Soil Formation

The soil is come from rock initially. This is termed the parent material. This parent material may be directly below the soil and a great distance away if wind, water and Glacier have transported the soil.

Soil Formation

Formation of soil is termed as pedogenesis. Soil formation is dependent upon the other prevailing process which affecting the soil formation. Soils are formed by the interaction of different soil forming factors and processes.

Soil Formation

In India, about four hundred soil series have been recognized and many more are being introduced as soil survey and mapping is extended to other areas.

Soil formation is a process of two different phases :-

1. Weathering of rocks and minerals and decomposition of rocks and minerals. (destructive phase of soil formation)

2. The development or the formation of soil by some soil forming factors and pedogenic processes. (constructive phase of soil formation)

The first phase of soil formation i.e. weathering of rocks and minerals is considered as the destructive phase and help to change the consolidated rocks and minerals into unconsolidated minerals (parent material) whereas the second phase of soil formation is considered as the constructive process and developed the soil profile.

Climatic condition play an important role behind the soil formation :-

The soil formation can be seen as the combination of different products of weathering of structural growth of the soil. The structure is differentiate as horizon or layers and at last it is moved or translocate to the new place.

Water play a very important role in moving the soil particles like a river flow and then they transport the particle of soil along with.

The heavier particle of the soil such as sand will be dropped earlier by the river while a small particle will be carried the furthest by the river flow as they weigh the least. So from this, the different type of clay or sand is soil formed. Texture of soil depends upon this.

The soil which is deposit around the lake or river is called Alluvial soil and the soil which is deposited near the lake is called lacustrine.

Rainfall is also an important part in washing soil off from the land. The small force of rain drop can also move the soil particles.

If this process happen around the field the process is called sheet erosion and from this erosion, the soil particles of soil translocated to the other place and then it forms another type of soil in other place.

The wind is also important to move the soil particle in a large quantity on occasions, fine soil deposits can be seen in many regions near the desert or ocean.

Factors of soil formation

S = f{cl, o, r, p, t,…}

S = Soil formation,

cl = climate,

o = organisms,

r = topography,

p = parent material and

t = time.

Climate :- Includes temperature, rainfall, humidity and wind. Rainfall and temperature are most important factors.Soil properties affected by climatic conditions are pH, base saturation of exchange complex, organic matter content, clay mineralogical composition amount and nature of clay.

Organisms :- Flora and fauna. Flora includes plant roots, micro-organisms, forest and grasses. Fauna means earthworms, ants, termite, rodents etc.Flora and fauna plays active role in the formation of soil.

It formed in the forest consists of relatively higher biological matter above the O horizon. Fauna plays an active role in the mixing and churning of such matters in soil.

Topography :- Influences through its effect on drainage, runoff, soil erosion and micro-climate .i.e. exposure of land surface to sun and wind. The depth of soil solum influenced by the degree of slope.

The soil of the upper slope are less clayer, lower in pH, soluble salts and organic matter content. Lighter in color and well drained in comparison to the soils at lower slope. Soil of the valley is generally deep and clayey.

Parent material :- It is the unconsolidated mass from which the solum develops. The physical, chemical and mineralogical properties of parent material have significant effect on soil formation.

These parent materials are grouped into three classes in soil science. Residual parent material, such parent materials are remained at same place for a longer time.

Soil formation takes long time from this parent material. Igneous rocks, sedimentary rock and metamorphic rock are the examples of this category.

Transported parent material, the breakages and pieces of rocks and minerals are transported from one place to other place by the agencies such as water, ice, air, gravity etc. Biological parent material, decomposed biological matters are termed as biological parent material.

Time :- It is the span of period from inception of soil development to present stage. ‘Soil formation‘ is a very slow process. Conditions that hasten the rate of soil development are warm and humid climate, forest vegetation, permeable and unconsolidated parent material, low in lime content, flat topography with good drainage.

Time factor has no relevance after the soil reaches its maturity. If the solum is removed by erosion or deposited over by a fresh transported parent material, a new cycle of soil formation takes place over the buried soil.

The soil forming factors are grouped into two :-

1. Passive soil forming factors comprises of parent materials, topography and time

2. Active soil forming factors consisting of climate and biosphere.

1. Passive soil forming factors

A.) Parent Material :- It is a most important initial soil materials that determines the soil profile development as well as physical properties of soil. The parent material has been defined as the state of soil system at zero of soil formation.

Parent materials influence soil formation with the intensity of weathering the nutrients that contain for the utilization by the plants and the particle sizes that contain sandy, rocky and clayes. The less development of soil, is the greater will be the effect of parent materials on the properties of the soil.

However the properties of well developed soil will also be greatly influenced by the parent material. Clay formation is favoured by parent materials containing high percentage decomposable dark material and less quartz.

The parent material may be transported from the place of their origin and re-deposited either before they become subject to alteration by soil formers or during the process of modification or by organic deposit. They are carried from one place to another and deposited by different agencies.

When the material transferred and deposited by water is known as alluvial. Colluvium is used for poorly sorted materials near the base of steep slope transported by the action of gravity. The materials blown by the wind are known as Loess (silty texture) and the aeolian sand when these are primary sand. The mineralogical composition of parent material also lead to the formation of different group of soil.

B.) Topography :- The Earth’s surface contour is called topography or relief. Topography influence the soil formation primarily through its associated water, temperature, soil erosion and microclimate relations. Out of total rainfall or precipitation a part of it percolates downward and a portion of it is lost at surface runoff.

In high hopes slopes positions like hill or mountain areas major portion of rain water is lost through runoff and it does not help much for the soil profile formation. During runoff the various soluble and insoluble materials deposited at the best of the slope.

In this way some of the soil formed on the upper portion of the slope and washed on with carrying most of the clay fractional and get deposited at the base of the slope with increasing clay content in the soil.

C.) Time :- The length of time required for soil formation is depend upon many inter-relation factors namely climate, nature of the parent material, relief etc. That time span from the inception or zero point of soil development to the present stage is called ‘age of soil’.

Soil formation is a very slow process. Age may vary from a few years to several years. Layers of soil tend to develop faster under hot, humid and forested conditions. Factors which cause delay in soil formation are extreme cold and dry climate, consolidated parent materials.

2. Active soil forming factors

A.) Climate :- Climate includes rainfall, temperature, humidity, aridity and wind. Different climate elements or components determined the water supply through rainfall or evaporation, temperature and total amount of heat supplied through solar radiation.

Climate is the most important factor that can influence the soil formation. Climate affect soil formation directly through the supply of water and heat and indirectly through different type of flora and funa forming different organic matter of different nature.

For an example, high temperature and moderate to high rainfall favours the formation of lateritic acid soil due to intense weathering and leaching of basic cation.

B.) Biosphere :- The activity of living plants and animal and the decomposition of their organic waste and residues have highly influence on soil formation as well as soil profile development.

The different types of vegetation like forest,trees and grass is having different root system kind of root exudates etc. also influence the soil formation. Vegetation particularly grasses reduce the runoff loss of water and increase soil water content which also influence the soil formation.

The microorganism play a important role in the decomposition of organic matter. The organic matter content of soil is also taken into consideration for the determination of different diagnostics soil horizons.

Soil Formation

Soil forming processes

The soil forming processes or pedogenic process are very complex because of simultaneously operating various chemical, mechanical and biological reaction. Soil is formed from weathering of rocks and minerals. Soil formation is a slow and complex process. Soil formation of one inch soil needs 800-1000 years.

There are generally two categories of soil forming process involved in the formation of soil. Basic or fundamental process and specific soil process.

A.) Basic or fundamental process

It includes :-

(1.) Addition of organic and mineral materials,

(2.) Loss of these materials from the soil,

(3.) Translocation of materials from one point to another within the soil column, and

(4.) Translocation of materials and organic substances within the soil.

B.) Specific soil formation

The basic or fundamental soil forming process bring about certain specific process by means of variety of reaction like Calcifications, Podzolization, Salinization, Gleization and Alkalization etc.


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