Sub soils refer to the underlying layer of soil that lies beneath the topsoil. There are several synonyms that can be used for sub soils such as subsoil, substratum, lower soil, subterranean soil, and subsoil layer. These terms are commonly used in geology and agriculture research. The substratum is a layer of soil or rock that underlies the topmost layer of earth. The subterranean soil is the soil that lies beneath the surface and is not visible from above. The subsoil layer refers to the soil layer which is situated just below the topsoil and has a distinct texture and character from the overlying layers. Regardless of the term used, subsoils play an essential role in supporting plant growth and maintaining the soil structure.