Download Ch. 5 - Soils

Ch 5 - Soils
Important effect of weathering for people!
Important area of study for geologists.
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Objectives
What is soil.
Know soil horizons
and characteristics.
Know 2 types of
soils
Causes &
preventions of soil
erosion
What is Soil?
Soil consists of:
1. Regolith - minerals & rock
fragments
2. Humus - organic matter
3. Gases
4. Water
5. Living organisms
How does soil form?
Five factors influencing soil formation:
1. Climate
2. Parent rock
3. Organisms
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Plants
animals
4. Topography
5. Time
What is a soil profile?
A soil profile consists of several soil
horizons.
O horizon
– humus on the ground surface.
A horizon
– Top soil.
– Rich in organic matter. Typically
dark color.
– Also called zone of leaching.
B horizon
– Subsoil.
– Also called zone of accumulation.
– May contain soluble minerals such
as calcite in arid climates (caliche).
C horizon
– Weathered bedrock (rotten rock).
– Bedrock lies below the soil profile.
Soil
Horizons
– Field
Figure 6. 17
Major Soil Types
• Pedalfer
– rich in Al and Fe.
– form in humid climates
• Pedocal
– rich in Ca.
– form in arid climates
– commonly contain
caliche (or hardpan), a
calcium carbonate
deposit which
accumulates in the soil.
Soft & organic rich
US Soil map
Gray-brown & moist
Strongly weathered & clay rich
Soil Orders
Have you ever had your soil analyzed?
This can be done by county extension
office. Gives you information on:
• pH of your soil.
– Is your soil acidic or basic?
• Elements - Plants require
– P, K, Ca, Mg
– B, Mn, Zn
• Nitrates (fertilizer) –
– N, P, K (in that order)
– listed as weight percents
– Ex. 5-10-5 or 10-10-10.
• Organic matter
• Soluble salts
Particle Sizes
Loam
Loam – Combination of Sand, Silt, Clay
Soil's
productivity is
mainly due to
the clays in the
soils
Names for
Loams
Based on % of
sand, silt, & clay
Soil erosion - (weathering & erosion are different).
• Due to water (runoff)
or wind.
– transported by streams
– deposited on floodplain or
at mouth of river.
– trapped behind dams
• reduces beach sand
• accelerate beach erosion.
• Dust Bowl of the
1930's - due to wind
erosion of soil following
extended drought and
over-tilling of the soil.
Slopes Make it Worse
• 1 % slope = 3 tons soil lost per hectare/yr
• 5 % slope = 87 tons lost per hectare/yr
At this rate a 15 cm thickness of topsoil would
disappear in about 20 years,
• 15 % slope = 221 tons lost per hectare/yr
hectare = 10,000 square meters, or 2.471 acres
How can we slow soil erosion?
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Contour plowing
Terraces
Crop rotation
Planting groundcovers
Windbreaks
Reduce overgrazing