What is Soil?
Soil is the mineral and organic material on the surface of the earth that serves as a natural medium for the growth of plants and the base for man's activities.
Soil is a dynamic medium, which has formed over time and continues to do so. It takes up to 500 years or more, to make 1 inch of soil. Physical, chemical and biological processes (like weather, temperature and animal activities), break down parent material (from original rock) into soil. In Michigan, glacial activities had a major influence on soil development.
Soil is important to man
Soil produces food, fiber, shelter, fuel. Soil provides a base or surface for roads, buildings, walking, all man's activities.
Soil composition
- 45% Mineral Matter (from rocks)
- 5% Organic Matter (dead & living plant/animal material)
- 25% Air
- 25% Water
Soils are combinations of SAND, SILT and CLAY particles classified by size
- SAND: large, gritty, minerals resistant to weathering.
- SILT: much smaller size, smooth, fine textured.
- CLAY: smallest size, very porous and readily holds water, sticky when wet, extremely active chemically. Clay test: hold a moist ball of soil in your hand. Squeeze the ball and try to form a flat ribbon of soil between your thumb and finger. The more your ribbon holds together, the more clay the soil has in it.
- OTHER: HUMUS (decomposing organic matter), a stable, long lasting material. Humus improves soil by increasing aeration and water and nutrient retention capacity.
There are thousands of different kinds of soil. Factors which cause soils to differ from each other include color, texture (sand, silt, clay), stoniness, wetness, slope, amount of organic matter and soil permeability or how well water moves through the soil.
Soil horizons
Over time, soil forms layers (horizons) in the following broad categories:
- TOPSOIL: dark color, nicely textured, high organic matter content, very important to plant growth.
- SUBSOIL: below topsoil horizon, has accumulated elements from topsoil, but only minor amounts of organic matter.
- PARENT MATERIAL: unconsolidated rock material below the subsoil, the material directly broken down into soil.
- BEDROCK: solid rock below parent material.
Want to know what kind of soil you have on your property, your school grounds or some other location? Check out a Washtenaw County Soil Survey at the Conservation District Office.
Other soils data
To access, query, analyze, and download reports from various national soils databases, visit the Michigan USDA Natural Resources Conservation Service, National Soil Survey Center.