Introduction to Soils

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Introduction to Soils
Laboratory Exercise 1
By Carlin Conk
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Definition of Soils

• Soil is the collection of natural bodies on
  earths surface containing living matter and
  supporting, or capable of supporting plants. Its
  upper limit is the atmosphere (air) or water, and
  at its lateral margins it grades to deep water or
  barren areas of rock and ice. Its lower limit is
  normally considered to be the lower limit of the
  common rooting zone (root zone) of the native
  perennial plants, a boundary that is shallow in
  the deserts and tundra and deep in the humid
  tropics.

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Soil Profile

• A soil profile is the vertical display of soil
  horizons.

O
A
E
B
epod.usra.edu/archive/images/100_3733.jpg
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Soil Pedon

• Pedon is a 3-D unit that represents the entire
  soil body and is the smallest volume of soil that
  shows all of the characteristic properties of a
  particular soil.
• Typically represents 10-100 ft2 of surface area.
• A group of pedons is calles polypedons.

www.soils.umn.edu
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Soil Series

• A soil series includes soils that have developed
  from similar materials by similar processes
  resulting in similar appearances and properties.
• The characteristic properties of a soil series
  are unique.
• There are more than 20,000 soil series in the
  United States.

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Soil Series Example
http//ilmbwww.gov.bc.ca/risc/pubs/teecolo/soil/so
il-1.htm
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Soil Color

• Soil color can suggest soil properties that may
  influence plants.
• Dark soil near the surface may indicate a high
  organic matter content, which may lead to easier
  cultivation and higher nutrient content.

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Soil Color in Young Old Soils

• A young, unweathered soil may have a soil of
  uniform color.
• In older, weathered soils, yellow and red colors
  may dominate well below the surface of the soil.
• In North Carolina, we typically have bright red
  subsoils, would this indicate young or old soils?
  Weathered or unweathered?

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Soil Forming Factors

• CL - Climate
• OR - Organisms
• P - Parent Material
• T - Time
• T Topography
• CLORPTT (an easier way to remember the soil
  forming factors)

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Climate

• Climate refers to rainfall and temperature.
• The main effects are weathering, the production
  of organic matter , and the decomposition of
  organic matter.

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Climate of North Carolina

• In North Carolina, rainfall is fairly similar
  across the Piedmont and Coastal Plain. However,
  the rainfall is more variable in the mountains of
  North Carolina.

Mountain
Piedmont
Coastal Plain
http//www.ocs.orst.edu/pub/maps/Precipitation/Tot
al/States/NC/nc.gif
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Organisms or Biotic Activity

• Vegetation is the main biotic factor.
• The type of vegetation affects the soil color and
  organic matter content, especially in the A (or
  top) horizon.

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Grasslands vs. Forests

• Trees contribute less organic matter to the soil
  each year when compared to grasslands.
• The top horizons, or A horizons, in forests are
  usually thinner than A horizons in grasslands.

OM content
http//www.soils.umn.edu/academics/classes/soil212
5/doc/s10chap1.htm
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Parent Material

• Parent materials are defined as the materials
  underlying the soil and from which the soil
  developed.
• There are many different parent materials,
  including
• Residual minerals and rocks (bedrock)
• Glacial deposits
• Loess deposits
• Alluvial and marine deposits
• Organic deposits

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Residual Rocks and Minerals

• Residual minerals weather in place to form soils.

Soil
Bedrock
http//www.gly.uga.edu/railsback/FieldImages.html
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Glacial Deposits

• Glacial deposits formed as massive ice sheets,
  moving across North America, approximately one
  million years ago.
• As the glaciers expanded, they "bulldozed" rocks,
  minerals and soil in front of them.
• As the ice sheets melted, the exposed parent
  material began to weather and soil was formed.

http//www.soils.umn.edu/academics/classes/soil212
5/img/1usglac.jpg
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Glacial Soils
Boulders and Rocks
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Loess Deposits

• Loess deposits formed as high speed winds picked
  up predominantly silt-sized particles and carried
  them across open areas.
• As the wind speed slowed the particles fell to
  the ground covering the native soil and parent
  material.

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Loess Deposits Example
http//esp.cr.usgs.gov/info/eolian/11aNew.jpg
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Alluvial Deposits

• Alluvial deposits refer to sediments carried by
  and deposited in fresh water.
• Flooding events carry rocks and minerals, which
  are deposited in bands.

http//cee.engr.ucdavis.edu/faculty/boulanger/geo_
photo_album
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Marine Deposits

• Marine sediments refer to sediments carried by
  fresh water but deposited in salt water.
• Marine sediments can build up over long periods
  of time until eventually they are quite deep.

http//www.mo15.nrcs.usda.gov/features/gallery/bon
neau.jpg
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Organic Deposits

• Organic deposits originate from plants that have
  died or shed their leaves.
• Organic deposits are common to areas such as
  swamps and marshes since the chemical and
  biological process that decompose the organic
  matter are greatly limited by the saturated
  conditions

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Organic Soils of North Carolina
http//www.soil.ncsu.edu/publications/Soilfacts/AG
-439-26/image2.gif
http//soils.usda.gov/technical/classification/ord
ers/images/histosol.jpg
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Time as a Soil Forming Factor

• We may regard time as continuous yet still
  recognize a "time zero" for a given soil.
• Time zero is the point in time at which a
  catastrophic event (flood or earthquake) is
  completed and a new cycle of soil development is
  initiated.
• Time is important in soil formation because it
  determines the degree to which the other soil
  forming factors express themselves.

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Old Soils

• "Old" soils are those that have experienced
  intense weathering of parent material in the
  presence of biotic factors. These soils will have
  well developed profiles containing A, E, and B
  horizons.

http//soils.ag.uidaho.edu/soilorders/spodosols_02
.htm
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Young Soils

• Young soils have weakly developed horizons and
  may often lack E and B horizons.
• This soil profile lacks any horizon development.

http//soils.usda.gov/technical/classification/ord
ers/entisols.html
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Absolute Age

• If the absolute age of a soil is of interest, a
  soil scientist may measure the activity of
  radioactive carbon.
• Knowing the activity of the radioactive carbon
  the scientist can estimate the age of the parent
  material that has been subjected to weathering.

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Topography

• Topography consists of three parts elevation,
  slope, and aspect.
• Slope is the tilt or inclination of the land.
• Elevation is the height above mean sea level.
• Aspect is the direction the slope is facing.

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Soils on a Steep Slope

• As slopes increase, soils become shallower and
  have thinner and fewer horizons.
• This is because the steeper the slope the greater
  the runoff and the greater the erosion.

http//soils.ag.uidaho.edu/soilorders/inceptisols_
05.htm
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Review of Soil Forming Factors

• Climate
• Organisms
• Parent Material
• Time
• Topography

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Describing Soils

• As a soil develops on the landscape, distinct
  layers or bands parallel to the earth's surface
  may form.
• These layers or bands are called soil horizons.
• Soil horizons, are soil layers that differ from
  the overlying and underlying layers in some
  property, such as color, clay content, abundance
  of cracks, etc.
• Color is one property that is commonly used to
  separate different soil horizons.

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Soil Horizon Layer Designation

• In the United States, soil horizons are
  designated by a code of letters and numbers
  developed by soil scientists of the National
  Cooperative Soil Survey.
• Master horizons are major layers designated by
  capital letter such as 0, A, E, B, C and R.

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Master Horizons O Horizon

• 0 Horizon Organic horizons are dominated by
  organic material.
• The 0 horizons contain organic litter from plants
  and animals.
• 0 horizons are usually present on the soil
  surface except in the case of peats and mucks
  where the 0 horizon extends almost to the bottom
  of the soil.

O Horizon
http//aggieturf.tamu.edu/aggieturf2/golf/layering
.html
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Master Horizon A Horizon

• A Horizon Mineral horizons that have formed at
  the soil surface or just below the 0 horizon.
• The A horizon may contain some organic material
  mixed with mineral material.
• Properties of the A horizon may reflect plowing,
  pasturing or similar activities.

http//soils.ag.uidaho.edu/soilorders/spodosols_02
.htm
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Master Horizon E Horizon

• E Horizon Mineral horizon in which the major
  characteristic is loss of clay, iron and aluminum
  oxides by eluviation or leaching.
• An increase in concentration of sand and silt
  size particles of resistant minerals occurs as
  clay is leached to lower depths.
• Color is lighter than the overlying A horizon.

http//soils.ag.uidaho.edu/soilorders/spodosols_02
.htm
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Master Horizon B Horizon

• B Horizon Mineral horizon that includes layers
  in which illuviation or accumulation of materials
  has taken place.
• Clay, iron and aluminum oxides from the overlying
  E horizon have accumulated here.

http//soils.ag.uidaho.edu/soilorders/ultisols_04.
htm
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Master Horizon C R Horizons

• C Horizon Mineral horizon consisting of
  unconsolidated, partially weathered material that
  is neither soil or rock.
• The horizon is below the zone of most biological
  activity. The upper layer of the C horizon may
  become part of the B horizon as weathering
  continues.
• R Layer Underlying consolidated bedrock

http//soils.ag.uidaho.edu/soilorders/spodosols_01
.htm
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Transitional Horizons

• Transitional horizons are layers of soil between
  two master horizons.

http//soils.ag.uidaho.edu/soilorders/ultisols_04.
htm
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Subordinate Distinctions

• Subordinate distinctions are specific features
  within master horizons that are designated by
  lowercase letters.
• There are many subordinate distinctions such as
• p plow layer
• t accumulation of clay
• b buried layer

http//soils.ag.uidaho.edu/soilorders/ultisols_07.
htm
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Questions?