GES 175: Science of Soils

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GES 175 Science of Soils

• Laboratory
• Week 1

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Soil Development
Soil vs Regolith
Soil weathered portion of regolith

• Regolith
• unconsolidated material above bedrock

bedrock
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• Soil Profile

• contains characteristic layers called horizons

A
E
soil
B
development
Bedrock
C
Bedrock
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Material Transolcation/Development
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Soil Profile
Argixerol
Soil Horizons
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Soil Profile
Soil Horizons
A
Bw
E
BE
Btb
Argixerol
C
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Master Horizons
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Master Horizons
O horizons Layers dominated by organic material.
Some are saturated with water for long periods
or were once saturated but are now artificially
drained others have never been saturated.
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Master Horizons
A horizons Mineral horizons that formed at the
surface or below an O horizon, that exhibit
obliteration of all or much of the original rock
structure -an accumulation of humified organic
matter intimately mixed with the mineral
fraction and not dominated by properties
characteristic of E or B horizons -properties
resulting from cultivation, pasturing, or
similar kinds of disturbance.
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Master Horizons
E horizons Mineral horizons in which the main
feature is loss (eluviation) of silicate clay,
organic matter, iron, aluminum, or some
combination of these, leaving a concentration of
sand and silt particles.
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Master Horizons
B horizons Horizons that formed below an A, E,
or O horizon and are dominated by obliteration of
all or much of the original rock structure (1)
(illuvial) concentration of silicate clay, iron,
aluminum, humus, carbonates, gypsum, or
silica (2)coatings of sesquioxides that make the
horizon lower in value, higher in chroma, or
redder in hue than overlying and underlying
horizons (3)alteration that forms granular,
blocky, or prismatic structure
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Master Horizons
C horizons or layers Horizons or layers,
excluding hard bedrock, that are little affected
by pedogenic processes and lack properties of O,
A, E, or B horizons. Most are mineral layers.
R horizons or layers Hard Bedrock
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12 Soil Orders
I AM A SUAVE HOG or I GAVE US OMAHA
Compliments of Prof. M.J. LaForce
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I AM A SUAVE HOG
Inceptisol- Soils with weakly developed
subsurface horizons Alfisol- Soils
with a subsurface zone of silicate clay
accumulation and gt35 base saturation Mollisol-
Grassland soils with high base status Andisol-
Soils formed in volcanic ash Spodosol-Acid soils
with a subsurface accumulation of metal-humus
complexes Ultisol- Subsurface zone of silicate
clay accumulation and lt35 base saturation
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I AM A SUAVE HOG
Aridosol- Soils in Arid environments with
moderate to strong development Vertisol- Clayey
soils with high shrink/swell capacity Entisol-
Soils with little or no morphological
development Histosol- Organic soils Oxisol-
Intensely weathered soils of tropical and
subtropical environments Gelisol- Soils with
permafrost within 2 m of the surface
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Twelve Soil Orders
Entisol (recent) Inceptisol (L.-inceptum,
begging) Mollisol (L.-mollis, soft) Alfisol
(pedalfter) Ultisol (L.-ultimus, last) Oxisol
(Fr.-oxide)
Increasing Soil Depth
Maturation (loss of Si)
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Twelve Soil Orders
Aridisol (L.-aridus, dry) Spodosol (Gr.-spodos,
wood ashes Gelisol (Gr.-gelid, very
cold) Vertisol (L.-verto, turn) Andisol
(L.-aridus, dry) Histosol (Gr.-histos, tissue)
Climate Specific
Material Specific
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Rock
Ideal Weathering Series
Entisol
Inceptisol
Aridisol (dry climate)
Mollisol
Vertisol (clay mineralogy)
Alfisol
Spodosol (cool and wet)
Ultisol
Oxisol
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Entisol -(ent)

• Shallow to bedrock.
• Limited use and management.
• The most common uses are rangeland

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Inceptisol- (ept)

• Steep slopes and cool climate slow soil
  development.
• Inceptisols are widely distributed and occur
  under a wide range of environmental settings.

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Mollisol -(oll)

• Soil formation under native grassland vegetation

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Alfisol (-alf)

• Alfisols are mostly found in temperate humid and
  subhumid regions of the world.
• Developmentally just past Mollisols

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Histosol -(ist)

• Organic matter is highly decomposed and has few
  remaining plant fibers.

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Vertisol -(ert)

• Abundant, active clay particles are dominant

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Aridosol -(id)

• Form in dry climates
• White crust at the soil surface is a mixture of
  various soluble salts (definitely not snow!).

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Gelisol -(el)

• Permafrost persists below 38 cm year-around.
• The lack of significant microbial activity in
  these soils leads to an accumulation of organic
  matter.

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Gelisols are in very cold climates and typically
contain permafrost
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Web Sites of Interest
NRCS http//www.statlab.iastate.edu/soils/photogal
/orders/soiord.htm
Universities http//soils.ag.uidaho.edu/soilorders
/index.htm
http//soils1.cses.vt.edu/MJE/CSES3124/Laboratorie
s.html
Keys to Soil Taxonomy http//www.statlab.iastate.e
du/soils/keytax/