Subsoil
This is the layer below the top soil which is usually less fertile and of poorer texture.
The subsoil usually looks pale because of its low fertility. It is sometimes hard and compacted and stops water draining away, creating waterlogged conditions that slow down plant growth or cause root diseases. Subsoil often contains valuable minerals that can be tapped by growing deep-rooting plants such as alfalfa or fenugreek and adding them to the compost heap. They help to break up the subsoil, as does deep digging. Because of its poor quality, never leave subsoil on the surface.