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Custom Soil Resource Report <br /> Soil chemical properties are measured or inferred from direct observations in the field <br /> or laboratory. Examples of soil chemical properties include pH, cation exchange <br /> capacity, calcium carbonate, gypsum, and electrical conductivity. <br /> Chemical Soil Properties <br /> This table shows estimates of some chemical characteristics and features that affect <br /> soil behavior.These estimates are given for the layers of each soil in the survey area. <br /> The estimates are based on field observations and on test data for these and similar <br /> 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 capacity <br /> hold fewer cations and may require more frequent applications of fertilizer than soils <br /> having a high cation-exchange capacity. The ability to retain cations reduces the <br /> 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 determined <br /> 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 <br /> 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 influenced <br /> 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 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 /> 47 <br />