Soil Profile

The soil is the topmost, dark brown layer on the earth’s crust which is mainly composed of organic materials and rock particles mixed with minerals and other organisms which support life. A soil profile is a vertical cross-section of the soil. There are various a series of horizons or layers of soil. Each horizon of soil may be different in both physical and chemical ways.

Before moving onto the Soil Profile, let us have a quick glance about the soil.

What is Soil?

The soil is the small granules that cover the surface of the earth. It is the surface out of which plants grow and are mainly composed of organic and inorganic material. It takes thousands of years for soil formation and is mainly formed by the breakdown of rocks through the action of wind, water, temperature, and climate. There are various types of soil and they include clay, loam, silt, sand, etc.

Soil Profile

Soil Profile

Soil Profile

The soil is found in layers, which are arranged during the formation of soil. These layers called horizons, the sequence of layers is the soil profile. The layers of soil can easily be observed by their color and size of particles. The main layers of the soil are topsoil, subsoil and the parent rock. Each layer has its own characteristics.

The vertical section of the soil that is exposed by a soil pit is termed as the soil profile. A soil pit is a hole that is dug from the surface of the soil to the underlying bedrock.  Soil profile plays a very important role in determining the use of the soil. It helps one to differentiate the given sample of soil from other soil samples based on factors like its color, texture, structure, and thickness, as well as its chemical composition.

Horizons of the Soil

The soil profiles are composed of a series of horizons or layers of soil stacked one on top of the other like layers in a cake. These horizons, identified by letters, A, B, C, and O.

The O-Horizon

The O horizon is the upper layer of the topsoil which is mainly composed of organic materials such as dried leaves, grasses, dead leaves, small rocks, twigs, surface organisms, fallen trees, and other decomposed organic matter. It contains about 20 to 30% of organic matter. This horizon of soil is often black brown or dark brown in color and this is mainly because of the presence of organic content.

The A-Horizon or Topsoil

It is also called the humus layer, which is rich in organic material. This layer consists of both organic matter and other decomposed materials. The presence of humus makes the topsoil soft, porous to hold enough air and water. In this layer, the germination of seeds takes place and new roots are produced which grows into a new plant. Many living organisms like earthworms, millipedes, and centipedes, bacteria, and fungi are found in this layer of soil.

The B-Horizon or Subsoil

It is the subsurface horizon, present just below the topsoil and above the Bedrock. It is comparatively harder and compact than topsoil. It contains less humus, soluble minerals, and organic matter. It is a site of deposition of certain minerals and metal salts, including the iron oxide in a large proportion. This layer holds enough water than the topsoil and is lighter brown due to the presence of clay soil. Farmers often mix horizon-A and horizon-B when ploughing their fields.

The C-Horizon or Bedrock

Bedrock is also known as parent rock and lies just below the subsoil. It is very hard as it is completely made up of stones and broken bedrock rocks. This layer contains no organic matter and represents a transition zone between the earth’s bedrock and horizon A and B.

Stay tuned with BYJU’S to learn more about the soil, its profile, and its properties.

Practise This Question

What is the importance of humus?