Soil
Soil is the most important layer of
the earth’s crust. It is a valuable resource. Soil is the mixture of rock
debris and organic materials which develop on the earth’s surface. The major factors
affecting the formation of soil are relief, parent material, climate,
vegetation and other life-forms and time. Besides these, human activities also
influence it to a large extent. Components of the soil are mineral particles,
humus, water and air. If we dig a pit on land and look at the soil, we find
that it consists of three layers which are called horizons. ‘Horizon A’ is the
topmost zone, where organic materials have got incorporated with the mineral
matter, nutrients and water, which are necessary for the growth of plants.
‘Horizon B’ is a transition zone between the ‘horizon A’ and ‘horizon C’, and
contains matter derived from below as well as from above. ‘Horizon C’ is
composed of the loose parent material. This layer is the first stage in the
soil formation process and eventually forms the above two layers. This
arrangement of layers is known as the soil profile. Underneath these three
horizons is the rock which is also known as the parent rock or the bedrock. In
ancient times, soils used to be classified into two main groups – Urvara and
Usara, which were fertile and sterile. In the 16th century A.D.,
soils were classified on the basis of their inherent characteristics and
external features such as texture, colour, slope of land and moisture content
in the soil. . Based on texture, main soil types were identified as sandy,
clayey, silty and loam, etc. On the basis of colour, they were red, yellow,
black, etc. The National Bureau of Soil Survey and the Land Use Planning an
Institute under the control of the Indian Council of Agricultural Research
(ICAR) did a lot of studies on Indian soils. United States Department of
Agriculture (USDA) Soil Taxonomy.
Soil types are classified according to many more factors. They are classified on the basis of colour, depth, pH, productivity, texture and process of formation.
Soil types are classified according to many more factors. They are classified on the basis of colour, depth, pH, productivity, texture and process of formation.
Soil types according to depth are as follows:
1) Shallow Soil - Soil depth less than 22.5cm. Only shallow rooted crops are grown in such soil, e.g. Paddy, Nagli.
2) Medium deep soil - Soil depth is 22.5 to 45cm. Crops with medium deep roots are grown in this type of soil e.g. Sugar cane, Banana, Gram.
3) Deep soil - Soil depth is more than 45cm. Crops with long and deep roots are grown in this type a soil e.g. Mango, coconut
1) Shallow Soil - Soil depth less than 22.5cm. Only shallow rooted crops are grown in such soil, e.g. Paddy, Nagli.
2) Medium deep soil - Soil depth is 22.5 to 45cm. Crops with medium deep roots are grown in this type of soil e.g. Sugar cane, Banana, Gram.
3) Deep soil - Soil depth is more than 45cm. Crops with long and deep roots are grown in this type a soil e.g. Mango, coconut
On the basis of genesis, colour,
composition and location, the soils of India have been classified into:
(i) Alluvial soil
(ii) Black soil
(iii) Red and Yellow soil
(iv) Laterite soil
(v) Arid soil
(vi) Saline soil
(vii) Peaty soil
(viii) Forest soil.
Alluvial Soil
Alluvial soils are widespread in the
northern plains and the river valleys. These soils cover about 40 per cent of
the total area of the country. They are depositional soils, transported and
deposited by rivers and streams. The alluvial soils vary in nature from sandy
loam to clay. They are generally rich in potash but poor in phosphorous. In the
Upper and Middle Ganga plain, two different types of alluvial soils have
developed, viz. Khadar and Bhangar. Khadar is the new alluvium and is deposited
by floods annually, which enriches the soil by depositing fine silts. Bhangar
represents a system of older alluvium, deposited away from the flood plains.
Both the Khadar and Bhangar soils contain calcareous concretions (Kankars).
These soils are more loamy and clayey in the lower and middle Ganga plain and
the Brahamaputra valley.
Black Soil
Black soil covers most of the Deccan
Plateau which includes parts of Maharashtra, Madhya Pradesh, Gujarat, Andhra
Pradesh and some parts of Tamil Nadu. In the upper reaches of the Godavari and
the Krishna, and the north western part of the Deccan Plateau, the black soil
is very deep. These soils are also known as the ‘Regur Soil’ or the ‘Black
Cotton Soil’. During the dry season, these soil develop wide cracks. Thus,
there occurs a kind of ‘self ploughing’. Chemically, the black soils are rich
in lime, iron, magnesia and alumina. They also contain potash. But they lack in
phosphorous, nitrogen and organic matter. The colour of the soil ranges from
deep black to grey.
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Red and Yellow Soil
Red soil develops on crystalline
igneous rocks in areas of low rainfall in the eastern and southern part of the
Deccan Plateau. Along the piedmont zone of the Western Ghat, long stretch of
area is occupied by red loamy soil. Yellow and red soils are also found in
parts of Odisha and Chattisgarh and in the southern parts of the middle Ganga plain.
The soil develops a reddish colour due to a wide diffusion of iron in
crystalline and metamorphic rocks. It looks yellow when it occurs in a hydrated
form. The fine-grained red and yellow soils are normally fertile, whereas coarse-grained
soils found in dry upland areas are poor in fertility. They are generally poor
in nitrogen, phosphorous and humus.
Laterite Soil
Laterite has been derived from the Latin word
‘Later’ which means brick. The laterite soils develop in areas with high
temperature and high rainfall. These are the result of intense leaching due to
tropical rains. With rain, lime and silica are leached away, and soils rich in
iron oxide and aluminium compound are left behind. These soils are poor in
organic matter, nitrogen, phosphate and calcium, while iron oxide and potash
are in excess. Hence, laterites are not suitable for cultivation; however,
application of manures and fertilisers are required for making the soils
fertile for cultivation. Red laterite soils in Tamil Nadu, Andhra Pradesh and
Kerala are more suitable for tree crops like cashewnut. Laterite soils are
widely cut as bricks for use in house construction. The laterite soils are
commonly found in Karnataka, Kerala, Tamil Nadu, Madhya Pradesh and the hilly
areas of Odisha and Assam.
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Arid Soil
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Arid soils range from red to brown
in colour. They are generally sandy in structure and saline in nature. In some
areas, the salt content is so high that common salt is obtained by evaporating
the saline water. Nitrogen is insufficient and the phosphate content is normal.
Lower horizons of the soil are occupied by ‘kankar’ layers because of the
increasing calcium content downwards. The ‘Kankar’ layer formation in the
bottom horizons restricts the infiltration of water, and as such when
irrigation is made available, the soil moisture is readily available for a
sustainable plant growth. Arid soils are characteristically developed in
western Rajasthan. These soils are poor and contain little humus and organic
matter.
Saline Soil
They are also known as Usara soils.
Saline soils contain a larger proportion of sodium, potassium and magnesium,
and thus, they are infertile, and do not support any vegetative growth. Their structure
ranges from sandy to loamy. They lack in nitrogen and calcium. Saline soils are
more widespread in western Gujarat, deltas of the eastern coast and in
Sunderban areas of West Bengal. . In the areas of intensive cultivation with
excessive use of irrigation, especially in areas of green revolution, the
fertile alluvial soils are becoming saline. Excessive irrigation with dry
climatic conditions promotes capillary action, which results in the deposition
of salt on the top layer of the soil. In such areas, especially in Punjab and Haryana,
farmers are advised to add gypsum to solve the problem of salinity in the soil.
Peaty Soil
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They are found in the areas of heavy
rainfall and high humidity, where there is a good growth of vegetation. Organic
matter in these soils may go even up to 40-50 per cent. These soils are
normally heavy and black in colour. At many places, they are alkaline also. It
occurs widely in the northern part of Bihar, southern part of Uttaranchal and
the coastal areas of West Bengal, Orissa and Tamil Nadu.
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Forest Soil
As the name suggests, forest soils
are formed in the forest areas where sufficient rainfall is available. The
soils vary in structure and texture depending on the mountain environment where
they are formed. In the snow-bound areas of the Himalayas, they experience
denudation, and are acidic with low humus content. The soils found in the lower
valleys are fertile.
SOIL DEGRADATION
Soil degradation can be defined as
the decline in soil fertility. Soil degradation is the main factor leading to
the depleting soil resource base in India. The degree of soil degradation
varies from place to place according to the topography.
SOIL EROSION
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The destruction
of the soil cover is described as soil erosion. The soil forming processes and
the erosional processes of running water and wind go on simultaneously. Wind
and water are powerful agents of soil erosion because of their ability to
remove soil and transport it. Regions with heavy rainfall and steep slopes,
erosion by running water is more significant. Water erosion which is more
serious and occurs extensively in different parts of India, takes place mainly
in the form of sheet and gully erosion. Gullies deepen with rainfall, cut the
agricultural lands into small fragments and make them unfit for cultivation. A
region with a large number of deep gullies or ravines is called a badland
topography. Ravines are widespread, in the Chambal basin. The country is losing
about 8,000 hectares of land to ravines every year. Deforestation is one of the
major causes of soil erosion. Plants keep soils bound in locks of roots, and
thus, prevent erosion. They also add humus to the soil by shedding leaves and
twigs. Forests have been denuded practically in most parts of India but their effects
on soil erosion are more in hilly parts of the country.
According to estimates, about half of the total land of India is under some degree
of degradation. Every year, India loses millions of tonnes of soil and its
nutrients to the agents of its degradation, which adversely affects our
national productivity.
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Soil
Conservation
Soil
conservation is a methodology to maintain soil fertility, prevent soil erosion and
exhaustion, and improve the degraded condition of the soil. Soil
erosion is essentially aggravated by faulty practices. The first step in any
rational solution is to check open cultivable lands on slopes from farming.
Lands with a slope gradient of 15 - 25 per cent should not be used for
cultivation. Over-grazing and shifting
cultivation in many parts of India have affected the natural cover of land and
given rise to extensive erosion. It should be regulated and controlled by educating
villagers about the consequences. Contour
bunding, Contour terracing, regulated forestry, controlled grazing, cover cropping,
mixed farming and crop rotation are some of the remedial measures which are
often adopted to reduce soil erosion. Lands not suitable for cultivation should
be converted into pastures for grazing. Experiments have been made to stabilise
sand dunes in western Rajasthan by the Central Arid Zone Research Institute
(CAZRI). The Central Soil Conservation Board, set up by the Government of
India, has prepared a number of plans for soil conservation in different parts
of the country. These plans are based on the climatic conditions, configuration
of land and the
social behaviour of people.
By
Vinay Kumar
social behaviour of people.
Soil of
India: Types, ph Range and Regional Distribution
Type
|
Features (formation, composition)
|
Distribution
|
Predominant Crops
|
Alluvial Soil
pH range: 6.5-8.4
|
Two types:
Khaddar- light in
color, more siliceous in composition and composed of newer deposit
Bhaggar- the older
alluvium is composed of lime nodules and has clayey composition. It is dark
in color.
|
Ganga and
Brahmaputra river valleys ; deltas of Godavari and Krishna ; plains of
Uttar Pradesh, Uttaranchal, Punjab, Haryana , West Bengal and Bihar ; Coastal
strip of peninsular India
|
Rice , Wheat,
Sugarcane,
|
Desert Soil
pH range:
7.6-8.4
|
Contain a high
percentage of soluble salts but are poor in organic matter; rich enough in
phosphate though poor in nitrogen
|
Rajasthan, Northern
Gujarat and southern Punjab
|
Wheat, grams, melon,
bajra (with irrigation)
|
Black Soil
pH range: 6.5-8.4
|
The soils are
derived from basalts of Deccan trap. They derive their name from their black
color which may be owing to presence of titanium, iron.
Consist of calcium
and magnesium carbonates; high quantities of iron, aluminum, lime and
magnesia and poor percentage of phosphate, nitrogen and organic matter
|
Maharashtra and
Malwa plateaus , Kathiawar peninsula, Telengana and Rayalasema region of
Andhra and northern part of Karnataka
|
Cotton ,
millets(include Jowar ,Bajra and ragi ), tobacco, sugarcane
|
Mixed Red and Black Soil
pH range: 6.5-7.5
|
Scattered in
Peninsular India
|
Millets, wheat
|
|
Red Soil
pH range: below 5.5-7.5
|
Mainly formed due to
decomposition of ancient crystalline rocks like granites and gneisses and
from rock type rich in minerals such as iron and magnesium. Generally poor in
nitrogen, phosphorus, humus but rich in potash. Siliceous and aluminous in
nature. Clay fraction of the red soils generally consists of Kaolinitic
minerals.
|
Eastern parts Deccan
plateau, southern states of Kerala , Tamil Nadu and Karnataka and Chota
Nagpur plateau
(Jharkhand)
|
Wheat, Rice , Cotton
, Sugarcane, pulses
|
Grey and Brown
pH range: 7.6-above 8.5
|
Semi- arid tract of
Rajasthan and Gujarat
|
Cotton, oilseeds
|
|
Laterite Soil
pH range:
below 5.5
|
Composed mainly of
hydrated oxides of iron and aluminum; loss of silica from the soil profile
|
Assam hills, hill of
summits of Kerala and Karnataka and eastern Ghats region of Orissa
|
Coffee, rubber,
cashew nut, tapioca
|
Mountain soil
pH range: 5.0-6.5
|
Coniferous forest
belt of Jammu and Kashmir, Himachal Pradesh, Uttaranchal and Sikkim
|
Fruit, tea
|
Indian
Soils with Percentage of Coverage
Soil
Types
|
Percentage of Total Area
|
Alluvial
soils
|
22.16
|
Black
Soils
|
29.69
|
Red and
yellow Soils
|
28.00
|
Laterite
Soils
|
2.62
|
Arid
Soils
|
6.13
|
Saline
soils
|
1.29
|
Peaty
and Organic Soils
|
2.17
|
Forest
|
7.94
|
By
Vinay Kumar
