What Is a Soil Horizon?
A soil horizon is a distinct layer of soil, parallel to the ground surface, with unique physical, chemical, and biological characteristics that differ from the layers above and below it. These layers are formed over long periods through processes like weathering, the decay of organic matter, and the movement of minerals.
Section 2: The Master Horizons
The primary soil horizons are typically labeled with letters. The O horizon is the top organic layer of fresh and decaying plant matter. The A horizon, or topsoil, is a mix of minerals and decomposed organic material. The B horizon, or subsoil, is an accumulation zone for minerals washed down from above. The C horizon consists of weathered parent material, and the R horizon is the underlying solid bedrock.
Section 3: A Practical Example of a Soil Profile
Imagine digging a deep pit in a forest. At the very top, you'd find the O horizon (leaves and twigs). Just below is the dark, nutrient-rich A horizon (topsoil). Further down, the B horizon might be a denser, clay-rich layer with a reddish color. Below that, the C horizon would look like broken, weathered rock, which sits on top of the R horizon (bedrock). This entire vertical sequence of horizons is called the soil profile.
Section 4: Why Are Soil Horizons Important?
Understanding soil horizons is vital for agriculture, environmental science, and construction. Farmers analyze horizons to manage soil fertility and irrigation. Geologists use them to understand an area's geological history and landscape development. Engineers must consider the properties of different horizons when designing foundations for buildings and roads.