Which of the following describes A-horizon soil?

The A-horizon, commonly known as topsoil, is the uppermost layer of soil that is rich in organic material and nutrients. This layer is crucial for plant growth as it contains most of the soil's biological activity, including microorganisms, earthworms, and plant roots. The composition of the A-horizon typically includes a mix of mineral particles and organic matter, which contributes to its dark color and increased fertility compared to lower layers.

Topsoil is vital for agriculture and natural ecosystems because it supports vegetation and retains moisture, while also playing a key role in carbon storage and soil health. The presence of organic matter is what distinguishes the A-horizon from other soil layers, making it essential for environmental sustainability and crop production.

The other options describe different soil layers or characteristics that are not applicable to the A-horizon, reinforcing its unique role as the top layer rich in nutrients and organic content.