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UU. UEYitATNENl Ut AUa1000lUat rout t vt t <br />NATURAL RESOURCES CONSERVATION SERVICE • II/tl/98• <br />CHEMICAL PROPERTIES OF THE SOILS <br />Endnote -- CBENICAL PIOPERTIES OF TSE SOILS <br />This report ahora eatiutea of some chuacteriatica and featarea that affect soil behnior. <br />These eatiuta are giren for the major lgera of etch soil im the auney tree. The eatiuta <br />are based om field obeervatimma amd on teat data for these sad similar soils. <br />CLAY as a soil aepante camaiata of mineral soil particles that are leas than 0.002 <br />millimeter in diameter. In this report, the estimated clay content of euh ajar soil layer <br />is given as a percentage, by refight, of the soil uterial that is leas lham 1 millimeter in <br />diameter. The amommt and hind of clay greatly affect the fertility and physical condition of <br />the soil. They determine the ability mf the coil to adsorb cations and to retain moisture. <br />They inflmemce ahrimh-erell potential, permeability, and plasticity, the ease of soil <br />dispersion, and other soil properties. The amount and hind of clay in a eoil also affect <br />tillage and arthmoring opertions. <br />CATION ERCHANGE CAPACITY (CEC is the total amount of cations held in a soil in such <br />a ray that they cam 6e removed only by erchanging rich another catimn in the natural soil <br />solution. CEC is a measure of the ability of a soil to retain cations, some of rhich are <br />plant mutriemta. Soils rich for CEC 6mld ter cations and say require more frequent <br />applications of fertilizers than sm;ls rith high CEC. Soils rich high CEC have the potential <br />:o retain cations, thus reducing the possibility of pollution of ground rater. <br />;OIL REACTION is a measure of acidity or alkalinity and is eroressed as a ranee in off <br />+slues. the range in pH of each major horizon is based on many field !ants. For many sails. <br />+alues have been verified by (aboratory analyses. Soil reaction is important in selectin¢ <br />.rope and other pleats, in evaluating soil amendments for fertility and stabilization, and <br />n determining the risk of corrosion. <br />~A'.^IUM CARBONATE is the percentage by refight of calcium carbonate in [he tine-earth <br />raterial, less thao 1 millimeters in size. <br />IyPSUM is the percentage by refight of hydrated calcium sulfates t0 millimeters or <br />s*.aller in size, in the soil. <br />1LINITY is a measure of soluble salts in [he soil at saturation. It is erpressed <br />s the electrical conductivity of the saturation ertract, in millimhos per centimeter <br />:: 1S degrees C. Estimates are based on field and laboratory measurements at representative <br />.:es of nonirrigated sails. <br />e salinity of irrigated soils is affected ty the quality of [he irrigation rater <br />:-.d by the frequency of rater application. Hence, the salinity of soils in individual fields <br />an differ greatly from the value ¢iven in the report. Salinity affects the suitability of <br />:soil for crop production, the stability of soil if used as construction material. and <br />ne potential mf the soil to corrode metal and concrete. <br />;ODIUM ADSORPTION RATIO ISARI ermresses the relative activity of sodium ions in <br />erchange reactions in [he soil. SAR is a measure of the amount of sodiun relative to <br />.alcium and magnesium in the mater ertract from saturated soil paste. <br />