What are soil horizons?

Soil horizons are horizontal layers of soil. Each layer has a distinct name that is distinguished by a particular letter. The contents of each layer vary.

Six basic soil horizons exist: O, A, E, B, C and R. The O horizon is the topmost layer and contains leaf litter and decomposing matter. Horizon A is known as the topsoil. It is where seeds germinate and plants grow. Horizon E does not contain many minerals and is lighter in color. Horizon B is also known as subsoil and contains mineral deposits. Very little organic matter is found in the C horizon. The R horizon is the last layer that rests beneath all other layers.