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<br />RIO GRANDE COUNTY AREA, COLORADO
<br />organic matter content and it extends (n a greater
<br />depth than in ~+'ell drained soils.
<br />Lt the mountains and in p:u'ts of the foothills, the
<br />mils fmmerl under various kinds of tegehttion. Some
<br />soils formed under a moderate to thick stand of spruce
<br />and fir trees, others unrlcr mid uul toll grasses, and
<br />scone +mder a cover of pinyon and ,juniper trees.
<br />The most impm'tant function of soil micro-organisms
<br />is the hre:+kdou•n of org;mic pl;mt resirluc. In the Ria
<br />Cr:utrle Guutty Are;+, these processes In'oceed rapidly
<br />in ucll dl~lincd soils as Inng as soil temperature is
<br />Gtcm;lble :uul moisture supplies arc adequate. Conse-
<br />quently, well rlraincrl soils :u'e ch:u<lclerizerl by :+ late
<br />organic matter content, highly stable forms of residual
<br />org;ulic cinnpounds. :utri rlish'ibution p;ttterns where
<br />orl,~:utic matter is concentrated in the upper fen' inches
<br />nF the profile, 1'he nu+ximum amount of organic matter
<br />rnincirlcs +eilh the grcatestconcenlration of plant roots.
<br />In .cites where the hater table keeps the soil moist.
<br />microbial ncli+iL}' proceeds unifurmh' throughout n'arttt
<br />srasnns. In these areas ve;;etation is more luxuriant
<br />and gl'eater nnxnmts of plaint resirluc are rehn'ned to
<br />the soil Gansequentl}, there is n greater accumulation
<br />of decompn.eed organic material :uui it is riistributed
<br />to a greater depth. Such soils are ci:u her colored than
<br />the soils on well drained sites.
<br />In some verp poorly rh'ainerl areas n'here the soil is
<br />wet most of the time, microbial activity is mostly
<br />;utaerobic. Under such conrlilions rlecnmpositiun is often
<br />incomplete, and undecumpused m-ganic nuttls accumu-
<br />late on the surface.
<br />Nonirri~'aterl soils ;ire too drg for earths arm acticit}•.
<br />Rorlenls and other small nnimnls influcnre soil Corma-
<br />tinn by burrowing :ntrl mixing soil horizons and bring-
<br />ing parent material to the sw'face.
<br />Man a(fects soil formation in mans n'a~s. On irri-
<br />gated mils he has ch;utged the climate by adding weter.
<br />'['he crops gron'n often produce large amounts of
<br />organic nutlter that is reltn ned to file soil [n addition,
<br />crops :u'e fertilized.
<br />Tupol; nrpfq
<br />Topography nuldilies the effects of climate :Ind vege-
<br />tation, mainh- ht conh'ollin;,1' the mm~unt of runoff ;uui
<br />the rle;:ree of dY'a111Rge. ~Iall1' SOIIS oC the Hio Grande
<br />County Arca formed on near)}' level hipograph}' that
<br />restrictrrl subsurface drainage. 'These soils occw' ou
<br />(loon plains, maink along the major drainagetcacs :cod
<br />on broad alluvial fans in the eastern part of the surce}'
<br />:u'ea.'fopographyaffects rb'ainage, which in turn affects
<br />plant grnteth and microbial activity. Alamosa, Ger-
<br />rnrd, Acasrn, Schrader, Gunbm•rel. ;lad Norte soils
<br />formed unrlcr restricted drainage. Lack of good drain-
<br />age affect, some of the processes of soi( formation. Fm•
<br />es;unple, the alternate oxidation and reduction ili Cas-
<br />tine soils results in sG•nng mollies.
<br />Some near)>• level soils are n•ell drained, and most
<br />sloping soils ;ue well drained or somewhat excessive)}'
<br />drained. Runn(f is considerable and the resulting ef(ec-
<br />tite precipit;Minn is less than the total amount that
<br />falls. Some nearlc level soils receive additional runoff
<br />from higher areas. On some soils where runoff is rapid,
<br />erosion remotes the soil as rapidly as it forms.
<br />81
<br />Time
<br />Time or age refers to the lengt of time the processes
<br />of soil formation have been activ .Soils that have been
<br />in place for a long time normal y have more distinct
<br />genetic horizons.
<br />The older soils in the survey rea normally have a
<br />B horizon of clay accumulation nd a horizon of cal-
<br />cium carbonate accumulation. Of er soils, such as Villa
<br />Grove and Stunner soils, normal) • hm'e an A, B2t, Cca
<br />horizon sequence.
<br />Younger soils, such as Celest soils, are generally
<br />in material that has not been in place very long and
<br />have ooh' an A, C, m' R hm'izon.
<br />Processes of Soil Formation
<br />Interaction of the soil formin factors in the Rio
<br />Grande County Area has resulted in the accumulaation
<br />of organic matter, mainh• in the A horizon; leaching'
<br />of calcium carbonate from the a per horizons; trvts-
<br />location of silicate clay from the A horizon to the B
<br />horizon; accumulation of soluble salts; and oxidation
<br />and reduction of iron minerals.
<br />Accumulation of organic matt r in the upper Part
<br />of the profile has been impm•tant in most sods of the
<br />survey area. Luhon, Stunner, Travelers, and Zinzer
<br />soils have a strong calcium each hate zone. Evidence
<br />of cla}- movement is shon'n in Em argo, Fulcher, Pla-
<br />toro, Gra}'point, coat Stunner soi s. In such soils as
<br />Platoro and Stunner soils, the hori n of clay accumula-
<br />tion is only about 7 foot below t e surface. in other.
<br />soils, such as Fulcher soils, it ex ends to a depth of
<br />about 3 feet. Accumulation of sot Ible salts is typical
<br />in soils that have poor drainage, f r example, Dlishak,
<br />San Luis, and Arena soils.
<br />Oxidation and reduction are proc sses that are active
<br />in soils that have restricted de•aina e. Vastine and Ala-
<br />mosa soils have a high water tab) most of the year.
<br />Reduction of iron is the result of a Inck oC oxygen, and
<br />the soil becomes mottled and gle}'e Lt some soils, the
<br />water table drops riuring part of th year and the soils
<br />undergo a period of oxidation. In p. •t of these soils, the
<br />n'ater table drops only enough to a Ion' the upper part
<br />of the profile to dry out while the over part remains
<br />tt'et.
<br />Classification of Soils
<br />Soil classification enables us to a semble knowledge
<br />about the soils, to see their relation hip to one another
<br />and to the n•hale environment, and t develop {,rinciples
<br />that help us to understand their haviot• and their
<br />response to management. First thr ugh classification.
<br />and then through use of soil maps, tr'e can apply our
<br />knowledge of soils to specific field and other tracts
<br />of land.
<br />The narrow categories of classifica tat, such as those
<br />used in detailed soil surveys, allow t s to organize and
<br />apply knowledge about soils in mane ing farms, fields,
<br />and woodland; in developing rul.ai areas; in engineer-
<br />ing work; and in many other nays Soils are Placed
<br />in broad classes to facilitate study a d crnnparison of
<br />large areas such as cowtG'ies and con 'nests.
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