Soil Profiles and Horizons

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Soil Profiles and Horizons
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AcknowledgementThis work was supported in
part by the National Decentralized Water
Resources Capacity Development Project with
funding provided by the U.S. Environmental
Protection Agency through a Cooperative Agreement
(EPA No. CR827881-01-0) with Washington
University in St. Louis.  The results have not
been reviewed by EPA or Washington University in
St. Louis. The views expressed in this
presentation are solely those of NCSU, and
University of Arkansas and EPA and Washington
University in St. Louis do not endorse any
products or commercial services mentioned in the
presentation.
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Citation

• -Lindbo, D.L., M. H. Stolt, R. Miles, and D. L.
  Mokma. 2005. 3. Field Description of Soils Soil
  Horizons Power Point Presentation. in (D.L.
  Lindbo and N. E. Deal eds.) Model Decentralized
  Wastewater Practitioner Curriculum. National
  Decentralized Water Resources Capacity
  Development Project. North Carolina State
  University, Raleigh, NC.

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Soil Profile Language

• There is a standard nomenclature or language
  used to describe soils
• The ability to understand the nomenclature used
  by soil scientists aids in communication between
  the installer, designer, and regulator
• Often the nomenclature will identify features in
  the soil that have a direct bearing on soil
  properties related to wastewater treatment and
  dispersal

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Soil Profile Descriptions

• Soil Profile - A vertical section of the soil
  extending through all its horizons and into the
  parent material.
• Soil Horizon - A layer of soil, approximately
  parallel to the surface, having distinct
  characteristics produced by soil forming
  processes.
• Soil Layer - A layer in the soil deposited by a
  geologic force (wind, water, glaciers, oceans,
  etc.) and not relating to soil forming process.

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Soil Horizon Designations

• Soil horizons designated by a combination of
  CAPITAL LETTERS-lower case letters-ARABIC
  NUMERALS
• Master Horizons and Layer Major breaks in the
  soil O, A, E, B, C, and R.
• Subordinate Distinctions Lower case letters
  used as suffixes to designate specific master
  horizons. i.e. Ap, Bw, Cg
• Vertical Subdivisions A horizon designated by a
  single combination of letters which needs to be
  subdivided. i.e. Bw1, Bw2, Cg1, Cg2.

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Organic (O) Horizons

• O horizons or layers Layers dominated by
  organic material.
• Field Criteria
• 18 organic matter
• Dark color (never used by itself)
• Low strength, light dry weight, high fiber
  content
• Typically a surface horizon-if buried may
  indicate disturbance
• Subordinate Distinctions of O Horizon
• Oa-Highly decomposed organic material (Muck)
• Oe-Moderately decomposed organic material (Mucky
  Peat)
• Oi-Slightly decomposed organic material (Peat)

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O Horizons Considerations

• Limitations to on-site wastewater
  treatment/disposal
• Fire hazard
• Low strength
• Low permeability
• Wet
• Limitation only when the O horizon is
  sufficiently thick
• Regardless of thickness the above limitations
  still must be considered

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A Horizons

• Referred to as topsoil and typically ranging from
  1-12 inches (2-30 cm) thick (may be more in
  certain circumstances). Mineral horizon formed
  at the surface or below an O horizon.
  Characterized by an accumulation of humified
  organic matter intimately mixed with the mineral
  fraction.
• Field Criteria
• Mineral soil material
• Mix of well decomposed organic matter and mineral
  material
• Surface mineral horizon
• Typically dark in color-darker than underlying
  horizons
• Typical Subordinate Distinctions of A Horizon
• Ap-Plowing or other disturbance

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A Horizon
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Ap Horizon
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A Horizon gradual boundary
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Clod from plow
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A Horizon Considerations

• Generally, suitable structure (granular)
• Offer high degree of treatment potential due to
  higher OM content.
• Evaluate and Ap for potential plow pan
• Evaluate for redoximorphic feature
• Redox concentrations-pore linings
• Redox depletions-low chroma areas

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E Horizons

• Mineral horizon in the upper part of the soil
  typically underlying an O or A horizon. Light
  colored, leached horizons ranging from not being
  present to several centimeters thick
• Field Criteria
• Zone of eluviation - removal of clays, Fe, Al,
  and humus
• Lighter in color than over or underlying horizon
• Near surface, below O or A horizons and above a B
  horizon

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E Horizon (cont.)

• Formed by weak organic acids that strip coatings
  (clay, OM, Fe, etc.) from sand grains. Light
  color due to the natural color of the mineral
  grains.
• Subordinate Distinctions of E Horizons
• Eg-Strong gleying, indicates prolonged periods of
  saturation
• Ex-Fragipan dense, restrictive horizon

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E Horizon
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E Horizon
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E Horizon
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E Horizon
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E Horizon Considerations

• Structure variable
• Must determine if the colors are due to leaching
  or redox conditions or both
• May restrict water movement
• Thickness-if restrictive can it be removed?

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B Horizons

• Referred to as subsoil. They are the zone of
  accumulation with in the soil. In well drained
  soils it has the brightest colors. May extend
  over a meter below the surface.

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B horizon (cont.)

• Field Criteria
• Subsurface horizon formed below an O, A, E
  horizon and above the C horizon
• Formed as a result of soil forming processes
• Weakest expression is color development
• Illuvial concentration-zone of accumulation
• Single grained or weak structure not massive
• Subordinate Distinctions of B Horizons
• Bw-Development of color or structure
• Bt-Accumulation of clay
• Bg-Strong gleying, indicates prolonged periods of
  saturation
• Bh-Illuvial accumulation of humus
• Bs-Illuvial accumulation of sesquioxides
• Bm-Cementation or induration
• Bx-Fragipan dense, restrictive horizon
• Bv-Presence of plinthite
• Bss-slickensides

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Bw Horizon Considerations

• Weakly structured but not massive
• May contain redoximorphic features

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Bw Horizon
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Bw Horizon
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Bw Horizon
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Bt Horizon Considerations

• Higher clay content than overlying horizon
• Weakly to strongly structured
• May appear massive in auger borings
• Can restrict water movement even if no
  redoximorphic features are present
• May contain redoximorphic features particularly
  around roots and ped faces

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Bt Horizon
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Clay Skin
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Bg Horizon Considerations

• Formed under saturated and reduced conditions
• Indicative of water table for long duration (gt 21
  days)
• May contain some redox concentrations
• Must have value gt4 and chroma lt2

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Bg Horizon
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Bg Horizon
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Bh Horizon Considerations

• Hummus accumulation-feel greasy
• Primarily found in sandy textured soils
• May indicate high water table (Aquod) or not
  (Orthod)
• May or may not be restrictive to water movement
• Multiple Bh horizons may occur

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Bh Horizon
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Bh Horizon
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Bs Horizon Considerations

• Sesquioxde (Fe and Al-oxides) accumulation often
  associated with Bh horizons
• Primarily found in sandy textured soils
• May contain redoximorphic features
• May indicate high water table (Aquod) or not
  (Orthod)
• May or may not be restrictive to water movement
• Multiple Bs horizons may occur

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Bs Horizon
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Bs Horizon
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Bs Horizon
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Bss Horizon Considerations

• Formed by shrinking and swelling of clays.
• Low permeability
• Can disturb foundations etc.

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Bss Horizon
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Bss Horizon
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Bm Horizon Considerations

• Cemented horizons
• Restrictive to water movement
• Variable thickness

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Bm Horizons
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Bm Horizon
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Bx Horizon Considerations

• Apparently cemented horizon but will slake in
  water
• Dense and brittle
• Appear massive but may have a secondary prismatic
  structure
• Restrictive to water movement often causing a
  perched water table
• May contain redoximorphic features

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Bx Horizon
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Seam
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30 cm (12 inches)
Plan View
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Bv Horizon Considerations

• Contains plintihite
• May be restrictive to water movement

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Plinthite
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Bv Horizon
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C Horizon

• Referred to as substratum. These horizons and
  layers are little affected by soil forming
  processes (unweathered geologic material).
• Field Criteria
• Little affected by soil-forming processes
• Geologic layering
• Lack of color development, color of unweathered
  geologic material
• Subordinate Distinctions of C Horizons
• Cd-Dense unconsolidated sediment
• Cg-Strong gleying, indicates prolonged periods of
  saturation
• Cr-Weathered or soft bedrock
• Ck-Presence of carbonates

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C Horizon Considerations

• Shows little evidence of alteration yet can be
  easily dug with a spade.
• Water movement through it will be primarily
  controlled by its texture
• May or may not exhibit redoximorphic features

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C horizon
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C horizon
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C or Cr Horizon Considerations for Residual Soils

• Saprolite, can be dug with a spade
• May contain redoximorphic features
• May or may not be restrictive to water movement

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C horizon
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C horizon
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Cr horizon
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Cd Horizon Considerations

• Dense, often massive
• May contain redoximorphic features
• Restrictive to water movement

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Cg Horizon Considerations

• Formed under saturated and reduced conditions
• Indicative of water table for long duration (gt 21
  days)
• May contain some redox concentrations

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Cg Horizon
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Cg Horizon
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Ck Horizon Considerations

• Contains free carbonates

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R Horizons

• Bedrock that can not be dug with a spade

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Soil Surface
Lithologic Discontinuity or R horizon
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Transitional and Mixed Horizons

• Transitional horizons
• Combine master horizon designations
• i.e. AE is an horizon that is more A than E but
  has characteristics of both, an EA is more E than
  A
• Mixed horizons
• Combine master horizons with a slash (/)
• i.e. A/E is an horizon with E material mixed into
  dominantly A material

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A vs E horizon

• A horizons have a high OM content
• E horizons have low OM content
• E horizons often feel sandier (coarser) than the
  A horizon
• E horizons have a higher value and chroma

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E vs B horizon

• E horizons are sandier (coarser) than B horizons
• E horizons are higher in value and chroma
• B horizons have more clay
• B horizons have more Fe

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Examples
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Fripp Series
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Ousley Series
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Stockade Series
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Goldsboro Series
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Rains Series
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Chewacla Series
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Dothan Series
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Wagram Series
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Appling Series
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Cecil Series
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Green Level Series
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Hiwassee Series
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Tate Series
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Buladean Series
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Biltmore Series
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Hayesville Series
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Burton Series
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Wayah Series