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Soil Formation

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The soil is considered to be one of the most essential natural resources and is the base for the growth of vegetation, on which our nutrition and livelihood depend upon. Soil is also the main source on which many microorganisms such as earthworms, rates, and also several other species live upon.

What is Soil?

Soil refers to the uppermost layer of the surface of the Earth and is formed by the processes of weathering of mountains over thousands of years. The main components soil is made of include minerals, organic materials, water, and air. The essential components on which the texture of soil depends include sand, silt, and clay. Leaves as well as organic constituents help in decomposing the upper organic layer, known as the humus and the humus plays a very significant role in fertility.

Soil Formation

Soil formation takes place through a plethora of processes, which include weathering of rocks and mixing of rock materials with organic debris which is formulated by the decay of plants; other processes is a slow chemical alteration of water that seeps through the weathered rock materials after rains.

Weathering is the process by which rocks are broken down to form smaller particles which ultimately leads to soil formation that includes both geological sediments and organic debris. It takes around 500 years for the formation of 1 cm of soil from harder rocks. Combined processes of physical, chemical, and biological factors including weathering of rocks, under environmental conditions, lead to soil formation; a mixture of biotic and abiotic components; all of which make the soil fertile which is suitable for the growth of plants or agriculture.

Soil Formation Diagram

Soil Formation Diagram

Soil Formation Diagram

Factors of Soil Formation

The soil formation depends on the processes which are listed below:

Parent material

Few soils weather directly from underlying rocks. These “residual” soils have the same general chemistry as the original rocks. The material in which soil forms is called parent material. The parent material is mostly weathered by chemical and physical processes and transported, which is then deposited to form layers of soil. Bedrock is usually the parent material, but soil also gets transported because of factors like wind and water.

Organisms

Organisms include plants, animals, microorganisms, and fungi. They play a vital role in the formation of soil and are important determinants of the impact on the physical and chemical environments of the soil.

Climate

Soil formation prefers heat and moisture. In case, the climate is dry and cool, the rate of soil formation decreases. The prevailing climatic conditions determine the nature of weathering process, the place, and rates of both physical and chemical processes. Climate affects the kind of vegetation in an area, which affects the process of soil formation.

Topography

Topography refers to the configuration of the surface of the land and the relation of land with man-made and also natural features. The shape of the land and also the position of the slope on the landscape are important parts of topography.

Time

The time taken for the soil formation affects the quality of the soil. Soil formation tends to take place over thousands of years by undergoing significant changes and eventual formation. Soils within certain age brackets are young and tend to have weak soil horizon development.

Factors for Soil Formation

Factors for Soil Formation

Factors for Soil Formation

Soil Formation Process: Weathering Agents

The important carriers or the weathering agents of soil formation are as mentioned below:

Glacier

When the glaciers tend to move from one part to another, the soil is pushed further with them and the drifted materials are deposited miles away from the place of its formation and when the glaciers tend to melt, huge heaps of soil are left and part of that soil is carried by the streams.

Water

The soil particles are transported with water, as the rivers flow. The smallest particles of the soil are transported further and heavier particles are settled down earlier soils are deposited along banks of rivers, termed to be alluvial soil, which is rich in mineral contents and rainfall also tends to play a very important role.

Wind

Wind plays a vital role in the transportation of huge quantities of soil from one place to another and loose soils are carried away by the wind from one place to the next.

Soil Formation and Weathering Processes

The following are important weathering processes on which soil formation depends:

Freezing and Melting

A process of continuous freezing and melting, results in the formation of cracks in the rocks, and the presence of the sun expands the surface of the rock. Coming in contact with water bodies, these pores are filled with water and the water tends to be expanded when frozen, which kind of pushes the particles apart and breaks them. With the melting of ice, rocks are broken into loose particles of soil.

Heating and Cooling

In places of extreme climatic conditions, like arctic or arid regions, the rocks tend to be subjected to sudden expansion as well as contraction, which results in the loosening of the particles, and air content increases. Over time, rocks are reduced to loose soil with significant effects working on it.

Wetting and Drying

The rocks tend to shrink when dry and expand/swell when they are wet. Daily wetting as well as drying of rocks results in the process of loosening the grains.

Grinding or Rubbing

At the time of waves, the rocks are pounded along the seashore, and the processes of abrasion of the upper layer occur with fragmentation into smaller rocks and which further break into smaller particles.

Organisms

Organisms play a very vital role in churning way through the soil and by eating it. This results in the formation of nutrient-rich manure in form of their excreta and their movements help in the mixing and aeration of the given soil.

Soil Profile

 It is a vertical cross-section of soil, made of layers parallel to the surface. Each layer of soil has a different texture and is called a horizon.

  1. Horizon A (Topsoil): It is the topmost layer where organic materials are engulfed with mineral matter, nutrients, and water; essential elements for the growth of plants.
  2. Horizon B (Subsoil): This zone has a greater content of minerals and humus is present in lesser quantities. Contains materials from both above and below layers.
  3. Horizon C ( weathered and decomposed rock): Comprises loose parent rock materials and is the first stage of soil formation.

Soil Profile Diagram

Soil Profile

Soil Formation Diagram

Classification of Soils

Based on the factors responsible for soil formation, color, thickness, texture, age, and chemical and physical properties, The soil is classified as:

  1. Alluvial Soil
  2. Black Cotton Soil
  3. Red & Yellow Soil
  4. Laterite Soil
  5. Mountainous or Forest Soil
  6. Arid or Desert Soil
  7. Saline and Alkaline Soil.
  8. Peaty and Marshy

Alluvial Soil

The major part of India under Alluvial soil is Northern India and its river valley – the Ganga, the Indus, and the Brahmaputra.

The composition of alluvial soil is sand, silt, and clay. Soil particles appear to be bigger as we move inner toward river valleys whereas the soils are coarse, on the upper side of the river valley. They are rich in potassium but lack phosphorus present.

Based on age Alluvial soil is classified into two categories:

  1. Bhangar (Old Alluvial): This soil contains a higher concentration of Kankar or stones than the Khadar.
  2. Khadar (New Alluvial): This kind contains fine particles therefore it is more fertile than the Bhangar.

These soils contain an adequate proportion of minerals such as Phosphorus, potash, lime, etc. needed for the growth of sugarcane, paddy, wheat, and other cereal and pulse crops.

Black Soil

Black soil is also known as “Regur soil”. It covers most of the Deccan Plateau – Madhya Pradesh, Gujarat, Andhra Pradesh, parts of Maharashtra,  and some parts of Tamil Nadu. This soil is ideal for the growth of cotton that’s why this soil is also called Black cotton soil.

The black consists of extremely fine particles of clay and has a very good tendency to hold moisture. Black soil is full of nutrients suited for plant growth and contains calcium carbonate, magnesium, potassium, and lime also.

Mainly cultivated plants in Black soil are Cotton, pulses, millets, castor, sugarcane, citrus fruits, linseed, etc.

Red and Yellow soil

This type of soil develops in areas of low rainfall on the crystalline igneous rocks in the southern and eastern parts of the Deccan plateau.

Due to the diffusion of iron in crystalline and metamorphic rocks, this soil develops a reddish color. When it is under-hydrated form the color appears yellow.

The region in India is found in parts of Chhattisgarh, Odisha, southern parts of the middle Ganga plain, and some parts of western ghats. Crops grown in this soil are wheat, cotton, oilseeds, tobacco, and pulses.

Laterite Soil

The part of India under laterite soil is, in the Karnataka, Kerala, Tamil Nadu Western Ghats region of Maharashtra, Odisha, some parts of West Bengal, and north-eastern states also. The laterite soils are generally acidic having ph less than 6.0 which doesn’t have enough nutrients for plants. Although low fertility, they respond to manures and fertilizers.

Under tropical and subtropical climates with alternate wet and dry seasons, laterite soil develops. The soil supports evergreen and deciduous forests but humus concentration is poor. For tea and coffee plantations this soil is favorable. Red laterite soil in Kerala, Tamil Nadu, and Andhra Pradesh for tree crop cultivation like cashew nuts. Laterite soil hardens rapidly and is hence used as bricks.

Arid Soils

The color of Arid soil is Reddish brown. This soil is generally saline in nature and sandy in texture. This kind of soil has lack humus and moisture content. This type of soil has a high saline level. This soil is found abundantly in Rajasthan and contains less humus and organic matter.

Because of the increasing calcium content downwards, the lower horizons of the soil are occupied by Kankar. The Kankar layer formations in the bottom horizons lead to the filtration of water.

Forest Soils

This soil is found in forest regions where rainfall is sufficient. These soils are coarse-grained in the upper slopes and loamy and silty valley sides. It is found in the northern region of India such as Punjab, Uttar Pradesh, Bihar, West Bengal, and Assam. The soil texture is coarse-grained on the upper slopes and loamy and silty on the valley sides. The soil is fertile in the river valleys.

Peaty and Marshy Soils

This soil is found in heavy rainfall and high humidity supports good vegetation. This soil is rich in humus and organic matter. This soil is heavy and mostly black.

Mostly this type of soil is found in southern Uttarakhand, the northern part of Bihar, and coastal areas of West Bengal, Odisha, and Tamil Nadu.

Also, Read

FAQs on Soil Formation

Q1: How is soil formed?

Answer:

Soil is formed by breaking down of the rocks at or near the surface of Earth through the processes like physical, chemical, and biological processes by various factors like that of sun, water, wind, and living organisms.

Q 2: What are the factors of soil formation?

Answer:

The factors of soil formation include the parent material, climate, biota, topography, and also time.

Q 3: What are the soil formation processes?

Answer:

The soil formation processes include weathering and natural erosion. Some important factors include water, wind, temperature change, gravity, chemical interactions, organisms, and pressure differences.

Q 4: What is the composition of the soil?

Answer:

The composition of the soil is minerals, organic matter, water, and also soil.

Q 5: What is the ideal pH for soil?

Answer:

The ideal pH of the soil lies normally between 6.0 ad 7.0 and most soils have a pH scale value ranging from 3.5 and 10.


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Last Updated : 03 Apr, 2023
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