* Decomposition: The A horizon is where most organic matter, like dead leaves, roots, and animal remains, decomposes. This process is carried out by microorganisms like bacteria and fungi.
* Humus Formation: Decomposition leads to the formation of humus, a dark, stable, and highly fertile substance that improves soil structure, water retention, and nutrient availability.
* Root Activity: The A horizon is the zone where most plant roots grow, further contributing to biological activity and mixing of organic matter.
While other horizons may also contain evidence of biological activity, the A horizon is where it is most concentrated and visible.
