FORMATION OF SOIL

Soil is another natural resource, which is rather most precious of all resources, as it is essential for our survival as well as all other life forms. It is the top surface layer of the Earth’s crust. Rock particles make a large part of the soil.

It provides:

• Food and fodder

• Clothing

• Provides anchorage to the plants

• Water and minerals to the plants, and water for various human needs, irrigation and industry

• Home to a number of soil organisms.

Soil is formed from parent rock material over millions of years by a process called weathering.

Weathering occurs by.

Physical means, such as temperature, rain, wind, frost

Biological means, through the action of plants, animals and micro-organisms.

The other constituents which make up the soil are:

Mineral matter = 45%

Organic matter = 5%

Water = 25%

Air = 25%

Living organisms

Soils are derived from rocks by weathering. Percolating water is especially important in the formation of soils Young soils are stabilised when they become colonised by plants and animals. Eventually dead organic matter builds up and a mature soil as formed. Although the underlying parent rock influences the type of soil formed, the climate and vegetation are just as important.

The soil is classified on the basis of its nature and composition. The six major types of soil in our country are:

Alluvial soil – rich in loam and clay; the soil is highly productive.

Black soil – rich in clay; very fertile soil.

Red soil – rich in sand to loam; soil supports rain forests and grasslands.

Mountainous soil – rich in stone-sand; fertility low.

Desert soil – rich in sand; fertility low due to water scarcity.

Laterite soil – rich in clay (which is porous and rich in iron and aluminium hydroxides); rich in organic matter and fertility

FORMATION OF SOIL:

The process of soil formation is so slow that the soil is regarded as a non-renewable resource. Over long periods of time, thousands and millions of years, the rocks at or near the surface of the Earth are broken down by various physical, chemical and some biological processes. This is called weathering and results in formation of fine particles of soil.

Physical weathering:

Weathering caused by climatic factors is called physical weathering. The various climatic factors are:

Sun: The rocks get heated up and expand under the influence of solar radiations. Since all the parts of the rocks do not expand and contract at the same time, cracks appear in the rocks and ultimately the large rocks break up into smaller pieces.

Water: Water influences soil formation in the following two ways :

• The water gets into the cracks developed by the unequal heating of the different parts of the rocks. On freezing, the water expands in rock crevices and breaks the rocks.
• Hard rock wears away over long periods of time by the flowing water. Fast flowing river always carries big and small particles of rock downstream. These rocks rub against other rocks and result in the wearing of rocks into smaller particles. The water takes these particles of rocks and deposits them down its path.

Wind:Strong winds continuously rub against rocks, erode them and thus help in soil formation.

Biological weathering:

Living organisms like lichens, mosses, etc. influence the formation of soil.

• Lichens: They live on rocks and produce acids. The acids corrode the surface of rocks to form thin layer of soil.
• Mosses: Mosses later grow on such surfaces and cause the rock to break up further.
• Roots: The roots of trees enter the cracks and provide anchorage. In due course, roots grow bigger and force the cracks to widen.

Chemical weathering 

The rocks also undergo chemical weathering by processes like hydrolysis, hydration, oxidation and reduction.

Soil pollution:

Soil is also polluted through the polluted water and air. These pollutants are mixed into the soil through the rainy water. Such as H2 SO4 acid is formed by mixing of SO2 with rainy water in the air. The fertilizers are used to increase yield of the crops. Various types pesticides and weedicides etc. are sprayed over the crops. All these mixed with soil to produce harmful effects. The growth of plants inhibited or reduced due to this type of pollution and sometimes death also takes place. Excluding to these soil pollution is also caused by the disposal of house hold detergents, sewage, flowing oils, radioactive substances and hot water etc. the main substances of pesticides in soil pollutants are D.D.T. and weedicides 2, 4-D (2,4 di-chlorophenoxy acetic acid) 2,4,5-T (2,4,5, tri-chlorophenoxy acetic acid).

Control measures: soil pollution can be controlled through biological degradation of waste materials. The various carbonic materials are of agricultural waste, cattle dung etc. which can be minimized by the use of biogas plants which can produce energy also. Inspite all measures pesticides and weedicides should be used in limited quantity only when they are required. Bhopal Gas Tragedy is the best example of human hazard which took the life of many persons the tank of methyl isocyanate burst during the manufacturing of savin insecticide on 3rdDecember 1984.

Soil erosion :

• Fertility of soil depends on

• Presence of organic matter(humus) and nutrients, (ii) capacity of soil to retain water and air. A loamy soil is the best-suited for plant growth.

• The fertility of soil is threatened due to various activities of humans. The main threat to the fertility of soil is from soil erosion, which is the loss of soil due to wind or water flow.

Methods of Preventing Soil Erosion :

Prevention of soil erosion can be brought about by controlling the factors which cause soil erosion. The methods would thus be follows:

• Deforestation should be stopped, rather, trees should be planted (afforestation). Afforestation should be undertaken not only in areas already cut, but additional areas should be brought under plantation.
• To reduce the effect of strong wind in the fields, the boundaries of the fields should be planted with trees in two or three rows.
• To maintain the soil in its natural condition, it is advisable to grow different crops. Crop rotation helps to maintain the fertility of the soil. The water – holding capacity of the soil is also maintained by this method.
• Proper drainage and irrigation arrangements should be made in the fields.
• On the sloping areas in hills, strip cropping should be practiced, thereby reducing the steepness of the slopes and checking soil erosion.
• Strip – cropping means the planting of crops in rows or strips to check flow of water.