The B horizon in a soil profile is also known as which?

• A. Topsoil
• B. Subsoil
• C. Bedrock
• D. Humus

Answer: (B)

In a soil profile, layers tell the story of how soil forms and moves materials. The layer called subsoil is the B horizon, sitting beneath the topsoil. It forms as minerals and fine particles like clay and oxides of iron and aluminum move down from above and accumulate here (a process called illuviation). Because of this, the B horizon often has less organic matter than the surface horizon and can be more compact, with a color that reflects the accumulated oxides. It sits above the underlying parent material and below the nutrient-rich topsoil. By contrast, the topsoil is the A horizon rich in organic matter, bedrock refers to the solid rock beneath all soil layers, and humus is the decomposed organic material typically found in surface layers.