Soils

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Soils

• Earths Changing Surface

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Review

• Weathering breaks down rock
• Mechanical
• Chemical
• Erosion removes the rock particles

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What is soil?

• The loose, weathered material on Earths surface
  in which plants can grow.

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Soil

• Bedrock - the solid layers of rock beneath soil.

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Soil Composition

• Mixture of rock particles, minerals, decayed
  organic material, water, and air
• Humus decayed organic material in soil

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Soil

• Fertility of Soil measures how well the soil
  supports plan growth.
• Rich in humus has high fertility
• Why does fertility of soil matter?

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Soil Texture

• What does soil feel like?
• Sand feels coarse and grainy
• Clay feels smooth and silky
• Soil texture depends on the size of soil
  particles.

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Soil Particle size
Clay Silt Sand Gravel
Less than 1/256 mm Less than 1/16 mm Less than 2 mm 2 mm and larger
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Loam

• Soil that is made up of about equal parts of
  clay, sand, and silt is called loam.

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Soil Formation

• Forms as rock is broken down by weathering and
  mixes with other materials on the surface.

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Soil Formation

• Soil Horizons
• A layer of soil that differs in color and texture
  from the layers above or below it.

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Soil Horizons
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A Horizon

• Topsoil a crumbly, dark brown soil that is a
  mixture of humus, clay, and other minerals.
• Develops as plants add organic material to soil
  and plants weather rock.

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B Horizon

• Subsoil clay and other particles washed down
  from the A horizon, but little humus.

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Soil Types

• Thousands of different types of soil in U.S.
  alone
• Classified based on climate, plants, and soil
  composition.

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Living Organisms in Soil

• Some soil organisms make humus
• Some soil organisms mix the soil and make spaces
  in it for air and water.