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Custom Soil Resource Report <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 water. <br />Soils that have a high content of gypsum may collapse if the gypsum is removed by <br />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 by <br />the quality of the irrigation water and by the frequency of water application. Hence, <br />the salinity of soils in individual fields can differ greatly from the value given in the <br />table. Salinity affects-the suitability of a soil for crop production, the stability of soil if <br />used as construction material, and the potential of the soil to corrode metal and <br />concrete. <br />Sodium adsorption ratio (SAR) is a measure of the amount of sodium (Na) relative to <br />calcium (Ca) and magnesium (Mg) in the water extract from saturated soil paste. It is <br />the ratio of the Na concentration divided by the square root of one -half of the Ca + Mg <br />concentration. Soils that have SAR values of 13 or more may be characterized by an <br />increased dispersion of organic matter and clay particles, reduced saturated hydraulic <br />conductivity and aeration, and a general degradation of soil structure. <br />55 <br />