What layer of soil is referred to as topsoil?

Topsoil is primarily identified as the A Horizon in soil profiles. This crucial layer is typically rich in organic material, nutrients, and microorganisms, making it vital for plant growth. The A Horizon is characterized by its dark coloration, which results from the accumulation of organic matter, such as decomposed plant and animal material.

This layer acts as a reservoir for moisture and nutrients, directly influencing agricultural productivity and natural vegetation. Its composition and structure allow for better water retention and root penetration, supporting the growth and sustainability of plants.

In contrast, the other layers mentioned each have distinct characteristics. The O Horizon, primarily composed of organic matter such as decomposed leaves and other plant material, overlays the A Horizon but is generally less extensive. The B Horizon, often referred to as the subsoil, is located beneath the A Horizon and is typically denser, with fewer nutrients and organic materials. The subsoil plays different roles, mainly related to water retention and mineral storage, rather than rich nutrient supply for plant roots. Understanding these distinctions provides clarity on the importance of the A Horizon as the topsoil layer essential to ecosystem health and agricultural practices.