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Chemical Soil Properties <br />This table shows estimates of some chemical characteristics and features that affect soil behavior. These estimates are given for the layers of <br />each soil in the survey area. The estimates are based on field observations and on test data for 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 extactable bases that can be held by the soil, expressed in terms of milliequivalents per 100 <br />grams of soil at neutrality (pH 1.0) or al some other slated pH value. Soils having a low cation-exchange capacity hold fewer cations and may require <br />more frequent applications of fertilizer than soils having a high cation-exchange capacity. The ability to retain cations reduces the hazard of <br />ground-water pollution, <br />"Effective cation-exchange capacity" refers to the sum of extractable bases plus aluminum expressed in terms of milliequivalents per 100 grams of <br />soil. It is delertnined 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 and other plants, in evaluating soil amendments for fertility and <br />stabilization, and in determining the risk of corrosion. <br />"Calcium carbonate" equivalent is the percent of carbonates, by weight, in the fraction of the soil less than 2 millimeters in size. The availability of <br />plant nutrients is influenced by the amount of carbonates in the soil. Incorporating nitrogen fertilizer into calcareous soils helps to prevent nivite <br />accumulation and ammonium-N volatilization. <br />"Gypsum' is expressed as a percent, by weight, of hydrated calcium sulfates in the fraction of the soil less than 20 millimeters in size. Gypsum is <br />partially soluble in water. Soils that have a high content of gypsum may collapse if the gypsum is removed by perwlating water. <br />'Salinity" is a measure of soluble salts in the soil at saturation. It is expressed as the elecOrical conductivity of the saturation extract, in millimhos <br />per centimeter at 25 degrees C, Estimates are based on field and laboratory measurements at representative sites of nonirtigated soils. The salinity of <br />irrigated soils is affected by the quality of the irrigation water and by the frequency of water application. Hence, the salinity of soils in individual fields <br />ran differ greatly from the value given in the table. Salinity affects the suitability of a soil for crop production, the stability of soil if used as construction <br />material, and the potential of the soil to tartaric metal and concrete. <br />"Sodium adsorption ratio' (SAR) is a measure of the amount of sodium (Na) relative to calcium (Ca) and magnesium (Mg) in the water extract from <br />saturated soil paste. It is the ratio of the Na concenVation divided by the square root of one-half of the Ca + Mg concentration. Soils that have SAR <br />values of 13 or more may be characterized by an increased dispersion of organic matter and clay particles, reduced saturated hydraulic conductivity <br />and aeration, and a general degradation of soil structure. <br />RECEIVED <br />FEB 1 6 2001 <br />Division of Reclamation, <br />Mining and Safety <br />USDA Natural Resources Tabular Data version:4 <br />Couservatioa Service Tabular Data Version Date: 12/1512005 Page 2 of 2 <br />