Soil Profile: Content, Composition, and Importance

Soil Profile: The soil which we stand on, gives us many more things than we can even think of. It is an essential part of nature. The topmost, organic layer of the earth rich in minerals and microorganisms that covers the entire land and is visible to us is known as soil. All living creatures including plants, animals as well as microorganisms grow and dwell on this layer of the earth’s crust. This soil is composed of around \(45\% \) minerals, \(5\% \) organic matter, \(25\% \) water, and \(25\% \) air. Let us learn about Soil Profile in this article below.

To simplify the study of soil, they are divided into vertical layers of the soil which shows all other layers of the soil that is known as the soil profile. Just like our Facebook profile tells us all about us, similarly, soil profile tells all about the soil! Each layer of the soil profile is divided into different horizons with different physical properties. The various horizons of soil are \({\rm{O}}\) horizon (organic layer), \({\rm{A}}\) horizon (Topsoil), \({\rm{B}}\) horizon (Subsoil) and \({\rm{C}}\) horizon (Parent material), \({\rm{R}}\) horizon (bedrock). In this article, let’s learn everything about soil profiles in detail.

What is Soil Profile?

The vertical section of the soil from the top surface to the bottom layer where the soil meets the underlying rocks is defined as a soil profile. The various layers can be easily identified by the soil’s colour and particle size.

With the help of the study of soil horizons, one can understand the hydrologic processes within the soil and this provides evidence of the movement of water in a particular direction as well as its magnitude.

Explain Soil Profile

The soil profile is a very important tool in nutrient management as by scrutinizing a soil profile, we can gain valuable perceptions of soil fertility. Due to weathering of rocks and decomposition of organic matter, the profile of the soil changes from place to place.

For example, a highly weathered, infertile soil is mostly a light-coloured layer in the surface of the soil from which nutrients are leached away. Conversely, a highly fertile soil often has a deep coloured surface layer and contains high amounts of organic matter. With the help of these clues provided by soil profile, we can predict how soil will perform under certain nutrient management conditions as well as their uses.

Different layers of soil are broadly classified as:

1. Topsoil
2. Subsoil
3. Parent rock
4. Bedrock

Each layer of the soil has its well-defined role in nature. Various soil samples differ in their texture, structure, colour, and many other factors which are very important to determine soil usage. It takes several years for soil to develop these simplest three layers (Topsoil, Subsoil and Parent rock).

Soil Profile Diagram with Explanation

What are the Types of Soil Profile?

A soil horizon is a distinct layer parallel to the soil surface that differs in various physical, chemical, and biological characteristics of the soil. The soil profile expands from the soil surface to the parent rock material.

Four major components of soil include:

1. Inorganic minerals
2. Organic matter
3. Water and air
4. Living matter (microorganisms)

Horizons of Soil

Based on the physical, chemical, and biological properties, the soil is classified into various horizons represented by the letters: \({\rm{O,}}\,{\rm{A,}}\,{\rm{E,}}\,{\rm{B,}}\,{\rm{C}}\) and \({\rm{R}}\) which are as follows:

The O-horizon

This is the topmost layer of the soil surface that is composed of organic materials such as dried leaves, twigs, grasses, dead animals, etc., that are decomposed. This horizon is more prominent in forest areas where the debris that falls from trees gets accumulated. The soil of this layer has dark brown or black colour.

The A-horizon

This is a surface horizon also known as the topsoil, consisting of minerals (sand, silt, and clay) and considerable amounts of organic matter such as humus. In this horizon, seed germination takes place and is predominantly the fertile surface layer of many soils in grasslands and agricultural lands. This layer is rich in several microorganisms such as bacteria, fungi, earthworms, etc.

The E-horizon

This is a subsurface horizon beneath the \({\rm{O}}\) and \({\rm{A}}\) horizon that has been heavily leached (eluviation). Leaching is the process in which soluble nutrients such as silicate, clay, iron, etc., are lost or extracted from the soil due to precipitation or irrigation having a concentrated amount of sand and silt particles. This horizon is mainly light in colour.

The B-horizon

This is a subsurface horizon also known as subsoil that has accumulated from the above layers of the soil and is comparatively more compact and harder than the topsoil. It contains less amount of humus, soluble minerals, and organic matter and is a site of deposition of certain minerals and metal salts. Due to the presence of clay, this layer holds more water than the topsoil.

The C-horizon

This horizon is above the bedrock known as parent rock and mainly consists of weathered and partially decomposed rock. This layer is known as parent material because the upper layers are formed from this layer only.

The R-horizon

This is the lowest layer consisting of a mass of rock such as granite, basalt, limestone or sandstone, quartz and is known as bedrock.

Importance of Soil Profile

1. One of the most important concepts in soil science is the soil profile. It is a key concept to understand the entire processes that have during soil development.
2. The soil profile is the means of determining the various types of soil that help the farmers to understand the type of crops to be grown in a particular area.
3. A deep study of the soil profile is important from crop husbandry since it discloses the surface and the subsurface characteristics and qualities of soil such as depth, texture, structure, drainage conditions of soil, and soil-moisture relationships, which directly affect the growth of the plants.
4. The soil profile plays a very important role in nutrient management as it helps in gaining valuable perceptions of soil fertility.
5. We get pure groundwater due to this soil profile only. Rainwater penetrates deep inside the soil and gets collected which also increases the water table of the earth.

Summary

In a nutshell, we can say that soil is the foundation of all life on the earth. Without soil, plants cannot grow and thus we cannot get food from them to live. Soil is the surface covering the earth’s crust and as such has five layers named organic matter, topsoil, subsoil, parent rock, and bedrock. Soil contains lots of organic matter, inorganic matter, water, and air. A handful of soil may contain billions of bacteria and other microorganisms.

Soil is made up of many layers known as horizons. They are \({\rm{O}}\) horizon (organic layer), \({\rm{A}}\) horizon (Topsoil), \({\rm{B}}\) horizon (Subsoil) and \({\rm{C}}\) horizon (Parent material), and \({\rm{R}}\) horizon (bedrock). Each layer has characteristics that make it different from the other layers.

We all stand and live on \({\rm{O}}\)-horizon which is the topmost layer. A horizon or Topsoil is composed of humus, it is porous and holds enough water and air. This is the reason that seeds germinate in this layer of soil and the roots of the plants grow. Just below the topsoil lies the subsoil or \({\rm{B}}\) horizon. It is comparatively tighter and harder than topsoil. This layer is rich in minerals and metal salts. \({\rm{C}}\) horizon or Parent material consists of large rocks and the bottom-most layer is bedrock situated several feet below the surface. All the layers of soil are very important in some or the other way.

FAQs

Q.1. What is the soil profile?
Ans: The vertical layers of the soil show all other layers of the soil that is known as the soil profile. Each layer of the soil profile is divided into different horizons with different properties. The various horizons of soil are \({\rm{O}}\) horizon (organic layer), \({\rm{A}}\) horizon (Topsoil), \({\rm{B}}\) horizon (Subsoil) and \({\rm{C}}\) horizon (Parent material), and \({\rm{R}}\) horizon (bedrock).

Q.2. What determines the thickness of the soil profile?
Ans: The thickness of the soil profile varies from place to place due to weathering, humus formation, and soil accumulation.

Q.3. How to draw soil profile?
Ans:

Q.4. Which three layers form the soil profile?
Ans: The simplest soil profile consists of three layers: Topsoil ( \({\rm{A}}\)-horizon), Subsoil (\({\rm{B}}\)-horizon), and the inner layers (\({\rm{C}}\)- horizon).

Q.5. Which horizon of soil profile contains a lot of humus?
Ans: The \({\rm{A}}\)- horizon, also known as the topsoil of the soil profile, contains a lot of humus. Due to this reason, this layer is dark in colour.

We hope this detailed article on Soil Profile helps you in your preparation. If you get stuck do let us know in the comments section below and we will get back to you at the earliest.