5.2. Soil Horizons

A vertical section of soil from the surface down to the bedrock consisting of many layers is collectively known as soil profile. These different sections are called soil horizons. We can easily observe different horizons in a mine or roads dug under the ground. The recognition of different soil horizons is based on the physical and chemical characteristics of soils. Scientists have divided the soil into three main horizons (figure 23). ‘Horizon A’ is the topmost zone, where organic materials have got incorporated with the mineral matter, nutrients and water, which are necessary for the growth of plants. ‘Horizon B’ is a transition zone between the ‘Horizon A’ and ‘Horizon C’, and contains matter derived from below as well as from above. It has some organic matter in it, although the mineral matter is noticeably weathered. ‘Horizon C’ is composed of the loose parent material. This layer is the first stage in the soil formation process and eventually forms the above two layers. Underneath these three horizons is the rock which is also known as the parent rock or the bedrock.