Which soil horizon typically contains the most nutrients?

The O horizon is often referred to as the organic horizon and is typically composed of organic material such as decomposed leaves, plant matter, and other organic residues. This layer is vital for nutrient availability because it is rich in nutrients that are essential for plant growth. Decomposition processes in the O horizon result in the formation of humus, which enhances the nutrient-holding capacity of the soil, improves soil structure, and contributes to the soil's fertility.

The organic matter in the O horizon not only provides important nutrients directly but also promotes microbial activity, further aiding in the breakdown of materials and nutrient cycling. This makes the O horizon an important source of nutrients compared to the other soil horizons.

In contrast, the C horizon contains parent material from which the soil develops and generally has low nutrient content. The B horizon is where minerals leached from the above horizons accumulate, and while it can contain some nutrients, it is often less nutrient-rich than the O horizon. The E horizon typically experiences significant leaching of minerals and nutrients, resulting in lower nutrient availability.