- Identification is based upon the soil profile.
- Soils develop horizons
- recognizably different layers that are parallel to the surface
- horizons form :
- because of differences in weathering
- accumulation of organic materials
- movement of inorganic materials
- horizons form the soil profile
- There are currently about 15,000 defined soils in the United States.
- Soils are usually named for the first location where they were sampled and described.
- 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
- Identifying the soil will determine Best Management Practices (BMP) for that soil.
- Texture is an important physical property (other properties are color, structure, density)
- Texture is the relative proportions of sand, silt and clay in a soil
- When determining soil texture, particles larger than 2 mm are excluded, as is organic matter
USDA classifications of soil particles
|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|