arsenates are fixed by soils in a relatively insoluble state and are not <br /> lost by leaching. The critical water-soluble arsenic concentration in soils is 2 ppm <br /> (USDA, 1957). <br /> 6-1-21 Revised 04/11/88 <br />