Slick Spots in Western Colorado Soils

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Compact impervious areas or "slick spots" frequently occur in the heavier-textured grey soils of Western Colorado. The assumption has been that the imperviousness of these areas is the result of sodium adsorption by the soil colloids. This assumption is strengthened by the fact that the slick spots are similar in textual grade to the adjoining productive areas but contain a higher percentage of sodium salts. However, in many of these impervious soils, when replaceable sodium is determined by the usual procedure of first, washing to remove readily soluble electrolytes and then treating the washed soil with ammonium salt, the replaceable sodium found is only a small fraction of the base exchange capacity. <br> Furthermore, many of the slick spots contain a high percentage of calcium sulfate vvhich might be expected to keep sodium adsorption relatively low, and no doubt would do so, except for the low solubility of calcium sulfate compared with sodium salts. Because of the low solubility of calcium sulfate, the calcium would be precipitated in the soil as the moisture decreased, thus preventing an increasing concentration of this ion. At the same time, the sodium ion concentration would increase with decreasing~ moisture to a point probably sufficient to result in a high percentage of replaceable sodium in the colloids. In this case the high concentration of electrolytes should prevent deflocculation, even though the soil was high in adsorbed sodium. It is clear, then, that if we are to accept the hypothesis that the slick spots are the result of sodium adsorption, it also is necessary to assume as corollaries that this adsorption occurs in the presence of an excess of calcium sulfate and that the properties of a sodium soil may render it less pervious than a calcium soil, even in the presence of enough electrolytes to cause flocculation. This paper is a study of these assumptions.

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ELECTRONIC FILE - BOTANY: OTHER <br>
Robert Gardner, Robert S. Whitney. Alvin Kezer. 1937. Slick Spots in Western Colorado Soils. Colorado State College, Colorado Experiment Station, Fort Collins, Colorado. Technical Bulletin 20. 17 pp.