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Soil Origin and Development
Original by Nancy Williams
Modified by Georgia Agricultural Education
Curriculum Office
July, 2002
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.
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
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
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.
Rocks and Minerals
Sedimentary rockIs 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 rocklike basalt,formed from molten rock as in
volcano. Most of the earth’s crust is igneous
rock overlain by sedimentary rock
Rocks and Minerals
Metamorphic rock- has been altered by heat,
pressure or chemical action. Examples are
limestone becomes marble and sandstone
becomes quartzite.
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.
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.
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
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.
The Soil Profile
Soil does change over time today Scientist have
classified them into four areas
They are:
–
–
–
–
Addition
Losses
Translocations
Transformations
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
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.
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.
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.
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.
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.
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.
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
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.
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.
Horizons
The E Horizon– This is the zone of the greatest leaching of clay,
chemicals and organic matter.
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
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
Horizons
The R Horizon– Is the underlying bedrock such as the limestone,
sandstone, and or granite.