Ch 5 Soils

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Ch 5 - Soils

• Important effect of weathering for people!
• Important area of study for geologists.

• Objectives
• What is soil.
• Know soil horizons and characteristics.
• Know 2 types of soils
• Causes preventions of soil erosion

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What is Soil?

• Soil consists of
• Regolith - minerals rock fragments
• Humus - organic matter
• Gases
• Water
• Living organisms

3
How does soil form?

• Five factors influencing soil formation
• Climate
• Parent rock
• Organisms
• Plants
• animals
• Topography
• Time

4
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.

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Soil Horizons Field
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Figure 6. 17
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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.

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US Soil map
Gray-brown moist
Soft organic rich
Strongly weathered clay rich
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Soil Orders
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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

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Particle Sizes
Loam
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Loam Combination of Sand, Silt, Clay
Soil's productivity is mainly due to the clays in
the soils
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Names for Loams
Based on of sand, silt, clay
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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.

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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

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How can we slow soil erosion?

• Contour plowing
• Terraces
• Crop rotation
• Planting groundcovers
• Windbreaks
• Reduce overgrazing