Erosion involves the transportation of weathered pieces of rocks and materials. Therefore the weathered rocks, soil, and materials are moved from their original location to another location. Gravity, running water, wind, glaciers, and ocean currents are some of the major agents of erosion. The development of soil usually begins when weathered rocks are broken down into sediments and mix with water, air, and humus.
- You can read the first paragraph here about soil profile.
- Watch this about Soil Texture.
- Watch this about Erosion.
Soil formation occurs as the result of the interactions of several important factors: parent material, time, climate, organisms, and slope. Parent material is the geologic material and mineral matter on which soil forms. Soil that forms on bedrock is referred to as residual soil. Soil that forms on unconsolidated deposits is referred to as transported soil. Various factors such as the rate of weathering, the rate of soil formation, and soil fertility are affected by the parent material. Over the course of time the depth of the soil above the parent material increases. Therefore, the longer soil has been forming the deeper the soil will be. Climate influences the type of weathering, the rate of the weathering, and therefore the depth of the soil. The amount of precipitation has an impact on soil fertility because if influences how quickly nutrients are removed from the soil. Organisms have a tremendous impact on the properties
of soil. Most of the organic matter in soil comes directly from plants. Minerals and organic matter in the soil are mixed and redistributed by burrowing organisms. Organisms also play a large role in the nitrogen cycle. Nitrogen fixing bacteria in the soil helps convert nitrogen from the atmosphere into ammonia. This is important because plants need nitrogen, which is very necessary for plant growth.
Soils have variations in the following key properties: composition, texture, structure, and color. The variations in these factors result in soil being divided into horizontal zones known as soil horizons. The A Horizon is the uppermost layer of the soil and is most commonly referred to as topsoil. It is composed primarily of organic matter with the lower portion of this horizon being mostly mineral matter and organic matter. The B Horizon is most commonly referred to as subsoil. It consists of fine particles of clay that have washed down from the A horizon. The C Horizon consists primarily of parent material that has been partially weathered. In mature soil, there is also an O horizon. It located above the A horizon and it consists of organic material.
The three common types of soil are pedalfer, pedocal, and laterite. Pedalfer is normally found in temperate areas with high annual precipitation. Pedocal is normally found in areas with dry climates – often grasslands and savannahs. Laterite forms in tropical climates with high temperature and precipitation. Read the article located on the sidebar to learn more about soil erosion.
Match the horizons with the soil types.
| A horizon | weathered bedrock | ||
| B horizon | subsoil | ||
| C horizon | humus and leaf litter | ||
| O horizon | topsoil |
Click here to reveal the answers.
A horizon = topsoil, B horizon = subsoil, C horizon = weathered bedrock, O horizon = humus and leaf litter