Introduction to Soils

Understanding soils requires many scientific disciplines including physics, chemistry and biology.

A soil is:

1. a three dimensional,
2. dynamic,
3. natural body,
4. a product of the environment under which it is developing.

Uses for soils include

1. A medium for plant growth (crops, range and forest): support, oxygen for roots, adequate temperature, water and nutrients
2. Environmental - water quality, retaining pollutants.

Three Components of a Typical Soil:

1. 45% Inorganics (minerals)
2. 5% Organics
3. 50% Pore space for air and water

Factors In Soil Formation (PCOTT):

1. Parent materials - residual (rock weathered by physical and chemical processes), transported and organic materials.
2. Climate - moisture and temperature.
3. Organisms - animals and vegetation.
4. Time - duration, intensity of processes.
5. Topology - affects water distribution, adjustment of parent materials, temperature (exposure).

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