Soils 205- General Soils

Lecture 2 Handout - Soil as a Natural Body

I.  Soil at different scales

 

                       

  The soil vs. a soil-
If "the soil" is thought of like a forest, "a soil" would be an individual tree in that forest

 

 

 

 

 

 

II.  Some Terminology

Soil, Regolith, and Bedrock:

Regolith- unconsolidated layer above hard, unweathered, bedrock

Solum- upper portion of the regolith that has been altered through biochemical and physical processes.  The material between the solum and bedrock is referred to as the C horizon.  It is slowly changing into solum.

Pedon- a 3-D sampling that displays the full range of properties that are characteristic of a soil (1-10 m2).

Soil Profile- one vertical face of a pedon. 

Soil Horizons- horizontal layers, differentiated by color or texture, described within a profile

A, B, and C horizons                a profile is one face of a  pedon (3-D)
in a soil profile

 

III. Soil horizons

      a.  Master horizons- indicate a dominant process; there are six different master horizons that we describe in the field

           i.  O horizon- organic horizon (> 20% organic material by weight); found in wetlands and forest litter layers 

        ii. A horizon-  

 

 

iii.  E horizon-

 

 

            iv.  B horizons-

 

 

            v.  C horizons-

 

            vi.  R horizons- hard, unweathered bedrock

 

IV.  The order of soil horizons

 

V.  Special cases

    a.  Transition horizons-

    b.  Lithologic discontinuity-

 

VI.  Subordinate distinctions-

    a.  B horizons always have a subordinate distinction:

            Bt - clay has accumulated

            Bk- CaCO3 has accumulated

            Bs - Fe and/or Al oxides have accumulated (illuviation)

            Bo - Fe and/or Al oxides have accumulated (intense weathering)

            Bw - distinct color or structure; sig. alteration of the parent material

            Bh- illuvial organic matter

            Bg - horizon has gray colors associated with high water tables

            Bx - fragipan (dense, brittle)

            Bkm - horizon is cemented by calcium carbonate

            Bkqm - horizon is cemented by calcium carbonate and silica

    b.  O horizons always have a subordinate distinction

        Oi - slightly decomposed organic matter

        Oe - moderately decomposed organic matter

        Oa - highly decomposed (muck)

    c.  other master horizons may or may not have subordinate distinctions:

        Ap - plowed horizon

        Ab - buried horizon

        Cr - soft or weathered bedrock