Which horizon is primarily composed of organic matter and forms the surface layer in soil profiles?

• A. O Horizon
• B. C Horizon
• C. B Horizon
• D. A Horizon

Answer: (A)

The surface layer dominated by organic matter is the organic horizon. It consists of plant and animal residues in various stages of decomposition, from fresh litter to humus, and sits at the very top of the soil profile where organic material accumulates. This horizon is distinct because its composition is mainly organic matter rather than mineral particles, unlike the mineral horizons below. The A horizon is the mineral topsoil that contains some organic matter mixed in, the B horizon is a subsoil enriched with transported ions and clay, and the C horizon is the weathered parent material. So the horizon primarily composed of organic matter forming the surface layer is the organic horizon.