There are distinct layers that make up any given soil sample in a natural habitat. These layers lie on each other, and they are also in a parallel position to the surface of the soil. A soil horizon then refers to each of these unique layers. When these layers are viewed vertically and in a cross-sectional manner, they form what is known as the soil profile. The top layer of the soil is called the “O” horizon, and it consists of dead and decomposed organic matter, which is rich, still decaying, and mainly made up of humus.
The “A” horizon then follows below the above layer and is usually rich in nutrients. The “E” horizon is mainly composed of silt and sand and is light in color. The “sub-soil” constitutes the “B” horizon which is also rich in essential minerals like aluminum. Under the “B” horizon are the large rocks, which are sometimes partially broken and are found in the layer called the “C” horizon. The weathering process does not easily affect this layer because it is deeply underlying. Finally, the “R” horizon constitutes the bedrock. There are no boulders at this point but heavy deep underlying bedrocks that are equally difficult to penetrate.