Download STATION 4) Soil Horizons in a Soil Profile What is a soil profile? It is

Staple to back of your booklet when done!
STATION 4) Soil Horizons in a Soil Profile
What is a soil profile?
It is a vertical cross-section of a soil in place.
» Turn to p. A124 in your textbook. Read this plus
the handout provided to find the answers for the
blanks below.
» Label the layers with the correct letter.
- Soil profiles are divided into a series of
horizontal layers that differ from each other.
These layers are called horizons.
- The layers at the top and the bottom are not
strictly part of soil horizons, but are included since
they are so important! (They are not in the
textbook version but ARE in Mr. Nickens’ PPT video
on soil horizons and in the handout.)
- The top “horizon, the O “horizon”, is usually a thin layer of __________ material—
dead ___________, plants or grasses that have collected and have started to
_________ down.
- The upper soil horizon, the A horizon, is also known as “______________”. It has
the most organic matter, or ________, is often dark-colored, and is rich in nutrients.
Animals and plants that live in soil are found here—they help ___________ and aerate
this horizon.
- The B horizon, also called “_____________”, lies beneath the A horizon. It has little
humus and is often red or brown in color (if well-drained) or gray (if poorly drained). It
can have sandy or silty materials but often is where clay and minerals have washed down
to be. A young soil may have little to no B horizon. It is called “__________”. A soil
with 3 or more layers above the bedrock is called “mature”.
- The C horizon, lies below the B horizon. It has recognizable pieces of rock that are in
the process of being weathered and is generally the thickest layer. A typical color is
light ______________________.
- The bottom layer, the R “horizon”, is the consolidated, or solid, ____________ from
which the soil above it was formed.
Reading to help complete Station 4:
CLASS COPY REFERENCE – Do not take!
Taken from: http://education.usgs.gov/lessons/soil.pdf
The grouping of identifiable layers of different
components and characteristics that make up a soil in
a given area is referred to as a soil profile.
Each individual soil layer is referred to as a horizon,
termed 0, A, B, and C.
• The 0 Horizon is usually a thin top layer of
organic material—dead leaves, plants or grasses
that have collected and begun to break down.
• The A horizon, or "topsoil," is dark-colored, rich
in nutrients, and lies directly below the 0 horizon.
Most soil-dwelling animals and plants are found in this layer, and their
presence helps loosen and
aerate this horizon.
• The B horizon, or "subsoil," lies beneath the A horizon. Although this
horizon can contain sandy or silty layers, it is mostly characterized by
clay-sized particles.
- This layer is usually much more compact than the A horizon. If a B
horizon is thin or missing because weathering processes have not
been at work long enough, a soil is said to be immature. If a soil
profile contains at least three layers above the unweathered bedrock,
it is said to be mature.
• The C horizon exists beneath the B horizon. The C horizon has no
properties typical of the overlying horizons, but it has been affected by
weathering processes such as oxidation. It is composed of
unconsolidated material that may or may not be like the material from
which the soil presumably formed. Directly underneath this horizon,
and therefore beneath the entire soil profile, lies consolidated
bedrock.
• The R “horizon” is the consolidated (solid) bedrock from which the
soil was formed.