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Soil Origin and Development
Original by Nancy Williams
Modified by Georgia Agricultural Education
Curriculum Office
July, 2002
August 2008
Soil Body
• Terms to know:
– Pedon is a section of soil extending from the
surface to the depth of the root penetration of
the deepest rooted plants.
– Polypedon a collection of pedons that are
much the same.
– Weathering it is where weather, plants are
the major agents responsible for forming soil
from rock.
August 2008
Soil Body
• Physical Weathering– refers to the effects of such climatic factors
as Temperature, water, and wind. One of the
most important is frost wedging.
– Chemical Weathering- changes the chemical
makeup of rock and breaks it down.
– Hydrolysis- water reacts with minerals to
produce new and softer compounds
August 2008
Rocks and Minerals
• Igneous Rock:
– it is the basic material of the earth’s crust. It
is created by the cooling and solidification of
molten materials from deep in the earth.
– Sedimentary Rock
• Forms when loose materials like mud or
sand are deposited by water, wind, and
other agents
August 2008
Rocks and Minerals
• Metamorphic Rock:
– This is where igneous and sedimentary rocks
are subjected to great heat and pressure so
they change to metamorphic rock.
August 2008
Rocks and Minerals
• Sedimentary rock• Is like limestone or sandstone,formed by
deposition of materials in water or by wind.
Note: fresh mud and sand that will someday
be sedimentary rock.
• Igneous rock• like basalt,formed from molten rock as in
volcano. Most of the earth’s crust is
igneous rock overlain by sedimentary rock
August 2008
Rocks and Minerals
• Metamorphic rock- has been altered by
heat, pressure or chemical action.
Examples are limestone becomes marble
and sandstone becomes quartzite.
August 2008
Rocks and Minerals
• What is Residual Soil– this is soil formed right from bedrock. They
are actually less common than soils of parent
material carried from elsewhere by wind,
water, ice and or gravity.
– They form very slowly as the rock must be
weathered first.
August 2008
Rocks and Minerals
• Glacial Ice– Carried parent materials all over the northern
part of the North America during the four
separate periods of glaciations
– What is glacial drift?
• It is the melting and the shrunk between the
glacial periods and transported materials remained
in deposits. This is how we got the most beautiful
landscapes in the United States.
August 2008
Rocks and Minerals
• What is Glacial Till– It is the melting process where some debris
simply dropped in place to form deposits.
Eolian is where the wind will carry and leave
soil somewhere else.
Alluvial Soils- are soils whose parent
materials were carried and deposited in
moving fresh water to form sediments
August 2008
Rocks and Minerals
• Colluvium– this is where the soil will slide down or roll
down a slope. This is scattered in hilly and
mountainous areas
– Some examples are: Avalanches, mudslides,
and landslides.
August 2008
The Soil Profile
• Soil does change over time today Scientist
have classified them into four areas
• They are:
– Addition
– Losses
– Translocations
– Transformations
August 2008
The Soil Profile
• What is Additions?
– It is materials such as fallen leaves windblown
dust or chemicals from air pollution may be
added to the soil
August 2008
The Soil Profile
• What is Losses?
– It is materials that may be lost from the soil
as a result of deep leaching or erosion from
the surface.
August 2008
The Soil Profile
• What is Translocation?
– It is materials that may be moved within the
soil as with leaching deeper into the soil or
being carried upward with evaporating water.
August 2008
The Soil Profile
• What is Transformation?
– It is the materials that may be altered in the
soil, for example organic matter decay
weathering of the minerals to smaller particles
or chemical reactions.
August 2008
The Soil Profile
• Each of these processes will occur at
different depths of the soil.
• For example:
– Organic Matter will be at the top or the near
the surface of the soil.
August 2008
The Soil Profile
• What is a horizon?
– They are the layers of the different types of
soil and the different depths that the layers
will be located at.
August 2008
The Soil Profile
• What is a soil profile?
– It is the vertical section through the soil and
extending into the unwreathered parent
materials and exposing all the horizons.
August 2008
Master Horizons
• What is the Master Horizons?
– The are A, B and C horizons are known as the
master horizons. They are a part of a system
for naming soil horizons in which each layer is
identified by a code O, A, E, B, C and R
August 2008
Horizons
• The O Horizon– Is the organic layer made of wholly or partially
decayed plant material and animal debris .
You can normally find this layer in a forest
with fallen leaves, branches and other debris.
August 2008
Horizons
• The A Horizon– It is usually called the topsoil by most farmers.
This is where the organic matter accumulates
over time. This layer is very prone to leaching
and losing iron and other minerals. The A
horizon provides the best environment for the
growth of plant roots, microorganisms and
other life.
August 2008
Horizons
• The E Horizon– This is the zone of the greatest leaching of
clay, chemicals and organic matter.
August 2008
Horizons
• The B Horizon– This is also called the subsoil is often called
the zone of accumulation where chemicals
leached out of the A horizon
August 2008
Horizons
• The C Horizon– lacks the properties of the A and B horizon. It
is the soil layer that is less touched by soil
forming processes and is usually the parent
material soil
August 2008
Horizons
• The R Horizon– Is the underlying bedrock such as the
limestone, sandstone, and or granite.
August 2008