Which soil layer is the uppermost mineral layer in a soil profile?

Which soil layer is the uppermost mineral layer in a soil profile?

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

Answer: (A)

In a soil profile, the surface may be covered by an organic layer of decomposed matter, but the first layer that is mainly mineral material is the topsoil. This layer, called the upper mineral layer, sits below the organic surface and above deeper mineral layers. Humus belongs to the organic portion of the soil—it's decomposed organic matter—and is not itself a mineral layer. Below the topsoil is the subsoil, a deeper mineral layer, and further down are the parent material and bedrock. So, the uppermost mineral layer is topsoil.

In a soil profile, the surface may be covered by an organic layer of decomposed matter, but the first layer that is mainly mineral material is the topsoil. This layer, called the upper mineral layer, sits below the organic surface and above deeper mineral layers. Humus belongs to the organic portion of the soil—it's decomposed organic matter—and is not itself a mineral layer. Below the topsoil is the subsoil, a deeper mineral layer, and further down are the parent material and bedrock. So, the uppermost mineral layer is topsoil.