Which soil horizon is the organic surface litter layer?

• A. A horizon (top mineral horizon with humus)
• B. E horizon (eluviation horizon)
• C. O horizon (organic surface litter)
• D. B horizon (illuvial subsoil with accumulations)

Answer: (C)

The organic surface litter layer is the O horizon. It sits on the very top of the soil profile and is composed mainly of fresh and partially decomposed plant and other organic material that hasn’t mixed into the mineral soil yet. That’s why it appears darker and feels more like litter than mineral soil.

The A horizon is the top mineral layer where organic matter has mixed with minerals, giving some humus and a darker color but still primarily mineral. The E horizon is a leached zone where certain materials have been washed out, often lighter in color. The B horizon lies below, where materials like clay and oxides have accumulated (illuviation).