What does the 'B' horizon in soil composition represent?

The 'B' horizon, commonly referred to as the subsoil, plays a critical role in soil composition and development. It is located beneath the 'A' horizon (topsoil) and above the 'C' horizon (parent material). The 'B' horizon typically accumulates minerals leached down from the upper layers, as well as organic materials that have broken down, contributing to its nutrient content. This accumulation leads to a denser and often more compact layer, which can strongly influence plant growth by providing essential nutrients and a barrier for root development. The composition of the 'B' horizon varies based on the soil type and its environment, which further emphasizes its importance in overall soil health and function.

In contrast, the topsoil, which is represented by the 'A' horizon, primarily consists of organic matter and is the most fertile region of the soil, making it critical for seed germination and plant growth. Organic matter, while also found throughout the soil profile, is particularly concentrated in the topsoil rather than in the subsoil. The 'C' horizon consists of weathered rock or unconsolidated material that provides the foundation for soil formation but lacks the characteristics of developed soil horizons.