PERMFILE47530 - Laserfiche WebLink

Home Browse Search

U.S. DEPARTMENi OF AGRICULTURE ~ AGE : OF 4 NATURAL RESDUACES CONSERVATION SERVICE 04/26/00 Endnote -- PHYSICAL PAOPERiiES OF SOILS PHYSICAL PROPERTIES OF SOILS this report shows estimates of some characteristics and features that affect soil behavior. these estimates are given for the major layers of each soil in the survey area. The estimates are based on field observations and on test data for these and similar sails. CLAY as a soil separate consists of mineral soil Darticles that are less than 0.002 millimeter in diameter. In this report, the estimated clay content of each major soil layer is oiven as a percentage, by weight, of the soil material that is less than 2 millimeters in diameter. the amount and kind of clay greatly affect the fertility and physical cmnditien 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 and earthmoving operations. NOISi BULK DENSITY is the weight of soil (mvendry) per unit volume. Volume is measured when the sail is 3t field moisture capacity, the moisture content at 1/3 bar moisture tension. Weight is determined after Trying the soil at l05 degrees C. In this report, the estimated moist bulk density of each major sail iorizmn is expressed in grams per cubic centimeter of sail material that is less than 2 millimeters in diameter. Bulk density data are used to compute shrink-swell potential, available water capacity, total yore space, and other soil properties. The moist bulk density of a soil indicates the pore space available for water and roots. A bulk density of more than l.6 can restrict water storage and ;oot per~etraticn. Moist sulk density is influenced by texture, kind of clay, content of organic matter, and soil structure. °ERMEABILIIY refers to the ability of a soil to transmit water or air. the estimates indicate the •ate of downward movement of water when the sail is saturated. They are based an soil characteristics observed in the field, particularly structure, porosity, and texture. Permeability is considered in She design of soil drainage systems, septic tank absorption fields, and construction where [he rate of rater movement under saturated conditions affects behavior. IVAILABLE WATER CAPACIi'! refers to the quantity of water that the soil is capable of storing for use by plants. the capacity for water storage is given in inches of water per inch of sail for each major soil layer. fhe capacity varies, depending on soil properties that affect the retention of water and the depth of the root !one. the most important properties are the content of organic matter, soil texture, bulk density, and sail structure. Available water capacity is an important factor in the choice of plants or crops to be grown and in the design and management of irrigation systems. Available water capacity is not an estimate of the quantity of +a ter actually available to plants at any given time. iHR]NK-SWELL POTENTIAL is the potential for volume change in a soil with a loss or gain of moisture. Volume :hange occurs mainly because of the interaction of clay minerals xith rater and varies with the amount and type ~f clay minerals in the soil. The size of the load on the soil and the magnitude of the change in soil moisture :ontent influence the amount of swelling of soils in place. Laboratory measurements of swelling of undisturbed :lolls were made for many soils. far others, swelling was estimated on the basis of the kind and amount of :lay minerals in the soil and on measurements of similar soils. If the shrink-swell potential is rated moderate to very high, shrinking and swelling can cause damage to buildings, roads, and other structures. Special design is often needed. Shrink-swell potential classes are based on the change in length of an unconfined clod as ooisture content is increased from air-dry to field capacity. the change is based on the soil fraction less ;han 2 millimeters in diameter. the classes are "Law," a change of less than 3 percent; "Moderate," 3 to 6 percent; and "High," more than b percent. "Very high," greater than 9 percent, is sometimes used.