Soil: Composition, Importance & Formation

Soil is the loose surface material that covers most of the land. It is a source of nutrients and water for the plants and also provides agricultural support to them. Soil is made up of both organic and inorganic particles and varies widely in terms of its physical and chemical properties. The nature of the soil is affected by different factors such as temperature, precipitation, etc. The gradual removal of the top layer of the soil due to natural factors is known as soil erosion.

Key Terms: Soil, Living Organisms, Organic Matter, Minerals, Types of Soil, Soil Profile

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What is Soil?

Soil is a mixture of minerals, living organisms, and organic matter. It is referred to as any loose sediment of land. Technically, the soil is made up of 45% minerals, 5% organic matter, and 50% voids or empty spaces. Many types of soil are found all over the world and these are classified as - 

• Clay Soil
• Loamy Soil
• Silt Soil
• Sandy Soil

A soil can perform many important functions such as - 

• It provides a medium for the growth of plants.
• It provides habitat to many organisms.
• It acts as a modifier of the atmosphere of the earth.
• It is one of the most important components of the biosphere.

Some of the important properties of the soil are texture, absorption of water, moisture, color, pH of the soil, and percolation rate.

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Soil Profile

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During its formation, the soil is arranged in the form of layers known as horizons. The layers of soil can be easily distinguished by the color of the soil and the size of the particles. The main layers of the soil are topsoil, subsoil, and the parent rock. These layers of soil profile are - 

1. Horizon A or Topsoil

The topsoil is rich in organic material and is known as the humus layer.

• This layer is made up of decomposed organic matter.
• Therefore, the topsoil has a dark brown color.
• Seeds germinate and roots grow in this part of the soil.

2. Horizon B or Subsoil

A hard and compact layer below the topsoil is known as the subsoil.

• It has a light color as it has less humus content.
• This layer of the soil contains metal salts, especially iron oxide.

3. Bedrock or Horizon C

The parent rock below the subsoil is known as the bedrock.

• It has no organic matter and is formed of rocks and stones, therefore it is very hard.
• This Horizon C layer is a transition layer between the bedrock of the earth and horizon A and B.

Read More: Natural Resources Management

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Composition of Soil

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Soil is a heterogeneous mixture. It is made up of organic matter, different gases, minerals, and water. The composition of the soil is as explained below - 

Organic Matter

Organic matter is mainly composed of animals and plants. It is found in really small amounts in the soil. Organic matter can be further classified into three types depending on the stages of the decomposition- 

• Undecomposed organic matter
• Partially decomposed organic matter
• Completely decomposed organic matter

Gaseous Components

The pores of the soil filled with the soil have gaseous components. These pores are generally filled with oxygen and nitrogen.

• The gaseous components include the atmospheric air which is fixed by the microorganisms.
• However, due to the gas that is produced by the microorganisms that are in the soil, the composition of carbon dioxide is higher in the soil

Minerals

Minerals are an essential element of the composition of the soil. 

• Minerals are solid components that are made of atoms. 
• They naturally occur and have a fixed chemical composition in the soil. 
• The main minerals present in the soil are feldspar and olivine.

Water

The nutrients and the minerals are dissolved in the soil and then transported to the different parts of the plants. Water is needed for the development and growth of plants.

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Importance of Soil

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Soil is an important element that is necessary for the survival of living organisms. The importance of soil is as given below:

• Soil is used to form tiles, cups, and utensils. 
• The fertile soil helps in the development and growth of the plants. Therefore, the plants that are produced are healthy and thus they provide furniture, food, medicines, and clothing.
• The contents of the soil such as sand, clay, and gravel are used to construct homes, buildings, and roads.
• The topsoil supports some life activities such as hatching, reproduction, breeding, and nesting of a few microorganisms.
• The soil also absorbs the rainwater. The water is then evaporated and released into the air on sunny days which contributes to making the atmosphere cool.
• It supports multiple life forms such as algae, bacteria, and fungi which maintain environmental balance. They decay the dead organisms and retain the moisture.
• Certain mineral medicines are extracted from the soil for cosmetics. Some of them include iron, calcium, and other substances like petroleum jelly.
• Soil also has many elements and minerals that are needed for the plants to carry out different cellular activities.

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Types of Soil

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The different types of soil can be classified as - 

1. Sandy Soil

This soil is less fertile and is highly porous. Due to bigger particles, it has more air space. 

2. Clayey Soil

This soil has small air pockets and very fine particles. Due to the presence of humus and minerals, this soil is more fertile.

3. Loamy Soil

This soil has a high humus content and an adequate amount of porosity for the healthy growth of the plants. Loamy Soil has more air space than clayey soil but less than sandy soil.

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Things to Remember

• Soil is a loose surface covering that is made up of organic matter, gaseous components, minerals, and water.
• The different layers or horizons of soil are known as topsoil, subsoil, and bedrock.
• As per their properties, soil can be classified as sandy, clayey, and loamy soil.
• A soil provides habitat to multiple organisms.
• It is an important component of the biosphere that provides a medium of growth to the plants.