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WELD COUNTY, COLORADO, sOUTHERN PART
<br />brief description of the soil profile. In each description,
<br />the principal hazards and limitations are indicated, and
<br />the management concerns and practices needed are
<br />discussed.
<br />The map units on the detailed soil maps represent an
<br />area on the landscape made up mostly of the soil or soils
<br />for which the unit is named. Most of the delineations
<br />shown on the detailed soil map are phases of soil series.
<br />Soils that have a profile that is almost alike make up a
<br />soil series. Except for allowable differences in texture of
<br />the surface layer or of the underlying substratum, all the
<br />soils of a series have major horizons that are similar in
<br />composition, thickness, and arrangement in the profile. A
<br />soil series commonly is named for a town or geographic
<br />feature near the place where a soil of that series was
<br />first observed and mapped. Olney and Nunn, for example,
<br />are names of two soil series.
<br />Soils of one series can differ in texture of the surface
<br />layer or in the underlying substratum and in slope, ero-
<br />sion, stoniness, salinity, wetness, or other characteristics
<br />that affect their use. On the basis of such differences, a
<br />soil series is divided into phases. The name of a soil phase
<br />commonly indicates a feature that affects use or manage-
<br />ment. For example, Olney fine sandy loam, I to 3 percent
<br />slopes, is one of several phases within the Olney series.
<br />Some map units are made up of two or more dominant
<br />kinds of soil. Such map units are called soil complexes and
<br />undifferentiated groups.
<br />A soil complex consists of areas of two or more soils
<br />that are so intricately mixed or so small in size that they
<br />cannot be shown separately on the soil map. Each area in-
<br />cludes some of each of the two or more dominant soils,
<br />and the pattern and proportion are somewhat similar in
<br />all areas. Midway-Shingle complex, 5 to 20 percent slopes,
<br />is an example.
<br />An undifferentiated group is made up of two or more
<br />soils that could be mapped individually but are mapped as
<br />one unit because there is little value in separating them.
<br />The pattern and proportion of the soils are not uniform.
<br />An area shown on the map has at least one of the domi-
<br />nant (named) soils or may have all of them. Loup--Boel
<br />loamy sands, 0 to 3 percent slopes, is an undifferentiated
<br />group in this survey area-
<br />Most map units include small, scattered areas of soils
<br />other than those that appear in the name of the map unit.
<br />Some of these soils have properties that differ substan-
<br />tially from those of the dominant soil or soils and thus
<br />could significantly affect use and management of the map
<br />unit- These soils are described in the description of each
<br />map unit. Some of the more unusual or strongly contrast-
<br />ing soils that are included are identified by a special sym-
<br />bol on the soil map.
<br />Most mapped areas include places that have little or no
<br />soil material and support little or no vegetation- Such
<br />places are called miscellaneous areas; they are delineated
<br />on the soil map and given descriptive names. Rock out-
<br />crop is an example. Some of these areas are too small to
<br />be delineated and are identified by a special symbol on
<br />the soil map.
<br />The acreage and proportionate extent of each map unit
<br />are given in table 4, and additional information on proper-
<br />ties, limitations, capabilities, and potentials for many soil
<br />uses is given for each kind of soil in other tables in this
<br />survey- (See "Summary of tables.") Many of the terms
<br />used in describing soils are defined in the Glossary.
<br />Soil descriptions
<br />1--Altvan loam, 0 to 1 percent slopes. This is a deep,
<br />well drained soil on terraces at elevations of 4,500 to 4,900
<br />feet. It formed in old alluvium deposited by the major
<br />rivers- Included in mapping are small areas of soils that
<br />show evidence of poor drainage. Also included are small,
<br />long and narrow areas of sand and gravel deposits.
<br />Typically the surface layer of the A.Itvan soil is grayish
<br />brown loam about 10 inches thick. The subsoil is brown
<br />and light yellowish brown clay loam and sandy clay loam
<br />about 15 inches thick The substratum is calcareous loamy
<br />sand about 6 inches thick over gravelly sand.
<br />Permeability and available water capacity are
<br />moderate. The effective rooting depth is 20 to 40 inches.
<br />Surface runoff is slow, and the erosion hazard is low-
<br />This soil is used almost entirely for irrigated crops. It
<br />is suited to all crops commonly grown in the area, includ-
<br />ing corn, sugar beets, beans, alfalfa, small grain, potatoes,
<br />and onions- An example of a suitable cropping system is 3
<br />to 4 years of alfalfa followed by corn, corn for silage,
<br />sugar beets, small grain, or beans. The high clay content
<br />and the rapidly permeable substratum slightly restrict
<br />some crops.
<br />All methods of irrigation are suitable, but furrow ir-
<br />rigation is the most common (fig. 4). Proper irrigation
<br />water management is essential. Barnyard manure and
<br />commercial fertilizer are needed for top yields.
<br />Windbreaks and environmental plantings of trees and
<br />shrubs commonly grown in the area are generally well
<br />suited to this soil. Cultivation to control competing
<br />vegetation should be continued for as many years as
<br />possible following planting. Trees that are best suited and
<br />have good survival are Rocky Mountain juniper, eastern
<br />redeedar, ponderosa pine, Siberian elm, Russian-olive, and
<br />hackberry. The shrubs best suited are skunkbush sumac,
<br />lilac, Siberian peashrub, and American plum.
<br />This soil can produce habitat elements that are highly
<br />suitable for openland wildlife, including pheasant, cotton-
<br />tail, and mourning dove- Such crops as wheat, corn, and
<br />alfalfa provide suitable habitat for openland wildlife,
<br />especially pheasant. Tree and shrub plantings and
<br />undisturbed nesting cover would enhance openland wil-
<br />dlife populations.
<br />This Altvan soil has fair to good potential for urban
<br />and recreational development. The chief limiting soil fea-
<br />tures for urban development are the shrink-swell poten-
<br />tial of the subsoil as it wets and dries and the rapid
<br />permeability of the sand and gravel substratum- Septic
<br />tank absorption fields function properly, but in places the
<br />substratum does not contain enough fines to properly
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