Formation of Soil | Soil Profile, 3 Horizons, Process & Factors

Formation of Soil

Formation of soil is done by the weathering of rocks and soil is the thin layer of material covering the earth’s surface and is made up mainly of organic materials, mineral particles, air, water, and living organisms.

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Soil is the main source of food for humans, animals, and birds and most plants get their nutrients from the soil. So, for existence, most living things on land depend on soil, and the soil is a valuable resource that needs to be carefully managed.

The Soil Profile:

By parallel layers or horizons of different soil and rock materials, a soil profile is made up and as two main layers such as topsoil and subsoil, most soil profiles cover the earth.

soil profile

The soil profile is quite a complex process and develops over a long period of time.

The major points in the soil profile are;

  1. There are following factors interact to form the soil profile which includes climate, vegetation cover, parent rock material, and topography.
  2. By weathering or deposition processes, soil profiles may be formed, and to form part of the soil profile, parent material sitting on top of bedrock may be weathered.
  3. The rain from duplex soil types and by wind, the addition of organic matter on the surface, or deposits are carried.
  4. To create the B horizon, fine clays and mineral salts wash down through the topsoil, and to form hardpans in the profile, fine particles can cement together in cultivated soil.
  5. Soil biota breaks down organic matter and in the soil, it forms pores and clusters.

The depth of the topsoil varies due to factors like climate, vegetation cover over time, and erosion.

Horizons of Soil:

As you move down the soil profile soil horizons are the layers in the soil and a soil profile may have soil horizons.

There are three main horizons of soil as given below;

  1. A-Horizon or Topsoil
  2. B-Horizon or Subsoil
  3. C-Horizon or Bedrock

A-Horizon or Topsoil:

This horizon is rich in organic material and also called the humus layer. The topsoil layer consists of organic matter and decomposed material that’s why the color of topsoil is dark brown. To hold enough air and water, the hummus makes the topsoil soft and porous and in this layer of soil, many living organisms like earthworms, millipedes, and centipedes, bacteria, and fungi are found.

B-Horizon or Subsoil:

This horizon is just below the topsoil and as compared to the topsoil layer it is comparatively harder and compact. There is less humus in this layer and due to this, it is lighter in color than the topsoil. This layer is rich in minerals brought down from the topsoil but less organic and it contains especially iron oxide in a large proportion and metal salts. When farmers plow their fields they often mix A-horizon and B-horizon.

C-Horizon or Bedrock:

Bedrock lies just below the subsoil and also known as parent rock. This layer is very hard because it is made up of stones and rocks and contains no organic matter. Between the earth’s bedrock and horizon A and B, this layer represents a transition zone.

soil horizons

Process of Formation of Soil:

The soil has taken thousands of years to form and in the following ways the formation of soil take place;

  1. By continuous action of wind and rain, big rocks break down into smaller rocks and to break down into smaller rocks it takes many years for these rocks.
  2. By two types of weathering such as physical weathering and chemical weathering, rocks are mainly broken and to form tiny particles of soil, a number of natural force (called agents) works to break down the parent rock and these agents include water, wind, the sun’s heat, and animals and plants.
  3. To form sand and silt and ultimately into finer particles, these pieces get further broken down. The process is very slow and to form a just 1cm layer of soil it takes thousands of years. The top layer of the soil is formed by these fine particles.

Factors of Formation of Soil:

There are the following factors affecting the formation of soil as given below;

Parent Material:

The most important factor in the formation of soil is parent material. The parent material refers to the mineral material or organic material from which the soil is formed and these soils will carry the characteristics of its parent material like texture, color, structure, and mineral composition. For example, the soil will be red in color and have the same feel as its parent material if soils are formed from an area with large rocks of red sandstone.


To form soil can take many years and younger soils have some characteristics from their parent material. The addition of organic matter, exposure to moisture, and other environmental factors may change its features as they age and they settle and are buried deeper below the surface with time. it is an important factor in the formation of soil.


This is also the most important factor in the formation of soil and two important climatic components such as temperature and precipitation are important. They determine what kind of organic materials may be available on and inside of the soils and how quickly weathering will be.

A warmer climate with more rainfall means more animal action and more vegetative cover and it also means more water erosion, more percolation, and more runoff. To determine the kind of soils in an area, they all help in it.


By organisms such as plants, the formation of soil is influenced, and plants are grown in the soil. The plants mature, die and new ones take their place in soils and to the soil, their leaves and roots are added and animals eat plants and their wastes, and eventually, their bodies are added to it. It is also an important factor in the formation of soil.


This factor of formation of the soil refers to the landscape position and the slopes and long slops potentially erode the surfaces of slopes because water will run down faster. The effect will be richer deposits at the foot of the slopes and poor soils on the slopes and slopes may also be exposed to more direct sunlight which may dry out soil moisture.


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