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1 <br /> U.S. DEPARTMENT OF AGRICULTURE PAGE 2 OF 2 <br /> �URAL RESOURCES CONSERVATION SERVICE O1/28/97 <br /> ' CHEMICAL PROPERTIES OF THE SOILS <br /> note -- CHEMICAL PROPERTIES OF THE SOILS <br /> This report shows estimates of some characteristics and features that affect soil behavior. <br /> se estimates are given for the major Layers of each soil in the survey area. The estimates <br /> based on field observations and on test data for these and similar soils. <br /> �Y as a soil separate consists of mineral soil particles that are Less than 0.002 <br /> limeter 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 /> soil. They determine the ability of the soil to adsorb cations and to retain moisture. <br /> y influence shrink-swell potential, permeability, and plasticity, the ease of soil <br /> dispersion, and other soil properties. The amount and kind of clay in a soil also affect <br /> ILage and earthmoving operations. <br /> CATION EXCHANGE CAPACITY (CEC) is the total amount of cations held in a soil in such <br /> ay that they can be removed only by exchanging with another cation in the natural soil <br /> ution. CEC is a measure of the ability of a soil to retain cations, some of which are <br /> nt 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 the potential <br /> ' retain cations, thus reducing the possibility of pollution of ground water. <br /> SOIL REACTION is a measure of acidity or alkalinity and is expressed as a range in pH <br /> ues. The range in pH of each major horizon is based on many field tests. For many soils, <br /> ues have been verified by Laboratory analyses. Soil reaction is important in selecting <br /> crops and other plants, in evaluating soil amendments for fertility and stabilization, and <br /> determining the risk of corrosion. <br /> CIUM CARBONATE is the percentage by weight of calcium carbonate in the fine-earth <br /> material, less than 2 millimeters in size. <br /> ISUM is the percentage by weight of hydrated calcium sulfates 20 millimeters or <br /> smaller in size, in the soil. <br /> UNITY 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 25 degrees C. Estimates are based on field and laboratory measurements at representative <br /> Ies of nonirrigated soils. <br /> The salinity of irrigated soils is affected by the quality of the irrigation water <br /> by the frequency of water application. Hence, the salinity of soils in individual fields <br /> differ greatly from the value given in the report. Salinity affects the suitability of <br /> a soil for crop production, the stability of soil if used as construction material, and <br /> Jpotential of the soil to corrode metal and concrete. <br /> IUM ADSORPTION RATIO (SAR) expresses the relative activity of sodium ions in <br /> exchange reactions in the soil. SAR is a measure of the amount of sodium relative to <br /> t'cium and magnesium in the water extract from saturated soil paste. <br />