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.
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 colour 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 colour, texture, structure, and thickness, as well as its chemical composition.
Also refer: Minerals In The Soil And Soil Pollution
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 colour 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.
Explore more about: Preparation of Soil for Agriculture
- 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.
Frequently Asked Questions on Soil Profile
What is Soil Profile?
The soil profile is a vertical section of the soil that depicts all of its horizons. The soil profile extends from the soil surface to the rock material.
How is Soil Formed?
Soil is mainly formed by the breakdown of bigger rocks into smaller and fine particles with the continuous action of wind, rain and other agents of natural force. It takes hundreds to thousands of years for the formation of soil.
What are the basic components of Soil?
Air, water, minerals and other organic matter are the basic components of soil.
What is the importance of Soil Profile?
The soil profile plays an important role in maintaining the fertility of the soil and the nutrition content in the soil.
What are the horizons of soil?
The soil profiles are composed of a series of horizons or layers of soil, which are stacked one above the other. The 4 horizons of soil are:
What is Topsoil?
The topsoil is the topmost layer of the soil. It is dark brown coloured soil which mainly consists of organic matter, decomposed material and many living organisms including some microbes, earthworms and other worms.