The Soil Profile

When most people think of soil, they generally tend to consider only the surface of the land. In fact, this is only the topsoil. Soil may go down several metres before solid rock is reached. There are actually three main layers in most soils (referred to as horizons). These are the topsoil, subsoil and then the parent material.



The nature of soils varies according to geographical location, climate, etc. However, the topsoil will often be dark brown or black in colour (though not in very arid or dry areas), and is made up of rock material that has been chemically and physically broken down and changed, and mixed with organic materials such as dead plants, particularly roots of them. Furthermore, it will generally be full of plant and animal life.

The subsoil also consists of altered rock material, but contains much less plant life (mainly roots) and living creatures. However, minerals can be broken down, and nutrients released from this layer for use by roots of plants.

Finally, the parent material is located at the very bottom, usually below half a metre and consists mostly of unaltered rock or glacial deposits, the matter from which the soil is developed.