Weathering and Soils

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Weathering and Soils
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Regolith-

• The layer of weathered rock fragments beneath the
  soil and above the bedrock (solid rock).

? Soil ? Regolith ? Bedrock
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Soil Components

• Regolith is the basis for soil
• Soil minerals, water, gases, organic mtl.

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• humus- dark, organic material made of decayed
  animal and plant remains
• Found just beneath the vegetation
• Important part of soil- provides nutrients!

? Humus
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3 types of rock materials make up soil-
classified by the size of the particles.

• Sand (0.05 2 mm in dia.)
• Silt (0.002 to 0.05 mm)
• Clay (lt0.002 mm in dia.)
• The amounts of each of these components depends
  on the parent rock!

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Soil Facts

• Lichens-die add organic nutrients to soil
• Slowly renewable resource- 1cm15 or more years
• Filters water-infiltration?leaching (diluting
  nutrient rich layers) into aquifers/surface
  runoff
• Decomposer
• Carbon Sink
• Biogeochemical Cycles!!!
• PROBLEM Erosion

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Soil Triangle and Example
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Clay soils- high percentage of clay

• Come from rocks with a lot of feldspar
• Hold a lot of water
• Doesnt drain well

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Silty soils

• Very fine particles, have a gritty feel
• Erodes easily
• Often found on riverbanks

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Sandy soils- high percentage of sand

• Come from weathered granite and rocks with a lot
  of quartz
• Doesnt hold water, drains quickly

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Transported vs. Residual soil

• Transported soil moved from original location,
  will have a different composition than the
  bedrock below
• Residual soil soil that rests on top of its
  parent rock

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Soil profile

• Cross-section of layers of soil and the bedrock
• beneath

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Horizons (Residual Soil)

• A horizon topsoil
• B horizon subsoil (minerals, clay, humus)
• C horizon partially weathered bedrock
  (regolith)
• O- Organic
• E- no organics
• R- bedrock
• Top 2 layers-bacteria, fungi, worms, insects

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• Transported soils DO NOT have horizons, they are
  found in layers or unsorted depending on how they
  were transported!

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Soil and Climate

1. Humid tropical climates a lot of rain high
   temps chemical weathering
2. Desert climates minimal rain, high temps
   minimal weathering
3. Temperate climates temperature range between
   cool and warm, rainfall varies both types of
   weathering

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Tropical Soils

• Laterites Thick but infertile soils produced in
  tropical climates
• Contains irons and other minerals that do not
  dissolve
• Topsoil often thin
• Organic matter
• constantly added

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Desert Soils

• Thin
• Made up of mostly rock fragments (evidence of
  mechanical weathering)
• Arctic soil similar

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Temperate Soils

• All three horizons can reach a thickness of
  several meters.
• 2 main types
• 1. pedalfer- contains clay, quartz, and iron
  compounds, forms in places receiving 65cm of
  rain per year (Ex. states east of Mississippi and
  Gulf Coast states)

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• 2. pedocal- contains large amounts of calcium
  carbonate, formed in places receiving less than
  65 cm of rain per year.

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Soil types around the world correspond to
climates
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Topography and Soil

• Too flat poor drainage
• On slopes- soil is thick and fertile at the
  bottom and thin and nutrient-poor on the slope.
• Ideal soil conditions fairly flat but with good
  drainage

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