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31 • <br />Boron and cadmium are examples of potentially toxic trace elements that <br />vary in solubility >n soil water as a function of pH. In the naturally <br />neutral to alkaline arid high plains soils, these and similar elements <br />are relatively immobile and do not comprise much of a hazard to grazing <br />animals. However, addition of fertilizers and other soil-building sub- <br />stances and addition of moisture in excess of that found in nature changes <br />the leaching rates, the hydrogen ion concentrations, and the characteris- <br />tics of soil profile development such that elemental mobility can be <br />greatly increased and potentially toxic plants can result. For this rea- <br />son, soil chemistry should be well understood before a reclamation plan <br />is developed. Soil acidification can occur in manners that would not be <br />readily predictable and can have significant effects upon future soil <br />fertility and productivity. For instance, interaction between nitrogen <br />fertilizers and nitrogenous soil bacteria {Nitrosomonas spp. and Nitrobacter <br />spp.) can result in production of a great excess of hydrogen ions which, in <br />neutral or alkaline soil conditions, may force release of available nutrient <br />cations such as calcium, magnesium, and potassium from their storage sites <br />in clay minerals. While this may greatly stimulate <br />plants growing on such a soil when it occurs, unless those plants can make <br />use of all the nutrients thus released and provide organic litter for <br />their further storage upon decomposition of the seasonal vegetation, then <br />much of the nutrient capital of the soil will be depleted and either washed <br />away or blown away, or carried beyond the reach of plants through <br />