How do soils form?

• five major factors control how a soil forms.

  These factors are:

  • CLimate,
  • ORganisms,
  • Relief (landscape),
  • Parent material, and
  • Time.

  That is CLORPT for short!
• Climate- Temperature and Moisture influence the speed of chemical reactions, which in turn, control how fast rocks weather and dead organisms decompose.
• Soils develop fastest in warm, moist climates, and slowest in cold and arid ones.
• Organisms - Plant roots spread out, animals burrow, and bacteria eat. These and other soil organisms speed up the breakdown of large soil particles into smaller ones.
• Organisms

  Roots are a powerful soil-forming force, cracking rocks as they grow. And roots produce carbon dioxide that mixes with water and forms an acid that wears away rock.
• Names of Slope Locations

  • SUMMIT (top of slope)
  • SHOULDER
  • BACK-SLOPE
  • FOOT SLOPE
  • TOE SLOPE
  • DRAINAGE WAY (Bottom of Slope)
• Color can tell us about how a soil “behaves”. A soil that drains well is brightly colored. One that is wet and soggy has an uneven (mottled) pattern of grays, reds, and yellows.
• Parent Material

  • Just like you inherited some characteristics from your parents, every soil inherits traits from the material from which it formed.
• • Soils that form in limestone bedrock are rich in calcium,
  • Soils that formed from materials at the bottom of lakes are high in clay.
• • Transported materials

  • Bedrock or residual material

  • Organic materials
• Transported Sediments

  • Water transported or deposited

  – Marine

  – Fluvial

  – Lacustrine
• Transported Sediments

  • Windtransported

  – Aeolian (loess)
• Transported Sediments

  • Gravity transported

  – Colluvium
• Transported Sediments

  • Ice transported

  – Glacial
• Marine

  • Deposited in a marine environment

  • Variable texture dependent on energy of depositional environment

  – Low energy – fine textured

  – High energy – coarse textured
• Fluvial

  • Sediments deposited in rivers or floodplains

  • Texture coarsest near active channel
• Bedrock or Residual Material

  • Properties related to mineral present in parent rock and weathering

  – Clay mineralogy

  – Inherent fertility

  • Particle size variable
• Time

  • Older soils differ from younger soils because they have had longer to develop
• In the Northern U.S., soils tend to be younger, because glaciers covered the surface during the last ice age, which kept soils from forming. In the southern U.S., there were no glaciers. There, the soils have been exposed for a longer time, so they are more weathered.
• Each soil has its own history.

  -Charles Kellogg, Former Director, Soil Survey Division, USDA