Subsoil

Like topsoil, it is composed of a variable mixture of small particles such as sand, silt and clay, but with a much lower percentage of organic matter and humus.

Because it has less organic matter than topsoil, subsoil soil colour is mainly derived from iron oxides.

Due to physical, chemical, and biological activity, the subsoil generally has a soil structure.

Clay-based subsoil has been the primary source of material for adobe, cob, rammed earth, wattle and daub, and other earthen construction methods for millennia.

Although not sterile, subsoil is relatively barren in terms of soil organisms compared to humus-rich topsoil.