Define “soil horizon.”

A soil horizon is defined as a distinctive layer of soil that has unique properties distinguishable from the layers above and below it. This definition captures the essence of how soil is structured and categorized in soil science. Each horizon can vary in color, texture, composition, and biological activity, which are influenced by factors such as mineral content, organic matter, and environmental conditions, including climate and vegetation.

Understanding soil horizons is crucial for soil management, conservation, and agricultural practices since each layer plays a specific role in the ecosystem. For example, the topmost horizons typically contain more organic material, while deeper layers may be more mineral-dense. This unique layering allows for a variety of functions, such as water retention, nutrient cycling, and habitat creation for organisms.

The other choices provided do not fully encapsulate the concept of a soil horizon. For instance, a mixture of soil and organic matter refers to components of soil rather than characterizing a specific layer. A layer characterized by high permeability is too specific to be broadly applicable, as it does not acknowledge the defining features of all horizons. Lastly, designating a soil horizon solely as a topsoil layer overlooks the complexity and variety present in the different layers of soil profiles. Therefore, acknowledging the unique characteristics that