SOIL
What is soil?
• The loose covering of
broken rock particles
and decaying organic
matter (humus)
covering bedrock.
Why is soil important?
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Grow food
Wood for building
Plants provide oxygen
Filter pollutants
How is soil created?
• Rock is chemically and
physically weathered.
• Bacteria, fungi, lichens, &
insects live in weathered
rock.
• These organisms die and
add nutrients to weathered
rock.
• As soil builds, larger
organisms can move in
and colonize.
• Takes 100’s of years to
create a few cm of soil.
What is a soil profile?
• Vertical sequence of soil
layers (horizons).
• O Horizon- vegetation/ leaf
litter on top of soil
• A Horizon- dark-colored thin
layer; rich in organic matter;
humus
• B Horizon- thick layer of
subsoil; may be red or
brown; clay based soil
• C Horizon- contains
weathered parent rock; larger
particles of rock; no organic
matter
• R Horizon- unaltered parent
bedrock
O horizon
R horizon
TYPES OF SOIL
• Polar soil
– Form at high elevations
& high altitudes
– No distinct horizonssoil too thin
– Under top few inches
of soil, ground is
permanently frozenPERMAFROST.
• Temperate soils
– Vary depending on
rainfall & type of
vegetation
– Tropical Grasslandsvery thick, rich, humus
– Forests- thinner, less
fertile clay soil
– Prairies- less rain, so
soil not as thick, but
still fertile.
• Desert soils
– Very thin A horizon
– Very little organic
matter
– High in minerals
– Soil is usually light
colored and coarse
textured.
• Tropical soils
– Intensely weathered
due to high
precipitation and temp.
– Very little humus &
very few nutrients
– High concentrations of
iron- when oxidizes
causes characteristic
red color.
SOIL TEXTURES
• Size of particles determines
– Water holding capacity
– How compacted soil is
– Ability to support plant
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Sand- larger particles
Silt- smaller particles
Clay- smallest particles
Loam- equal mix of sand, silt,
and clay
SOIL CONSERVATION
• Soil is easily eroded.
• Methods to prevent
erosion include:
Contour Farming- plowing along slope
instead of up and down it. Furrows
btwn rows of crops collect water.
•Terracing- series of platforms
are built into slopes. Effective
with steep slopes, slows water
flow.
•Shelter Belts- rows of trees
planted along outer edges of
s creating a windbreak to
prevent wind erosion.
Strip-Cropping- Farmers plow so that
plowed strips are separated by planted
strips. Roots of planted strips hold soil
in place.
• Reduce Grazing
Permits
• Put up fencing
– Animals cannot
compact and destroy
plants