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swelling. Septic tank absorption fields of conventional size do not function adequately <br /> because of the slow permeability of the soil. Other kinks of sewage disposal systems <br /> may be needed. Preserving the existing plant cover during construction helps to control <br /> erosion. This map unit is in capability subclass Vie, non-irrigated. It is 60 percent Salt <br /> Flat #34 range site and 40 percent Shaly Plains#46 range site. <br /> 67- Manvel silty clay loam, saline. Tis deep, moderately well drained soil is on stream <br /> terraces and swales. It formed in alluvium derived dominantly from limestone and <br /> shale. Slope is 1 to 3 percent. The native vegetation is mainly grasses. Elevation is <br /> 5,000 to 5,400 feet. The average annual precipitation is 12 to 14 inches, the average <br /> annual air temperature is 51 to 53 degrees F, and the average frost-free period is 160 to <br /> 170 days. Typically, the soil is silty clay loam about 30 inches thick over silt loam to a <br /> depth of 60 inches or more. The soil is moderately alkaline and saline. Included in this <br /> unit is an area in the southwest corner of Sec. 6, T. 195., R. 68 W., adjacent to the Brush <br /> Hollow Creek drainageway, of very poorly drained soils. The high-water table is caused <br /> by seepage of irrigation water. Steepness of slope is about 3 to 6 percent, and the <br /> vegetation is typical of saline meadow areas. Permeability of this Manvel soil is <br /> moderate or moderately slow. Available water capacity is moderate. Effective rooting <br /> depth is 60 inches or more. Runoff is slow, and the hazard of water erosion is slight to <br /> moderate. In most areas the upper soil is moderately saline. In a few areas, the upper <br /> soil is slightly saline. The salinity of the root zone can be reduced significantly where <br /> irrigated. This unit is use mainly for rangeland. It is also used for irrigated hayland and <br /> pastureland. Alfalfa or a mixture of grass and alfalfa are commonly grown. The <br /> potential plant community on this unit is mainly alkali sacaton, blue grama, western <br /> wheatgrass, and fourwing saltbush. The average annual production of air-dry <br /> vegetation is about 1,200 pounds per acre. If the condition of the range deteriorates, <br /> blue grama, inland saltgrass, fourwing saltbush, and black greasewood increase. Range <br /> seeding is suitable if the range is in poor condition. Important management concerns in <br /> areas of irrigated hay and pasture are preventing a build-up of salts in the root zone of <br /> the soil, efficient application of irrigation water, and maintenance of soil fertility and <br /> tilth. Salt tolerant crops are best adapted to this unit. Irrigation water should be <br /> applied in sufficient amount frequently enough to leach salts downward and prevent an <br /> increase in the salinity of root zone soil water during the growing season. Irrigation <br /> water can be applied by furrow, corrugation, border flooding, and sprinklers. For the <br /> efficient application and removal of irrigation water, leveling is needed in sloping areas. <br /> If row crops or small grains are grown, the use of a crop rotation system that includes <br /> grasses and legumes helps to maintain fertility and tilth. Returning crop residue to the <br /> soil or regularly adding other organic matter improves fertility, reduces crusting, and <br /> increases the water intake rate. Nonleguminous crops respond to nitrogen and <br /> phosphorus, and leguminous crops respond to phosphorus. If properly managed, the <br />