What
Is
Soil?
Soil is the layer of rock and mineral fragments along with organic matter, water and
air that supports the growth of plants.
The four
components of
soil:
Decomposed rock
Humus
Air
Water
What is Dirt?
Dirt is what gets on
your clothes and
into your house
Controls on Soil Formation
• Parent material – Bedrock vs.
Unconsolidated
• Time – longer time, more soil
• Climate – temperature and
precipitation
• More plants and animals =
more organic matter
• Poorly developed soils on
steep slopes
Soil Texture and Structure
Point A:
10% silt
40% clay
50% sand
Clay loam has
no single
particle size
percentage
that
dominates!
Controls of Soil Formation
If the parent material is bedrock, then
we get residual soils
On unconsolidated sediments, we get
transported soils
Soil composition
-Soil forms in layers
-Larger materials are found on the bottom
How quickly is soil formed?
-It may take several hundred years for 1cm to
form
Soil profile
A vertical column
showing the
sequence of layers
of particles in the
soil
Soil Horizons
-A distinct layer or zone within a profile
-There are four major zones (O, A, B, C)
O zone
-Leaf litter, high decomposition
A Zone
-High organic matter
-Generally the darkest in color
-High humus content
B Zone
-Less developed
-Lighter in color
-Zone of accumulation (highly soluble mineral build-up)
-Red or brown in color
-Clay accumulated (Hard pan formation)
C Zone
-Contains weather parent material
Soil Horizons
O zone
-Leaf litter, high decomposition
A Zone
-High organic matter
-Generally the darkest in color
-High humus content
B Zone
-Less developed
-Lighter in color
-Zone of accumulation (highly soluble
mineral build-up)
-Red or brown in color
-Clay accumulated (Hard pan
formation)
C Zone
-Contains weather parent material
Rill and Gully Erosion
Eroded channels ranging in size from rivulets to small gullies caused mainly by runoff
waters rather than raindrop dislocation.
Gully erosion in Tanzania. What is the main factor for it’s cause?
Who cares about soil erosion?