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Chemical Soil Properties- Ridgway Area, Colorado, Parts of Delta, Gunnison, <br />Montrose, and Ouray Counties <br />Chemical Soil Properties <br />This table shows estimates of some chemical characteristics and features that <br />affect soil behavior. These estimates are given for the layers of each soil in the <br />survey area. The estimates are based on field observations and on test data for <br />these and similar soils. <br />Depth to the upper and lower boundaries of each layer is indicated. <br />Cation - exchange capacity is the total amount of extractable cations that can be held <br />by the soil, expressed in terms of milliequivalents per 100 grams of soil at neutrality <br />(pH 7.0) or at some other stated pH value. Soils having a low cation - exchange <br />capacity hold fewer cations and may require more frequent applications of fertilizer <br />than soils having a high cation - exchange capacity. The ability to retain cations <br />reduces the hazard of ground -water pollution. <br />Effective cation - exchange capacity refers to the sum of extractable cations plus <br />aluminum expressed in terms of milliequivalents per 100 grams of soil. It is <br />determined for soils that have pH of less than 5.5. <br />Soil reaction is a measure of acidity or alkalinity. It is important in selecting crops <br />and other plants, in evaluating soil amendments for fertility and stabilization, and in <br />determining the risk of corrosion. <br />Calcium carbonate equivalent is the percent of carbonates, by weight, in the fraction <br />of the soil less than 2 millimeters in size. The availability of plant nutrients is <br />influenced by the amount of carbonates in the soil. <br />Gypsum is expressed as a percent, by weight, of hydrated calcium sulfates in the <br />fraction of the soil less than 20 millimeters in size. Gypsum is partially soluble in <br />water. Soils that have a high content of gypsum may collapse if the gypsum is <br />removed by percolating water. <br />Salinity is a measure of soluble salts in the soil at saturation. It is expressed as the <br />electrical conductivity of the saturation extract, in millimhos per centimeter at 25 <br />degrees C. Estimates are based on field and laboratory measurements at <br />representative sites of nonirrigated soils. The salinity of irrigated soils is affected <br />by the quality of the irrigation water and by the frequency of water application. <br />Hence, the salinity of soils in individual fields can differ greatly from the value given <br />in the table. Salinity affects the suitability of a soil for crop production, the stability <br />of soil if used as construction material, and the potential of the soil to corrode metal <br />and concrete. <br />Sodium adsorption ratio (SAR) is a measure of the amount of sodium (Na) relative <br />to calcium (Ca) and magnesium (Mg) in the water extract from saturated soil paste. <br />It is the ratio of the Na concentration divided by the square root of one -half of the <br />Ca + Mg concentration. Soils that have SAR values of 13 or more may be <br />characterized by an increased dispersion of organic matter and clay particles, <br />reduced saturated hydraulic conductivity and aeration, and a general degradation <br />of soil structure. <br />USDA Natural Resources Web Soil Survey <br />Conservation Service <br />National Cooperative Soil Survey <br />10/27/2012 <br />Page 1 of 18 <br />