Soil Identification

  1. Identification is based upon the soil profile.
  2. Soils develop horizons
    1. recognizably different layers that are parallel to the surface
    2. horizons form :
      1. because of differences in weathering
      2. accumulation of organic materials
      3. movement of inorganic materials
    3. horizons form the soil profile
  3. There are currently about 15,000 defined soils in the United States.
  4. Soils are usually named for the first location where they were sampled and described.
  5. On Whidbey Island we have 80 unique soils. Examples:
    Name Parent material Ave. bushels of wheat/acre
    Coupeville loam marine or lake sediments 65
    Hoypus loamy sand glacial gravelly drift 10
    Lummi silt loam marine sediments n/a
    Puget clay loam fine textured stream deposits 55
    Whidbey sandy loam cemented gravelly till 18
  6. Identifying the soil will determine Best Management Practices (BMP) for that soil.

Soil texture:

  1. Texture is an important physical property (other properties are color, structure, density)
  2. Texture is the relative proportions of sand, silt and clay in a soil
  3. When determining soil texture, particles larger than 2 mm are excluded, as is organic matter

USDA classifications of soil particles

Class Size Characteristics
sand 2.0 - 0.05 mm round or irregularly shaped, not sticky or plastic, low water holding ability
silt 0.05 - 0.002 mm irregular shaped, plastic and cohesive
clay < 0.002 mm usually plate-like, sticky and plastic, high surface area to mass ratio, high water holding ability, greatly influences soil properties