All About Soil

Soil Formation Soil is formed from weathered rock fragments, so the type of soil depends on the parent rock (the source of the rock fragments). If soil stays above the bedrock from which it was formed, it is called residual soil. If it is moved, it is called transported soil.

What is Soil? Soil is the topmost layer of the Earth’s Crust. It is a mixture of minerals, rock particles, water, and organic material that can support plant life.

Humus Humus is the dark organic layer of topsoil formed from decaying plant and animal matter. Humus is important because it contains nutrients and holds water.

Loam Loam is a mixture of soil types (clay, silt, and sand). It is good for growing plants because it allow the correct amount of water and air through.

Rate of Soil Formation Soil formation is affected by the rate of weathering in different climates. Some influences include temperature and moisture. Example: Weathering occurs faster in hot wet climates

Plants, Animals, & Soil Plants leach nutrients from the soil. Because of this, farmers must use cover crops or crop rotation to return nutrients to the soil. Animals that burrow in the soil cause weathering as they upturn new rock pieces. Some animals such as worms return nutrients to the soil.

Soil Horizons

A Horizon This is the topsoil layer, and it contains the most humus. This is the layers where the most leaching occurs.

E Horizon This is the eluviation layer where there most leaching of nutrients occurs.

B Horizon This is the subsoil layer. Nutrients and dissolved substances from the top layers are deposited here.

C Horizon This is the layer of parent material. It is made up of partially weathered bedrock.

R Horizon This is bedrock. There is little or no weathering here.