What Is Soil?
The four components of
soil:
Decomposed rock
Humus
Air
Water
Soil is the layer of rock and mineral fragments along with organic matter, water and air that supports the growth of plants.
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 StructurePoint A:
10% silt
40% clay
50% sand
Clay loam has no single
particle size percentage that
dominates!
Controls of Soil FormationIf the parent material is bedrock, then
we get residual soilsOn 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 HorizonsO 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?
