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U.S. DEPARTMENT OF AGRICULTURE <br />NATURAL RESOURCES CONSEAVAiiON SERVICE <br />• PAGE 2 OF 2 • <br />04/26/00 <br />CHEMICAL PROPERTIES OF THE SOILS <br />Endnpte -- CHEMICAL PROPERTIES Of THE SOILS <br />this report shows estimates of some characteristics and features that affect soil behavior. <br />These estimates are given for the major layers of each soil in the survey area. the estimates <br />are based on field observations and on test data for these and similar soils. <br />CLAY as a soil separate consists of mineral soil particles that are less than 0.002 <br />millimeter in diameter. in this report, the estimated clay content of each major soil layer <br />is given as a percentage, by weight, of the soil material that is less than 2 millimeters in <br />diameter. The amount and kind of clay greatly affect the fertility and physical condition of <br />the sail. they determine the ability of the soil to adsorb cations and to retain moisture. <br />they influence shrink swell potential, permeability, and plasticity, the ease of soil <br />dispersion, and other sail properties. the amount and kind of clay in a soil also affect <br />tillage and earthmoving operations. <br />CATION EXCHANGE CAPACITY (CEC) is the total amount of cations held in a sail in such <br />a way that they can be removed only by exchanging with another cation in the natural sail <br />solution. CEC is a measure of the ability of a soil to retain calicos, same of which are <br />plant nutrients. Soils with low CEC hold few cations and may require more frequent <br />applications of fertilizers than soils with high CEC. Soils with high CEC have [he pptentia] <br />[p retain cations, thus reducing [he passibility of pollution cf ground water. <br />SOIL REACTION is a measure of acidity er alkalinity and is expressed as a range in pH <br />values. The range in pH of each major horizon is based on many field tests. For many soils, <br />values have been verified by laboratory analyses. Soil reaction rs important in selecting <br />:rops ar,d other plants, in evaluating soil amendments for fertility antl stabilization, and <br />in determining the risk of corrosion. <br />CALCIUM CARBONAiE is the percentage by weight of calcium carbonate in the fine earth <br />nateriai, less than 2 millimeters in size. <br />GYPSUM is the percentage by weight of hydrated calcium sulfates 20 millimeters or <br />smaller in size, in the soil. <br />SALINITY is a measure of soluble salts in the soil at saturation. It is expressed <br />as the electrical conductivity of the saturation extract, in millimhos per centimeter <br />at 2S degrees C. Estimates are based on field and laboratory measurements at representative <br />sites of nonirrigated soils. <br />the salinity of irrigated sails is affected by the quality of the irrigation water <br />and by the frequency of water application. Hence, the salinity of soils in individual fields <br />can differ greatly from the value given in the report. Salinity affects the suitability of <br />a soil for crap production, the stability of soil if used as construction material, and <br />the potential of the soil to corrode metal and concrete. <br />iCDIUM ADSORPTION RATIO (SAR) expresses the relative activity of sodium ions in <br />exchange reactions in the soil. SAA is a measure of the amount of sodium relative tc <br />.alcium and magnesium in the water extract frpr~ saturated soil paste. <br />