Lecture 3a Naming Soil Horizons  Soil horizons (layers in the soil) are named so differences between soils can be identified.  Naming soil horizons takes practice

 When soil scientists are describing a soil they will discuss a lot about what they are seeing and how it should be named.  And what they are not seeing and what it should not be called ?

Organic Horizons O - horizon - organic material (no mineral materials) 1) forest litter 2) organic soil or peat soils, or muck  Oi - undecomposed (fibris)  Oe - moderate decomp. (hemis)  Oa - decomposed (sapric)

Organic Soil Profile This trenching machine is digging through the Oe horizon of an organic soil. Trenches needed to remove water so the peat will dry before harvest.

Organic Soil Horizons in a forest litter Oi Oe

Processes of Mineral Soil Horizon Formation u A. Additions - H2O, organic matter,air, soil particles, salt u B. Losses - H2O, organic matter, CO2, nutrients by plant removal u C. Transformations - Changes to soil structure, development of clay minerals, weathering of minerals to elements, chemical Rx u D.Translocations - movement from one horizon to another of O.M. Clay, Water, Iron, & Nutrients in colloidal size, (very small particles) clay films on peds are evidence of this translocation = clay (film) coating

Mineral Soil Horizons  A horizon - surface horizons that accumulate O.M.  Ap = plowed soil Ap EB Bt BC C

E Horizons  E - (formerly A2) - Translocation out - Zone of Eluviations - Leaching out  lighter in color than horizons above or below A E E/ B Bt BC C

B Horizons- two kinds :  a) Translocation in - below an A, E, or O with an accumulation of clay, iron, humus (O.M. decomposed.) or carbonates (CaCO3) zones of illuviation  b) or alteration of the original parent material, development of color or structure - Bw Bt

C Horizons  C - little affected by pedogenic processes and lack properties of O-A-B- E- or is the Parent Material C horizon Solum = A + B

Rock Horizons  R = hard rock  Cr = Soft Rock

Subscripts - all B horizons have a subscript, most transition horizons do not.  * a - sapric - organic soils - well decomposed  * b - buried soil horizon  d - dense - geogenic soil material (compacted by glacier)  * e - hemic - mod. decomp. - organic soil  f - frozen soil - permanently frozen, permafrost  * g - gleyed soil - gray color due to low O2 - reduction of Fe  * h - accumulation of humus - O.M. other than in the A or O horizons  * i - fibric - organic - non-decomposed  * k - accumulation of calcium carbonate (CaCO3)  * m - cementation - hard - indurated

u n - sodium accumulation u * p - plowing - only used with A u q - silica accumulation - very weathered or old soil u * r - soft rock - used with C or Cr u * s - sesquioxides (1.502) (Fe2O3) accumulation of Fe and Al - red color u *ss – slickensides present –shiny surface on ped face caused from soil rubbing against soil u * t - clay accumulation - clay films u * w - color or structure development (Bw) u x - Fragipan - hard, dense layer that developed with time u y - gypsum accumulation (CaSO4) u z - salts more soluble than gypsum (KCL - NaCl - NaSO4) Subscripts cont.

Transition Horizons  AB - Like A - some of B  BA - Like B - some of A  AE AC BC  E/B - Both E and B particles are present -  “B & E” used for soils with Lamellae - thin bands of accumulating clay and iron in sandy soils