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V. DEPARTMENT OP AGAICVLTVRE PAGE 2 OP <br />RESOURCES CONSERVATION SERVICE • OB/17/~ <br />1 <br />CHEMICAL PROPERTIES OF THE SOILS <br />E~o[e -- CHEMICAL PROPERTIES OF THH SOILS <br />T~ report shows ee[Sma[ea of some characteriet ica and features that of Eect soil behavior. <br />T e estimates are given for the major layers of each Boll !n the survey area. The estimates <br />a based on field observations and on teat data for these and similar soil e. <br />C ae a soil separate consists of mineral soil particles chat are lees Chan 0.001 <br />m imeter in diameter. In Chia report, the eetima tad clay content of each major soil layer <br />ie given ae a percentage, by weight, of the soil material that ie lees than 1 millimete ra in <br />diameter. The amount and kind of clay greatly affect the fertility and physical condition of <br />t~eoil. They determine the ability of the soil to adsorb cations and to retain moisture. <br />T 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 />[ age and ear[hmoving operations. <br />CON EXCHANGE CAPACITY (CEC) 1e the total amount of cations heltl in a Boil in such <br />a way [hat [hey can be removed only Dy exchanging with another cation In the natural eo it <br />s Lion. CEC ie a measure of [he ability of a soil to retain cations, some of which are <br />p~t nutrients. Soils with low CEC hold few cations and may require more frequent <br />app Stations of fertilizers than soils with high CEC. Soils with high CEC have [he potential <br />to retain cations, thus reducing the Poe eibility of pollution of ground water. <br />H~, REACTION ie a measure of acidity or alkalinity and ie exp reseed ae a range in pH <br />values. The range in pH of each major horizon ie based on many field [eats. Por many voile, <br />v ee have been verified by laboratory analyses. Soil reaceion ie important in selecting <br />c~e and other plants, in evaluating Boil amendments Eor fertility and stabilization, and <br />i etermining the risk of eorroeion. <br />IUM CARBONATE ie [he percentage by weight of calcium carbonate in the fine-ea r[h <br />~rial, lees Chan 1 mi llimetere in size. <br />GYPEUM ie the percentage by weight of hydrated talc Sum sulfates 10 millimeters or <br />e~ler Sn size, in the soil. <br />EALINITY is a measure of soluble salts in the soil at eaturat ion. It le exp ree sad <br />a the electrical conductivity of [he saturation extract, Sn millimhoe per centimeter <br />a~5 degrees C. Het imatee are Daeed on field ahd laboratory meaeuzeme n[e at representative <br />a e of non irrigated soils. <br />T eallnity oP irrigated soils ie affected by the quality of the irrigation water <br />a~ by [he frequency of water application. Hence, the eallnity of soils in individual fiel de <br />c differ greatly from the value given in the report. Salinity affects [he suitability of <br />a soil for crop production, the stability of aoil if used ae construction material, and <br />C' potential of the soil to corrode metal and concrete. <br />SODIUM ADSORPTION RATIO (SARI expresses [he relative activity of sodium lone Sn <br />exchange reactions in the Boil. SAR Se a measure of the amount of sodium relative Co <br />c~ium and magnesium in the water extract from saturated soil paste. <br />1 <br /> <br /> <br />