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How is Soil Formed: process and role of soil for plant growth

Dr Ahsanur Rahman, PHD

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How is Soil Formed
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Soil is one of the most important natural resources on Earth. It is the thin layer of material that covers the planet’s surface and is vital for the growth of all plants. Soil is formed by a process of weathering and erosion. Weathering is the process by which rocks and minerals are broken down into smaller pieces by the action of wind, water, and ice. Erosion is the process by which these smaller pieces of rock and mineral are moved and deposited by wind, water, and ice. Over time, this process of weathering and erosion creates a thin layer of soil on the Earth’s surface.

“The soil is that thin layer of the earth’s surface which supports few of the terrestrial and aquatic plants and hence, many animals”

Factors Affecting Soil Formation

Factors affecting soil formation include climate, organisms, topography, parent material, and time. These factors interact and influence each other to shape the characteristics and properties of soil.


Climate plays a significant role in soil formation. Temperature and precipitation patterns determine the rate of weathering and the types of weathering processes that occur. For example, in cold climates, freeze-thaw cycles can cause rocks to fragment and contribute to soil particle formation. In contrast, in tropical climates, high temperatures and frequent rainfall promote intense chemical weathering, which leads to the breakdown of minerals and the release of nutrients into the soil.


Organisms, such as plants, animals, and microorganisms, are essential in soil formation. Plant roots penetrate the soil, physically breaking it apart and creating spaces for air and water movement. As plants grow and die, they contribute organic matter to the soil, enriching its fertility. Soil microorganisms, including bacteria and fungi, play a crucial role in decomposing organic materials and releasing nutrients. Animals, such as earthworms, burrow through the soil, improving its structure and aiding in the mixing of materials.


Topography refers to the shape and slope of the land. Slopes affect the flow of water, which can lead to erosion or waterlogging. Erosion removes valuable topsoil, while waterlogging can affect soil aeration and nutrient availability. The aspect, or direction a slope faces, also influences soil formation by affecting the amount of sunlight and temperature different parts of the soil receive.

Parent material refers to the underlying rocks or sediments from which soil is derived. Different parent materials have varying mineral compositions, which influence the fertility and characteristics of the resulting soil. For example, soils derived from limestone parent material tend to be more alkaline, while soils derived from granite parent material are usually more acidic.


Time is a crucial factor in soil formation. It takes thousands or even millions of years for soil to develop. Over time, weathering processes, the accumulation of organic matter, and the action of organisms transform parent material into soil. The length of time soil has been forming also affects its fertility and maturity. Older soils tend to have more developed soil horizons, structure, and nutrient profiles.

Human activities

Human activities can accelerate or alter soil formation processes. Agricultural practices, deforestation, construction, and pollution can all impact soil formation. For example, intensive farming practices can deplete soil nutrients and degrade soil structure. Soil erosion caused by deforestation and improper land management can lead to the loss of topsoil and make the land unsuitable for cultivation.

Understanding the factors affecting soil formation is vital in various fields. In agriculture, it helps farmers make informed decisions about soil management practices, such as irrigation, fertilization, and erosion control. Environmental scientists and land managers rely on this knowledge to assess soil quality and develop sustainable land use strategies. By considering these factors, we can better appreciate the intricate processes that contribute to the formation and maintenance of this valuable natural resource.

Major Factors of Soil Formation

Soil formation is a complex process that involves the interplay of several factors, each playing a significant role in shaping the characteristics and properties of the soil. Understanding these major factors is crucial in comprehending how soil is formed and how its fertility and suitability for plant growth is determined.

1. Parent Material: The parent material is the initial foundation upon which soil formation begins. It refers to the pre-existing rock or sediment that is weathered and broken down into smaller particles. The type of parent material greatly influences the properties of the resulting soil, such as texture, mineral composition, and nutrient content. Different types of parent material, such as igneous rocks, sedimentary rocks, or organic materials, can lead to the development of soils with distinct characteristics.

2. Climate: Climate plays a vital role in soil formation. It encompasses temperature, precipitation, and wind patterns. These climatic conditions influence the rate and intensity of weathering processes that break down the parent material, such as physical weathering (e.g., freeze-thaw cycles) and chemical weathering (e.g., exposure to acidic rainwater). The amount and frequency of rainfall affect the leaching and transportation of nutrients and minerals within the soil, and temperature regulates the rate of biological activity in the soil.

3. Topography: The physical features of the land, known as topography, have a significant impact on soil formation. Slopes, elevation, and drainage patterns affect the movement of water and materials across the land. Steep slopes can lead to rapid erosion, which can result in the loss of valuable topsoil layers. Furthermore, the accumulation of water in poorly drained areas can cause waterlogging, affecting the composition and characteristics of the soil.

4. Biological Activity: Biological components, including plants, animals, and microorganisms, are vital contributors to soil formation. Plant roots penetrate the soil, creating pore spaces and promoting the formation of soil structure. As plants grow and eventually die, they contribute organic matter to the soil through decaying plant material and root exudates. Microorganisms play a crucial role in decomposing organic materials, releasing essential nutrients, and facilitating the breakdown of complex organic compounds.

5. Time: Time is an essential factor in soil formation. Soil development is a slow and continuous process that occurs over extended periods, typically measured in centuries or even millennia. With time, the accumulation and transformation of organic matter, the weathering of parent material, and the interactions among the various factors gradually shape the soil’s properties. The longer the soil has been developing, the more mature and well-developed it becomes, with better-defined soil horizons and increased fertility.

Understanding these major factors of soil formation provides valuable insight into the intricate processes that give rise to the diverse range of soils found across the globe. By considering the parent material, climate, topography, biological activity, and the passage of time, scientists can better predict and manage soil quality, fertility, and sustainability. Recognizing the importance of these factors is essential for promoting sustainable agriculture, ensuring the availability of fertile soils, and preserving this precious natural resource for future generations.

Parent Material and Its Role in Soil Formation

One of the major factors influencing soil formation is the parent material. The parent material refers to the pre-existing rock or sediment from which soil is formed. It plays a crucial role in shaping the characteristics and properties of the soil.

Parent Material: The initial foundation of soil formation, is influenced by the type of rocks or sediments.

Climate: Temperature, precipitation, and wind patterns affecting weathering processes and nutrient leaching.

Topography: Physical land features impacting water movement and erosion.

Biological Activity: Plants, animals, and microorganisms contribute to soil structure and nutrient cycling.

Time: Soil development occurs gradually over centuries, influencing soil maturity and fertility. Understanding these factors helps predict and manage soil quality, promote sustainable agriculture, and preserve this vital resource for the future.

Sedimentary Rocks

  • formed by the accumulation and compression of sediments over time.
  • Provide insights into Earth’s history and past environmental conditions.
  • Types include sandstone, limestone, and shale, each with unique characteristics.
  • Play a critical role as natural reservoirs for resources like oil and gas.

Volcanic Rocks

  • Formed from magma cooling on the Earth’s surface after volcanic eruptions.
  • Basalt is common and used in construction; pumice is lightweight and used in horticulture.
  • Obsidian has a glassy texture and is popular for jewelry and decoration.
  • Valuable for understanding Earth’s history, predicting eruptions, and resource exploration.

Igneous Rocks

  • Originates from solidification of molten magma.
  • Classified as intrusive (slow cooling) or extrusive (rapid cooling).
  • Examples include granite, basalt, and pumice, with diverse compositions and uses.
  • Offers insights into geological history and resource distribution.

Metamorphic Rocks

  • Formed from pre-existing rocks undergoing changes due to heat, pressure, and chemical activity.
  • Types include marble and quartzite, with distinct textures and uses.
  • Provide valuable information about Earth’s geological processes and history.
  • Valued in construction and design industries for their durability and appearance.

Weathering Processes in Soil Formation

Weathering is essential for soil formation, involving the breakdown of rocks and minerals into smaller particles. Physical weathering includes freeze-thaw and abrasion, while chemical weathering involves reactions altering rocks. Both contribute to soil particles, releasing minerals and organic matter. This fertile topsoil supports plant growth. Climate, parent material, and organisms influence weathering rate. Understanding weathering is vital for agriculture, land management, and ecosystem health.

Physical Weathering

Physical weathering is a vital natural process in soil formation. Unlike chemical weathering, it breaks rocks physically without altering their chemical composition. Freeze-thaw weathering and abrasion are common processes that contribute to soil particle formation. Human activities can also impact physical weathering. Understanding this process is essential in geology, agriculture, and construction, as it increases surface area for chemical weathering, aids soil formation, and influences landscape history, soil structure, and structural stability.

how soil is formed

The Different Types of Soil

There are many different types of soil, each with its own characteristics. The most common types are clay, sand, loam, and silt.

Clay soil is made up of very small particles that pack together tightly. This type of soil is often difficult to work with because it can be hard to dig through and is easily compacted. Clay soil is also known for being very fertile, meaning it is great for growing plants.

Sand soil is made up of larger particles than clay soil. This type of soil is easy to work with and is often used in gardening. Sand soil is not as fertile as clay soil, but it can still support plant growth.

Loam soil is a mix of sand, clay, and organic matter. This type of soil is easy to work with and is very fertile, making it ideal for growing plants.

Silt soil is made up of very fine particles. This type of soil is easy to work with and is very fertile, making it ideal for growing plants. However, silt soil can easily be compacted, so it is important to take care when working with it.

The Importance of Soil Formation

Soil is one of the most important components of Earth’s natural environment. It provides essential nutrients for plants, animals, and microorganisms to live and thrive. It also acts as a filter for water and air, helps to moderate temperatures, and serves as an anchor for plants. Soil formation is a complex process that involves several chemical, physical, and biological processes that occur over long periods of time .

Soil formation begins with the weathering of rocks and minerals into smaller particles known as regolith. Weathering occurs through physical processes such as abrasion, or through chemical processes such as oxidation and hydration. Once these particles are created they are transported by water, wind, or ice to form new soil deposits. The soil is then modified further by living organisms, which introduce organic matter, such as plant roots and other decaying material. This organic matter helps to improve the quality of the soil by increasing its fertility and water-holding capacity.

Soil formation is a continuous cycle that is affected by climate, topography, biota, and time. Climate determines how quickly weathering occurs and the rate of soil formation. Topography affects the amount of runoff and erosion and also plays an important role in shaping the soil profile. Biota, such as plants and animals, also influence soil formation by providing organic matter. Finally, time is a major factor in soil formation because of the long period of time it takes for weathering and other processes to occur.


Soil is an important part of the environment that sustains life on Earth. It is a complex mixture of minerals, organic matter, gases, liquids, and countless organisms that interact to support plant life. The formation of soil is a slow process that can be impacted by a variety of human activities. deforestation, for example, can lead to erosion and the loss of valuable topsoil. careless farming practices can also degrade the quality of soil, diminishing its ability to support plant life and ultimately impacting the food supply for the entire human race.