Which soil layer has the most organic matter?

Which soil layer has the most organic matter?

• A. Top mineral layer
• B. Humus layer
• C. Subsoil
• D. Gravel layer

Answer: (B)

The most organic matter is found in the humus layer because that part of the soil is built up from decomposed plant and animal material. Microbes and other soil life actively break down litter in this layer, turning it into stable humus that darkens the soil, improves structure, and holds nutrients and water. The top mineral layer has some organic material mixed in, but it’s mostly mineral particles. The subsoil contains less organic matter and is lower in biological activity, while the gravel layer is mainly rock fragments with very little organic content.

The most organic matter is found in the humus layer because that part of the soil is built up from decomposed plant and animal material. Microbes and other soil life actively break down litter in this layer, turning it into stable humus that darkens the soil, improves structure, and holds nutrients and water. The top mineral layer has some organic material mixed in, but it’s mostly mineral particles. The subsoil contains less organic matter and is lower in biological activity, while the gravel layer is mainly rock fragments with very little organic content.