What is a common feature of the A horizon concerning its organic composition?

The A horizon is a key layer in the soil profile, predominantly recognized for its significant organic composition. It is often referred to as the topsoil, where the accumulation of organic matter from decomposed plant materials leads to the presence of humus. This humus enriches the soil, contributing to its fertility and ability to retain moisture, which are essential for plant growth. The presence of humus also enhances the soil's structure and nutrient availability, making this layer crucial for supporting various forms of life.

In contrast, the other options do not accurately describe the A horizon. While some minerals may be present, the defining characteristic of the A horizon is its rich organic matter rather than high mineral content. The notion of little to no organic matter contradicts the very essence of this layer, which is defined by its organic richness. Similarly, while stony soils may exist in different contexts, the A horizon is typically where finer particles and organic materials dominate rather than a stony composition. Thus, the emphasis on humus effectively captures the A horizon's significance within the soil profile.