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<br />84
<br />SOIL SURVEY
<br />solvent activity. Forest organic materials, combined
<br />with the highet• pt•ecipitation of the foothills and
<br />mountains and the low-calcium parent material, greatly
<br />intensify leaching pt•ocesses in these areas.
<br />Small differences in vegetation can be seen on well-
<br />dt•ained soil in any given landscape. Where such differ-
<br />ences occur, it may be difficult to determine the effect
<br />of cegetatio~t on soil formation. Such differences i~t
<br />the vegetation are not necessarily the result of differ-
<br />ences in soil chat•actet•istics, but can reflect other en-
<br />vironmental influences.
<br />The activity of man has influenced the formatiot
<br />of Rock}• Ford soils and other irrigated soils. By pro-
<br />viding irrigation water, man has changed the soil
<br />climate, leading to an increase in the numbet• of eat•tlt-
<br />worms, the amount of microbial activity, and the
<br />amount of plant residue. Intensive tillage, fertilizers,
<br />and the silt-laden irrigation water have made Rocky
<br />Ford soils different from nonirrigated soils. The surface
<br />layer of Rocky Ford soils is 10 to 15 inches thick, and it
<br />is darker colored and more fertile than that of non-
<br />irrigated soils.
<br />Relief
<br />Relief refet•s to differences in elevation and inequali-
<br />ties of the land sut•face, considet•ed collectively. Relief
<br />influences soil formation primarily through its effect
<br />on drainage, runoff, and erosion and secondarily
<br />through variations in exposure to the sun and wind and
<br />in air drainage.
<br />The t•elief of the plains pat•t of the Pueblo Area is
<br />gently undulating; some steep escat•pments at•e oit
<br />terrace edges or below outcrops of limestone or sand-
<br />stone. In the dt•y climate of the plains, the influence
<br />of relief ott soil fot•matiott is mostly through 'its effect
<br />on et•osion. In fine-textured soils, such as those of the
<br />Midway, Razor, and Limon series, the devastating ef-
<br />fect of erosion on pt•ofile development can be seen in
<br />many places. Distinct differences in soil charactet•istics
<br />in places are associated with relatively minor differ-
<br />ences in slope and landforms within a given landscape.
<br />Relief influences soil formation by vit-tue of its effect
<br />on t•ttnoff. Whet•e the total amount of rainfall is small,
<br />slight differences in the supply of moisture can ac-
<br />count for relatively gt•eat differences in vegetation
<br />production and in soil morphology. Soils in concave
<br />areas, where runoff tends to concentt•ate, show mote
<br />evidence of horizonation than soils on the sut•t•ounding
<br />landscape. Fot• example, Baca soils, which are in
<br />slightly concave at•eas, have mote hot•izon development
<br />than Mantel soils.
<br />On ricer and creek bottoms, where the relief is
<br />nearly flat, thet•e is a gt•adient that tends to pt•oduce
<br />lateral movement of ground water from the stream to
<br />the sut•face of the soils. Neatly all of the poot•ly dt•ained
<br />to moderately well drained soils are on flood plains.
<br />Soluble salts tend to accumulate in the surface of these
<br />soils.
<br />In the foothills and mountains, relief influences soil
<br />formation through vat•iation in aspect. North-facing
<br />slopes hace a mote moist, cooler climate than south-
<br />facing slopes. Mortenson soils in the Pueblo Area form
<br />only on not•th-facing slopes in the foothills. Wetmore
<br />and Pinata soils are mostly on north_facing slopes.
<br />Slopes are steeper and differences in elevation greater
<br />itt the foothills and mountains tha:~ on the plains, and
<br />there is more potential fot• runoff. However, more and
<br />taller vegetation attd rock fragments tend to offset
<br />relief and reduce runoff.
<br />Time
<br />The time required for soil horizons to differentiate
<br />in patent material may range from sevet•al decades to
<br />tens of thousands ot• even hundreds of thousands of
<br />years, depending ott the natut•e of the patent matet•ial,
<br />the climate, and the relief. In the Pueblo Area the age
<br />of the soil is usually t•elated to the age of the landform.
<br />The most t•ecent ot• youngest landform occurs on flood
<br />plains of streams. The soils that fot•med iit alluvium on
<br />flood plains have an A hot•izon but do not have a Ca
<br />hot•izon or have only a faint one, as in the Glenberg
<br />and Havet•son soils. The Cascajo soils on high stream
<br />tert•aces fot•med i~t oldet• gravelly alluvium. They have
<br />distinct A and Ca horizons. In loamy and fine-textured
<br />patent matet•ial the degree of development of the B
<br />horizon can be related to the age of the landform in
<br />charactet•istics of structure, colot•, attd clay content.
<br />The B horizon of the oldest soils is usually reddet• and
<br />has stronger structure and distinct, angular blocky
<br />structure.
<br />The age of soils can also be related to stages of
<br />development. In the foothills and mountains in the
<br />western part of the survey area, the factors of climate,
<br />parent matet•ial, and living organisms reinforce each
<br />othet• so that soil horizons differentiate mote rapidly
<br />than on the plains. The landform may or may not be
<br />.older than those on the plains, but because of the more
<br />rapid soil-fot•ming.pt•ocesses the soils are in a more
<br />advanced stage of development.
<br />Youthful soils resemble the patent material in which
<br />they form. Dlature soils have distinct horizons that lie
<br />one above the othet• and are parallel to the earth's
<br />surface.
<br />Classification of the Soils
<br />Soils are classified so that we can more easily re-
<br />member their significant chat•acteristics. Classification
<br />enables us to assemble knowledge about the soils, to
<br />see their relationship to one another and to the whole
<br />environment, and to develop pt•inciples that help us to
<br />understand their behavior and their response to manip-
<br />ulation. First through classification, and then through
<br />use of soil maps, we can apply our knowledge of soils
<br />to specific fields and othet• tt•acts of land.
<br />The nat•t•o~v categories of classification, such as those
<br />used in detailed soil surveys, allow us to organize and
<br />apply knowledge about soils in managing farms, fields,
<br />attd woodlands; in developing rural areas; in engi-
<br />neering work; and in many other nays. Soils are
<br />placed in broad classes to facilitate study and compari-
<br />son in large areas, such as countries and continents.
<br />The system of soil classification currently used was
<br />adopted by the National Coopet•ative Soil Survey in
<br />1965. Because this system is under continual study,
<br />readers intet•ested in developments of the current sys-
<br />tem should search the latest literature available (10).
<br />K-2
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