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Here is a compilation of essays on ‘Soil’ for Class 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Soil’ especially written for school and college students.
Essay on Soil
Essay Contents:
- Essay on the Meaning of Soil
- Essay on the Composition of Soil
- Essay on the Classification of Soil
- Essay on the Particle Density of the Soil
- Essay on the Specific Gravity of the Soil
- Essay on the Weight of Soil
- Essay on Soil Color
- Essay on the Influence of Climate on Soil
Essay # 1. Meaning of Soil:
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The term soil refers to the soft layer on the earth’s surface on which plants grow. Soil contains both organic and inorganic substances in large quantities. The organic substances known as humus in the soil are derived from decayed plant and animal remains. These are mixed with weathered particles of various rocks to constitute the soil.
The rocks exposed on the earth’s surface are moreover subjected to weathering caused by various chemical and physical reactions. Soil formation is generally a very slow process. For instance, it might take more than 1000 years for the formation of soil layer of about 2.5 cm thickness.
Of course, a lot depends on such factors as the composition of rocks and the influence of climate as well as the influence of plants and animals.
The factors responsible for transformation of rocks on the earth’s surface into soil may be grouped under three main headings:
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Physical factors:
Actions of water current, temperature, pressure, glacier and wind.
Chemical factors:
Actions of oxygen, salts and carbolic acid present in the atmosphere.
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Organic factors:
Actions of plant’s roots, man and animals.
Essay #
2. Composition of Soil:
There are number of ways for determining the composition of soil. One way is by colour. Generally, the colour of the soil depends on its chemical composition. The more the proportion of organic matters, the darker is the colour of the soil. Thus the colour may vary from near white, to brown and black.
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Proportion of iron, contained in the soil, might give it a red or yellow tinge. Soils in the marshes have greenish or bluish colour. In this soil some amount of iron also remains and is mixed up with the organic matters. Now-a-days, soil composition is determined by the size of grains in it, as, also, by the proportions of sand, silt and clay in the soil.
In this way, three varieties of soil can be identified, namely, Sandy soil, Clayey soil and Silty soil.
Sandy soil:
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The soil in which the diameter of the minute grains ranges between 0.05 and 1.0 mm and in which the proportion of sand is more than 60 per cent, is called sandy soil. In India, the soil of Thar Desert is of this type.
Clayey soil:
This type of soil is also known as loamy soil. The grains in this soil are very fine having diameter of less than 0.002 mm. The soil where the proportion of this kind of clay is more than 60 per cent is called clayey or loamy soil. The black cotton soil of Deccan belongs to this type.
Silty soil:
Silt is formed by a mixture of about equal parts of sand and clay. The soil in the valley of the Ganges and its deltaic region is of this type.
Mechanical Composition of Soil:
The mechanical composition of the soil is the weight percentage of the mineral matters that occurs in each of the specified size fractions of the soil.
Inorganic particles occurring in the soil have classified of the basis of their sizes as follows:
Stone is greater than 2 cm in diameter
Gravel is between 2 mm to 2 cm in diameter
Fine Earth is less than 2 mm in diameter
Fine Earth has been subdivided into the following groups called soil separates according to different systems.
(1) International System:
(2) United States Department of Agriculture (USDA) System:
USDA System emphasizes the sand fraction too much. Sand and silt fraction are equally important cording to the British system mentioned below.
(3) British System:
(4) The European:
System emphasizes sand. Silt and clay fraction as mentioned below.
Essay # 3. Classification of Soil:
Soils are formed from the weathering of rocks by various physical and chemical actions on them. These again are found to be composed in several horizons from the surface downwards. Generally, three soil horizons can be discerned from top to bottom.
1. A Horizon: Top or surface layer containing humus.
2. B Horizon: Intermediate soil.
3. C Horizon: Hard rocky layer.
In terms of origin, soils can be classified into two types, namely:
(a) Residual soil, and
(b) Transported soil.
(a) Residual soil:
This type of soil is generally formed in its place of origin. The weathered and crushed rocky materials mix with various organic substances to create residual soil. The black soil formed out of the rocks of the Deccan plateau is of this type.
(b) Transported Soil:
At times the weathered rocks particles are carried away by water current, glacier or wind and deposited elsewhere. These turn into soil. Such type of soil is called transported soil. Some of the alluvial soil in the river valleys and deltaic regions is an example of transported soil.
Similarly, the soil in the southern part of Canada is an example of transported soil formed by glaciers. The loess in northern China is an example of this type of soil formed by wind action.
Now-a-days again, the soil scientists classify the soil into three types:
(a) Zonal soil,
(b) Intra-zonal soil, and
(c) Azonal soil.
(a) Zonal soil:
This type of soil is formed due to prolonged influence of climate and actions of various plants. The land must have proper drainage for the formation of this type of soil. All the three horizons can be clearly seen in this type of soil. Some examples of zonal soil are the black soil and the red soil of the monsoonal regions of the Deccan plateau, and the chernozem and the brown soil of the temperate regions of Russia.
(b) Intra-zonal soil:
This soil is not very mature. Climate does not have much influence in its formation. This type of rather half mature soil is formed in the marshy area lying between two zonal soils. Since the soil is not mature enough or properly mixed, its drainage is not good.
Intrazonal soil is also formed from limestone and rocks containing salts. The soil formed by glaciers in the northern part of North America is of the intra-zonal type. This type of soil is also formed in the red soil regions of the Mediterranean and in parts of the Tundra region.
(c) Azonal soil:
This type of soil is composed solely of inorganic rocky ingredients such as gravel, sand and clay. It does not contain much of organic matter. It is found to develop in the foothill zones, at the end of the terminal moraines, in the deltas and in certain places of the deserts.
Azonal soil is, in fact, the first stage of soil formation. It comes into being before the intra-zonal and zonal soils are developed.
Within the framework of the above classification, new attempt is being made to find out more useful classification of soil. One such classification was put forward in the U.S.A. in 1960.
The main objects of this classification are:
(a) To arrange the soil types in a way so that these can be easily remembered;
(b) To establish relationship between different types and sub types of soil;
(c) To determine the stage of evolution of the soil; and
(d) To predict the quality of soil.
The soils are also classified differently into two main groups—pedelfers and pedocals. Pedelfers are found in humid climates of high latitude coniferous forests, mid-latitude deciduous forests and low latitude tropical forests. Pedocal soils are found in arid, semi-arid and sub-humid climates. The science of study of soil is called pedology.
Essay # 4. Particle Density of the Soil:
The density of soil solids is known as the particle density of the soil, which may be defined as the dry weight of soil solids per unit volume of dry soil solids. For example if one cubic centimeter of the dry soil solid weighs 2.65gms, then the particle density of the concerned soil is 2.65gms. Per cubic centimeter.
The particle density of the soil can be determined by adding the densities of the soil constituents as shown in the following formula.
Particle Density = D1P1 + D2P2………
Where D and P are the respective density and proportion of soil constituents 1, 2….
Example:
Find out the particle density of a soil of the following composition:
Solution:
Essay # 5. Specific Gravity of the Soil:
The specific gravity of the soil is the ratio of the weight of a given volume of soil solids to the weight of a equal volume of water. Since one cubic centimeter of water weighs one gram, specific gravity and particle density of the soil are numerically equal.
Since the specific gravity is a ratio it is dimensionless e.g. one cc of soil weighs 2.67gms in the above example, and one cc. of water weighs 1 gm. So the specific gravity of the soil is
2.67/1 = 2.67
The particle density and specific gravity of soils depends upon the densities and relative proportions of different soil constituents. They vary from 2.60 to 2.70, with an average value of 2.65gms/cc in the case of particle density and dimensionless in the case of specific gravity, of average mineral or inorganic soil.
Volume Weight of Soil or Bulk Specific Gravity of Soils:
It is defined as the ratio of the weight of a given volume of soil (This Vol. of soil = Vol. of soil solid + Vol. of pore space) to the weight of an equal volume of water.
Since the weight of one gram of water is one cc, the bulk density of soils and the volume weight of soils are numerically equal.
Essay # 6. Weight of Soil:
We know that the density of water is one, which means that one cubic centimetre of water weight one gram.
Convert cubic centimetre to cubic feet and gram to pounds (lb)
Since 1 cc = 0.0000353 cubic fit.
and 1gm = 0.002204365 pound (lb)
0.0000353 cu ft. of water weighs 0.0022043656 lbs.
or 1 cubic foot of water weighs = 0.002204365/0.0000353 = 62.44 lbs.
Hence Density of water is 62.44lbs per Cubic foot. In a similar way, if the bulk density of a soil is 1.2gm/cc, this means that 1 cc of the soil weighs 1.2gms.
Convert both cc and gms to cu.ft. and lbs. respectively. Then 0.0000353 cu.ft. of soil weighs 1.2 x 0.002204365 lbs. or
1 cubic foot of soil weighs = 1.2 x 0.002204365/0.0000353 = 1.2 x 62.44 = 74.928 lbs.
Hence the weight of one cubic foot of a dry soil is determined multiplying its bulk density, 1.2gms/cc, by 62.44 which is the weight of one cubic foot water is pounds.
Again in this example, if we convert cubic centimetre to cubic metre by dividing cubic centimetre by 1000000 and gram to kilogram by dividing gram by 1000.
Then 1/1000000 cubic meter of soil weight 1.2/100 kg.
Or 1 Cubic meter of soil weight 1.2/1000 x 10, 00,000 = 1200 kg.
Therefore the weight of one cubic metre of a soil can be determined simply by multiplying the soil bulk density in gm./cc by one thousand.
Weights of One Acre Foot of Soils and One Acre Furrow Slice of Soils:
One Acre foot of soil is the by volume of the soil of one Acre in Area and one foot in depth.
One Acre Furrow slice of soil is the volume of the soil of one acre in area and six inches in depth.
Volume of one Acre Foot of soil = 4840 x 9 x 1 = 43560 cu.ft. Volume of one Acre Furrow slice of soil = 4840 x 9 x ½ = 21780 cu.ft. If the average Bulk Density of the surface soil of one foot deep is 1.2gms /cc
Then wt. of 1 cu.ft. Soil = 1.2 x 62.44 = 74.928 cu.ft.
Wt. of one Acre Foot of soil = 43560 x 74.928 = 3263863.68lbs
And wt. of one Acre Furrow slice of soil = 21780 x 74.928 = 1631931.84 lbs.
Weight of one acre furrow slice of soil is 2 million pounds in the case of average mineral soils.
Weight of One Hectare Furrow Slice of Soils:
One hectare furrow slice of a soil is the volume of soil of one hectare in area and 15cms in depth. 1 hectare = 10000 square metres.
Volume of one Hectare Furrow slice of soil of 15 cm depth is
10000 x 15/100= 1500 cubic metres
If soil bulk density is 1.2gm/cc the weight of one cubic metre of soil is 1.2 X 1000 = 1200 kg.
The weight of one hectare furrow slice of soil is 1200 x 1500 = 1800000 kg of soil = 1.8 million kg;
Usually the weight of one hectare furrow slice of soil is 22 million kg in most cases.
Example:
The soil contains 0.003 per cent N. The bulk Density of the soil 1.2gms/cc. The wheat crop requires 80 kg of nitrogen per nitrogen per hectare. How much nitrogen is to be added to the soil per hectare.
Solution:
So the soil contains 54 kg of nitrogen per hectare. Then 80-54 = 26 kg of nitrogen is to be added to the hectare wheat field.
Tillage:
Soils are mechanically manipulated (for example, ploughed in order to make them favourable for the growth of more crops). The kinds of mechanical manipulations performed on soil to make them most favourable for the growth of crops are called Tillage of soils.
Soil Till:
The physical condition of the soil in relation to plant growth is called soil till. This means that soils which are in good till/allow rain water to enter in them rapidly. They are well drained and aerated, yet retain enough moisture for the growth of crops. They are mellow and friable and can be ploughed easily.
Ploughing:
The plough is the most important tillage implement for crop production. It cuts loose, granulates and inverts a certain volume of soil called furrow slice and also turns under of residues, weeds and green manures. The most important reason for ploughing the soil is loosening it so that seeds can germinate and crops grow. The curved mould board is used for turning under surface residues.
The Seed Bed:
The seed bed is the plough layer of soils where seeds can readily germinate and roots can develop and grow. The lower part of the seedbed should contain the finest soil granules and its upper part should contain the coarse soil granules. The immediate surface layer of the soil of 6 to 9 inches depth should be well aerated and should retain enough moisture for the germination of seeds and growth of crops.
Cultivation:
Cultivation is the tillage of soils after sowing the seeds or the germination of seeds. The fundamental reason for cultivation is to maintain the seedbed in good during the growth of crops. Soils are cultivated in order to control weeds and to make them well aerated. Poorer the soil structure, the greater will be the need for frequent loosening of the soil surface, and more rapid will be eventual deterioration of the soil structure.
Essay # 7. Soil Colour:
Causes of Soil Colour:
The Colour of soils is due to the colours of their constituents. For example, humus is black in colour. So a black coloured soil may be rich in humus. Ferric oxide is red in colour. So red soils are rich in it. Quartz is white or lighter in colour and clay is darker. So lighter coloured soils are richer in sand than the darker soils. Hence darker coloured soils are richer in clay and therefore more fertile than the lighter coloured soils.
Importance of Soil Colour:
Soil colour tells us about soil conditions. For example, red soils are rich in ferric oxide, highly weathered and of poor fertility. Black coloured soils are expected to be rich in humus and therefore fertile.
Darker coloured soils are richer in clay and therefore more fertile than the lighter coloured soils, because they can retain enough water and nutrients for plant growth.
Description of Soil Colour:
Soil colour is described by the following three variables:
(i) Hue is the dominant spectral colour.
(ii) Value is the relative lightness of the soil colour.
(iii) Chroma is the relative strength of purity of spectral colour. It increases with decreasing greyness.
All the three variables have been systematically arranged in a loose leaf note book called the Munsell colour chart. All the colour chips shown in each page of the Munsell colour chart are of same hue which is written at the top right hand corner of the page as shown in Fig. 4.4.
Vertically their value increases, and horizontally their chrome increases which means that vertically they become lighter and horizontally they become purer and less-grey. Opposite each page of the Munsell colour chips is a page where the corresponding English name of the concerned soil colour is written.
In order to describe the soil colour, it is compared with the colour chips of the Munsell colour chart. Its colour is described by the Munsell Notation of that colour chip with which it matches best.
Essay # 8. Influence of Climate on Soil:
From the factors outlined above, it is clear that the influence of climate is essential for soil formation. For example, the tropics, especially monsoonal regions, are marked by great heat and humidity. Moreover, in such regions the fluctuation of temperature between summer and winter is relatively more pronounced than in other regions.
These, together with abundant rainfall, induce easy weathering of rocks. The weathered rock particles and sediments in the uplands come to be deposited in the low-lying areas.
These are finally turned into soil. There is an abundant growth of vegetation in the tropical regions. The decomposed plants increase the fertility of soil. Soil forms easily in such regions. The soil of the western part of the Deccan plateau has been formed by the influence of monsoonal climate on lava rocks.
This is black in colour and very fertile. The red soil found in the eastern part of this plateau is rather dry. This soil was formed due to chemical reactions caused under dry winter and humid summer conditions.
The influence of wind is most important in soil formation in the hot desert regions. The wind blows away desert sands from one place to another. The heavier sand particles cannot be blown very far and hence, these are deposited as sand dunes near the desert.
But the finer sand particles are blown away to great distances and these give rise to a new type of soil, known as loess. The fertile parts of northern China are formed of fine sandy particles carried by wind from the Gobi desert.
The action of glacier in soil formation is clearly evident in the cold polar regions. Pebbles, sand, mud, etc., carried down by glacier form different types of soil in the lower regions. Fluctuation of temperature in the terminal parts of the glacier shatters the rocks into small bits and these ultimately form a new type of soil.
In the equatorial regions, plants grow quickly and hence, there are very thick forests. Forests prevent weathering of rocks. On the other hand, decomposed plants help in forming a type of rich and fertile soil. This type of soil is found in the Amazon and the Congo river valleys.
In the cold regions, the flow of river to the sea is prevented for months together by the freezing of water in the estuaries. As a result, marshes are formed in which various kinds of plants and weeds grow. The decomposed plant remains help in the formation of a new type of fertile soil. The soil in the Taiga region of Siberia is of this type.
The quality of the soil depends on the quantity of calcium, magnesium and potassium present in it. Plants take these elements from the soil with the help of roots. These are stored up in the branches and the leaves. When plant matters decompose, these elements are once again mixed with the soil and thus it adds to the fertility of the soil. Soil fertility depends a great deal on the proportion of organic substances in the soil.
The organic matters are derived from the remains of plants and animals. The decomposed plants and animal remains are mixed with soil humus by animals both chemically and physically. Creatures such as the earthworm and rat help in increasing soil fertility by their acts of bringing up fertile soil from below.
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