1999-03-08_PERMIT FILE - M1999025

Home Browse Search

U DEPARTMENT OP ACRICVLTVRE PACE 2 OP 4 N RESnURCES CONSERVATION SERVICE . • OB/17/98 B~ote -- PHYSICAL PROPERTI EE OP SOILS PHYSICAL PROPERTIEE OP SOILS T report shows set imatee of some characterist ice and features [ha[ affect Boil behavior. These set imates given for the major Jaye re of each soil in the survey area. The estimates are based on field oboe rvatione on teat data for these and similar soils. C ae a so it saps rate consists of mineral eo it part sties Chat are less than 0.002 millimeter in diameter. I hie report, the set imated clay content of each major eo it layer ie given ae a percentage, by weight, of the eo 1 material [hat Se less than 2 millimeters in diameter. The amount and kind of clay greatly affect the fertility and phys Lcal condition of the soil. They determine the ability of the soil to adsorb cations and t stain moisture. They influence shrink-swell potential, perms aD ility, plasticity, Che ease of soil ereion, and other Boll properties. The amount and kind of clay in a Boil also affect tillage and earthmovi ng operations. M T BULR DENSITY ie Che weight of soil (ovendry) per unit volume. Volume Se measured when the aoil ie a said moisture capacity, the moisture cone nt at 1/] bar moisture [ens ion. Weight is determined of car drying [he soil a[ 105 degrees C. In Chie report. [he set ima[ed moist bulk density o£ each major sc it h~zon ie exp re seed Sn grams per cubic centimeter of Boil material the[ Se less than 2 millimeters in d star. Bulk dens icy data are used to compute shrink-swell potential, available water capacity, total pore apace, and other soil properties. The mote[ bulk density of a soil indicates the pore apace available for water and roots. A bulk de nasty of more Chan 1.6 can restrict water eto rage and root penetration. Moist b~ density is influenced by texture, kind of clay, content of organic matter, and soil structure. PERMEABILITY refers to the ability of a Boil [o [ra nemit water or air. The eat imaCes indicate the r of downward movement of water when the soil ie ea[ura[e d. They are ba eed on soil characterie[ics o rved in the field, particularly structure, porosity, and texture. Permeability ie coneide red in t design of soil drainage systems, wept is tank absorption Eielde, and construction where the race of water movement under saturated conditions affects behavior. A~LABLE WATER CAPACITY ref ei9 to Che quantity of water that Che soil ie capable of storing for use by p [e. The capacity fox water storage ie given in inches of water per Snch of soil Eor each major soil layer. The capacity varies, depending on so it props roes chat affect the retention of water and [he depth of [he root ¢~ The moat important properties are [he content of organic metre r, soil texture, bulk density, and soil e Cure. Available water capacity Se an important factor in the choice of plants or trope [o be grown and in the design and management of irrigation systems. Available water capacity ie not an set imate of [he quantity of water actually available to plants a[ any given time. E ~NE-SwBLL POTENTIAL ie the potential Ear volume change in a soil with a lose or gain of moisture. Volume change occurs mainly because of the interaction of clay minerals with water and varies with the amount and type o lay mine role Sn the eo il. The size of the load on the Boll and the magnitude of the change in eo it moisture cent influence the amount of swelling of soils in place. Laboratory meaeureme me of swelling of undisturbed c e were made Eor many voile. Por others, swelling was estimated on the basis of the kind and amount of clay minerals in Che Boil and on meaeuremente of similar soils. If [he shrink-swell potential ie rated moderate [ ery high, shrinking and swelling can cause da mega to builds vge, roads, and other st ructuree. Special design i ften needed. Shrink-swell potential classes are Daeed on the change in length of an unconfined clod ae mo store Content Se Snczeaeed from air-dry to field capacity. The change ie based on the soil fraction lees Chan 2 millimeters in diameter. She classes are •LOW,• a change of lees than ] percent; 'Moderate,' 3 to 6 pent: and 'High,' more than 6 percent. 'Very high,' greater than 9 percent, ie sometimes used.