THE SOIL PROFILE
The 6 Soil Roles
A Soil’s role includes:
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Serving as a foundation
Emitting and absorbing gases
Providing habitat
Interacting with water
Recycling nutrients
Supporting human settlements
The 5 Factors of Formation
Soil is formed by…
• Parent Material: the original “Mom & Pop” soil transported from
elsewhere, usually by wind or water, at different speeds
• Climate: the amount, intensity, timing, and kind of precipitation
that breaks down parts of ecosystem (i.e. rocks, trees) into soil
• Topography: Slope and Aspect affect the angle of the land and
position toward/away from the sun that soil will be exposed to
• Biological: Plants, animals, microscopic organisms, and humans
interact with soil in different ways
• Time: the amount of time it takes for the four factors (above) to
interact with each other
What is a Soil Profile?
• A Soil Profile is a vertical cross-section of layers of soil found
in a given area. Below are two examples of soil profiles.
What is a Soil Horizon?
• Soil horizons are the layers in a soil profile used to classify soil
types.
• Horizons based on color, texture, roots, structure, rock
fragments, and any unique characteristic worth noting.
• Master Soil Horizons are depicted by a capital letter in the
order (from top down): O, A, E, B, C, and R
O-Horizon
The “Organic Matter” Horizon
• Surface-layer, at depths of 0-2 feet
• Dark in color, soft in texture
• Humus - rich organic material of
plant and animal origin in a stage of
decomposition
• Leaf litter – leaves, needles, twigs,
moss, lichens that are not
decomposing
• Several O-layers can occur in some
soils, consisting only of O-horizons
A-Horizon
“Topsoil” or “Biomantle”
Horizon
• Topmost layer of mineral soil, at
depths of 2-10 feet
• Some humus present, darker in color
than layers below
• Biomantle - most biological productive
layer; earthworms, fungi, and bacteria
live this layer
• Smallest and finest soil particles
E-Horizon
The “Leaching Layer” Horizon
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Small layer between A & B horizons
At depths of 10-15 feet
Light in color, mainly sand & silt
Poor mineral and clay content due to
leaching – the loss of water-retaining
plant nutrients to the water table
• Soil particles larger than in A horizon
but smaller than in B horizon
B-Horizon
The “Subsoil” Horizon
• At depths of 10-30 feet
• Rich in clay and minerals like Fe &
Al
• Some organic material may reach
here through leaching
• Plant roots can extend into this
layer
• Red/brown in color due to oxides
of Fe & clay
C-Horizon
The “Regolith” Horizon
• At depths of 30-48 feet
• Made up of large rocks or lumps of
partially broken bedrock
• Least affected by weathering and
have changed the least since their
origin
• Devoid of organic matter due to it
being so far down in the soil profile
R-Horizon
The “Bedrock” Horizon
• At depths of 48+ feet
• Deepest soil horizon in the soil
profile
• No rocks or boulders, only a
continuous mass of bedrock
• Colors are those of the original
rock of the area
How to Make a Soil Profile
Ingredients List
• 3-4 copies of Master Soil Horizons Worksheet
Directions
1.
In large glass bowl, whisk 3.5 cups milk with 2
pkgs. vanilla Instant Jell-o pudding mix until
smooth. Let stand 5 minutes.
2.
While waiting, refer to your version of “The
Soil Profile” powerpoint to review order that
horizons should be. You have A, E, B, R, O, C,
and vegetation as horizons. It’s up to you to
order it!
3.
After 5 minutes, use spatula to scoop pudding
in middle of bowl, allowing for the “dry
ingredients” (the bags of various crushed up
cookies) to encircle the pudding along the
sides of the glass bowl. This creates a vertical
cross-section of soil layers visible to you.
4.
Use sticky notes to label each horizon on
outside of bowl.
5.
Fill out Master Soil Horizons Worksheet using
observations of Soil Profile Dessert.
6.
Turn in worksheet to teacher. Only until you
and your team members turn in their
worksheet can you enjoy the delicious snack.
You’re finished!
• 30 sticky notes per group (7 per person)
• 3-4 pairs of gloves
• 1 large glass bowl
• 1 one-cup measuring cup
• 1 whisk
• 1 spatula
• 3.5 cups skim milk
• 2 packages vanilla Instant Jell-o pudding mix
• 1 tiny Ziploc bag Coconut w/green food coloring + raisins
• 1 small Ziploc bag crushed chocolate graham crackers &
frosting
• 1 medium Ziploc bag Chocolate chip & Vanilla wafers &
gummy worms
• 1 small Ziploc bag crushed Vanilla wafers only
• 1 medium Ziploc bag crushed graham crackers
• 1 large Ziploc bag crushed Oreo cookies
• 1 large Ziploc bag crushed chocolate chips