Notes on Soil Formation (Use pages 186-192 in your textbook and the power point online.)

Soil is a mixture of______, ______, ______, ______, and water

Soil is formed when rock is broken down by ______and mixes with other materials on the surface

a)______is formed whenever bedrock is exposed. Bedrock is the solid layer of rock beneath the soil. Weathered rock is composed of sand, ______and ______.

b)______is a dark-colored substance that forms and plant and animals remains decay. Humus makes soil more fertile (soil that is rich in nutrients and can support good plant growth.

Soil texture

  • sand is coarse and ______; clay is silky smooth but very ______.
  • particles of rock in soil are classified by size;
  • ______- largest particles ( from pebbles to boulders)
  • sand- next largest
  • ______- next largest
  • ______- smallest particles

loam- soil that is made up of about equal parts of______; crumbly in texture; holds in both air and water so best for growing plants

soil is formed more quickly in warm, moist environments because ______occurs more quickly there

Soil horizons

  • definition- a layer of ______that differs in texture from the layers above and below it
  • horizon A- made up of ______( a crumbly, dark brown soil that is a mixture of humus, clay and other minerals)
  • horizon B-called the ______; consists of clay and other particles washed down from the A horizon, but has little humus
  • horizon C- contains only partly ______.

Soil organisms

  • litter- loose layer of ______(leaves, stalks) falls on the soil’s surface
  • decomposers-organisms that break the remains of dead organisms into smaller pieces and digest them with chemicals. This is the process by which ______is formed.
  • ______- microscopic organisms that cause decay. They attack dead organisms and their wastes in soil
  • earthworms- eat their way through soil and carry ______down with them into the subsoil and ______back to the surface of the soil; they pass the soil they eat as waste which enriches soil with nitrogen and other substances that help ______grow; they ______the soil by mixing air into it that plant’s roots need.
  • burrowing animals- also break up soil and mix humus into it as well as add nitrogen and organic material when they ______; they also aerate the soil

Soil processes

Desertification- the advance of ______conditions into areas that once were fertile; ______is one cause (ex: drought causes crops to fail and die; then they fail to provide ground cover and wind erodes the soil away)

Dust Bowl- ______(thick mass of tough roots at the surface of the soil) in the Great Plains states was plowed under to grow crops. Soil dried out without the sod to help hold in moisture, turned to dust and blew away