Which horizon is referred to as topsoil?

The horizon referred to as topsoil is known as the A horizon. This layer is crucial for plant growth because it is rich in organic material, nutrients, and microorganisms that contribute to soil fertility. The A horizon typically contains a mixture of decomposed organic matter and mineral particles, which enhances its ability to retain water and support root systems.

In contrast, the O horizon consists mainly of organic matter such as decomposed leaves and plant material, primarily found in forested areas. The B horizon, often called the subsoil, accumulates clay, minerals, and nutrients that leach down from the layers above it, but it generally lacks the organic material and biological activity found in the topsoil. The C horizon is composed of weathered rock and parent material and is deeper in the soil profile, typically lacking the characteristics that are important for supporting plant life. Thus, the A horizon is uniquely positioned to provide the necessary resources for healthy plant growth, confirming it as the topsoil layer.