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92—Willowman gravelly sandy loam, 3 to 8 percent <br /> slopes. This deep, well drained soil is on terraces and <br /> fans. It formed in cobbly and gravelly alluvium. The <br /> native vegetation is mainly grass. Elevation is 6,500 to <br /> 7,600 feet. The average annual precipitation is 16 to 20 <br /> inches, the average annual air temperature is 48 to 52 <br /> degrees F, and the average frost-free period is 100 to <br /> 130 days. <br /> Typically, the surface layer is brown gravelly sandy <br /> loam about 8 inches thick. The subsoil is very cobbly <br /> sandy clay loam about 7 inches thick. The upper 6 <br /> inches of the substratum is very cobbly sandy loam, the <br /> next 23 inches is very gravelly loamy sand, and the <br /> lower part to a depth of 60 inches or more is very <br /> gravelly sand. The soil is mildly alkaline to a depth of 15 <br /> inches. Below this depth, it is moderately alkaline and <br /> has large accumulations of calcium carbonate. <br /> Included in this unit is about 15 percent nests of <br /> cobbles on the surface. Also included is about 10 <br /> percent Noden loam in swales and small depressional <br /> areas. The Noden soil has few rock fragments. <br /> Permeability of this Willoman soil is moderate. <br /> Available water capacity is low. Effective rooting depth is <br /> 60 inches or more. Runoff is medium,and the hazard of <br /> water erosion is moderate to high. <br /> Most areas of this unit are used as rangeland. A few <br /> areas are used for irrigated hay and pasture. <br /> The potential plant community on this unit is mainly <br /> sideoats grams, little bluestem, and blue grama. Other <br /> grasses that characterize the unit are prairie junegrass <br /> and needleandthread. The average annual production of <br /> air-dry vegetation is about 1,300 pounds per acre. If the <br /> condition of the range deteriorates, sleepygrass, <br /> threeawn, yucca, and pricklypear increase. Range <br /> seeding is suitable if the range is in poor condition. <br /> Seeding using mechanical equipment is feasible in areas <br /> where the surface is not cobbly. <br /> If this unit is used for irrigated hay and pasture, the <br /> main limitation is the cobbles in the subsoil and, in some <br /> areas, at the surface. Seeding should be feasible in most <br /> areas, but the cobbles can make plowing difficult. <br /> Shallow-rooted crops are best adapted because the <br /> substratum is droughty. <br /> Irrigation water can be applied by corrugations, <br /> flooding from contour ditches, and sprinklers. To avoid <br /> overirrigating and leaching of plant nutrients, applications <br /> of irrigation water should be adjusted to the available <br /> water capacity, the water intake rate; and the crop <br /> needs. Because subsurface cobbles can be exposed, <br /> onsite investigation may be needed before leveling. If <br /> properly managed, this unit can produce 3 tons of <br /> irrigated grass hay per acre. <br /> This unit is poorly suited to windbreaks and <br /> environmental plantings. It is limited mainly by the <br /> droughtiness of the substratum. <br /> This unit is well suited to homesite development. The <br /> large amount of rock fragments in the soil makes <br /> excavation difficult. <br /> This map unit is in capability subclass Vie, irrigated <br /> and nonirrigated. It is in Sandy Foothills range site. <br />