Soils

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Soils
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Soil Profiles

• General soil profile
• Letters represent horizons
• Numbers are layers within those horizons
• Code
• 0 litter
• A area of leaching and organic matter
  accumulation
• B area of accumulation
• C parent material
• R bedrock

See Text, Fig. 2.8
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Soil formation

• Five main groups of soil forming factors
• climate (present as well as past
• vegetation (influenced by climate and soil fauna)
• parent material
• type of relief
• time

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Mor (coniferous) typical profile

• Prominent organic deposit resting on the mineral
  soil
• Sharp distinction between 0 and A horizons
• Fungi are the main decomposers
• Small biomass of soil animals

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Mull (broadleaf) typical profile

• Bacteria are the chief decomposers
• Soil animals more diverse gt humification
• More mixed upper horizons
• Animal activity also affects the soil porosity

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0
Gradual change
Mor soil
Mull soil
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Components of soil

• Sand (gravel consists of elements over 2 mm)

Silt (.05 - .002 mm)
Clay (less than .002 mm)
Humus (organic)
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Litter build up

• Climate effects the amount of litter and humus
  found in an ecosystem.

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Organic Matter in Soil

• Benefits of Organic Matter
• Improves aggregation and structure
• Improves infiltration
• Improves water holding capacity
• Improves rooting environment
• Slow-release nutrients

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Spaces for Gas and Water

• Particle size effects spaces for gases and water.
• Water movement is dependent on the spaces

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• Adhesion and cohesive forces
• This is called capillary water

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Water movement in different soils
Distance from center of furrow
Sandy Loam
Clay Loam
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• Field capacity vs. gravitational water
• Hygroscopic water vs. available water

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Soil Components
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Nutrient exchange

• Negative charges on clay micelles, humus
  particles and to a lesser extent on silt
  particles
• Cations (K,Ca, Mg, etc.) are attracted to
  the negative charges

K
Ca
Ca
Ca
K
K
Ca
Ca
K
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• Differences in sand, silt, clay, humus
• Size and charge of ion vs. tenacity with which it
  is held
• Order of tenacity with which the cations are
  held
• H gt Ca gt Mg gt K gt Na

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