1999-04-21_PERMIT FILE - M1999024

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U. s. OEPARTHENT OF AGRICULTURE NATURAL~REsUURCEs CONSERVATION SERVICE Endnote -- PHYSICAL PROPERTIES OF SOILS C~ PHYSICAL PROPERTIES OF SOILS PAGE 2 OF 6 • OA/21/y8 This report shoos estimates of some characteristics and features that affect soil behavior. These estimates are given for the motor layers of each soil in the survey area. The estimates ere based an field observations and on test data for these and similar soils. CLAY as a soil separate consists of mineral soil Darticles that are less than O.OO't millimeter in diameter. in this report, the estimated clay content of each major soil layer is given es a percentage, by weight, of the soil material that is less then 't millimeters in diameter, The amount end kind of clay greatly affect the fertility and physical condition of the soil. They determine the ability of the soil to adsorb cations and to retain moisture. They influence shrink-swell potential, permeability, plasticity, the ease of soil dispersion, and other soil properties. The amount and kind of clay in a soil also affect tillage end earthmoving operations. HUIST BULk DENSITY is the vei4ht of soii (ovendryJ per unit volume. Volume is measured when the soil is et field moisture capacity, the moisture content at 1/3 bar moisture tension. Weight is determined after drying the soil at SOS degrees C. In this report, the estimated moist bulk density of each major soil horizon is expressed in prams per cubic centimeter of Soil material that is less then 2 millimeters in diameter. Bulk density data are used to compute shrink-svell potential, available eater capacity, total pore space, end other soil properties. The moist bulk density of a soil indicates the pore space available for eater and roots. A bulk density of more than 1.6 can restrict eater store4e and root Denetration. Hoist bulk density is influenced 6Y texture, kind or clay, content of organic matter, and soil structure. "rEkNEABILITY refers to the ability of a soil to transmit water ar air. The estimates indicate the rate of dovnvard movement of eater when the soil is saturated. Thar are based on soil characteristics observed in the field, particularly structure, porosity, and tetture. Permeability is considered in the design of soil drainage systems, septic tank absorption fields, end construction Where the rate of eater movement under saturated conditions affects behavior. AVAiLARLE WATEk CAPACITY refers to the quantity of eater that 'the soil is capable of storing for use by giants. She capacity for water storage is given in inches of water per inch of soil for each major sail layer. the capacity varies, depending on soii properties that affect the retention of eater and the depth of the root zone. The most important properties are the content of organic matter, soil teyture, bulk density, and soii structure. Available eater capacity is an important factor in the choice of giants or crops to be groan and in the design and management of irrigation systems. Available water capacity is not an estimate of the quantity of eater actually available to plants at any given time. SHRINk-SWELL POTENTIAL is the potential for volume change in a soii vith a loss or gain of moisture. Volume change occurs mainly because of the interaction of clay minerals with water and varies with the amount and type of clay minerals in the soil. The size of the load on the soil and the magnitude of the change in soil moisture content influence the amount of swelling of soils in place. Laboratory measurements of sueiling of undisturbed clods were made for many soils. For others, swelling vas estimated on 'the basis of the kind and amount of tier minerals in the soil and on measurements of similar soils. If the shrink-swell potential is rated moderate to very high, shrinking end sueiling can cause damage *.o buildings, roads, end other structures. Special design is often needed. Shrink-swell potential classes are based on the change in length of an unconfined clo6 as moisture content is increased trom air-dry to field capacity. The change is based on the soil fraction less than 't millimeters in diameter. The classes ere 'Lou,' a change of less then 3 percent; 'NOderaie,' 3 to 6 percent; end 'Hi4h,' more than 6 percent. 'Very high,' greater than Y percent, is sometimes used.