What is the primary characteristic of Horizon O in soil profiles?

The primary characteristic of Horizon O in soil profiles is that it is a layer of organic material found at the surface of the soil. This horizon is crucial for several reasons; it is typically where organic matter, such as decomposed leaves, plant material, and other organic debris, accumulates, creating a rich, nutrient-dense layer. This organic layer is essential for soil fertility, as it contributes significantly to the biological activity in the soil, providing food for microorganisms and enhancing the soil structure.

Horizon O plays a vital role in supporting plant growth by retaining moisture and nutrients, thus fostering a healthy ecosystem. The presence of this organic layer indicates a well-developed soil profile, often associated with forested or grassland areas, where decomposition processes are active and contribute to soil health.