Topmost layer of the continental crust is called soil. It is made up of weathered particles, clay minerals, air, humus, water and micro-organisms. These constituents are present in soils in different composition and proportion due to varying environmental conditions. The composition of soil has been the basis of classification of soils.
According to the Indian Council of Agricultural Research
(ICAR), Indian soils are of eight types. This classification was put forth in
1956 on the basis of the All India Soil Survey Committee set up by the ICAR in
1953. The classification is based on three factors:
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Geological structure of soil
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Components of soil
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Colour of soil
The eight types of soils are as follows:
1.
Alluvial
2.
Red
3.
Black
4.
Laterite
5.
Forest soil
6.
Saline or alkaline
7.
Desert soil
8.
Peat or organic soil
Alluvial and peat soils are azonal (separated from their
region of origin) soils of India. Peat and saline soils are intra-zonal soils.
The rest are zonal soils. Here, primary minerals have become secondary
minerals. Magnetite is the primary mineral but it has become limonite, the
secondary mineral.
Alluvial soil covers 24 per cent of land of India. In area,
this soil is spread over 7.7 lakh sq km. It is a deposited soil caused by
rivers. There are four main regions of alluvial deposition in India. These are:
- Central plain: this plain is extended from
Indo-Pakistan border to Dimapur district of Nagaland. Dimapur is the only plain
district of Nagaland. It is spread over from the Siwalik foothills in the north
to upto 500 feet contour lines in south India.
-
Coastal plain: The demarcation line between
river plain and coastal plain is 500 feet contour lines.
-
Older alluvial plain in the western Rajasthan
districts of Ganganagar and Bikaner.
-
Inter-mountain alluvium: this type of soil is
found in Kashmir, Kangra and Doon valleys.
Alluvial deposits of central India are divided into three
types and each has regional name. These are Khadar, Bangar and Bhabar.
Khadar is Holocene alluvial deposits. It is characterised by
very fine clay deposits,mainly found in the flop prone valleys. Eastern Uttar
Pradesh, Bihar plain, almost all non-delta plain of West Bengal, lower
Brahmaputra valley, flood prone areas of eastern coastal plain and lower
valleys of Tapi and Narmada.
Bangar is an old alluvium. It is a loamy soil. It is found
in northwest plain, Rajasthan and western Uttar Pradesh. Bangar is also found
in Rajasthan and southern Punjab, where it is sandy loam soil. In western Uttar
Pradesh, clayey loam soil is found. Here
silt and clay are dominant.
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| Water body inside Ranthambore National Park at Sawai Madhopur in Rajasthan. (Photo: Prabhash K Dutta) |
Bangar is also called doab soil. It was deposited during
Pleistocene and early Holocene periods. Similar soil is found in the upper
Brahmaputra valley, Gujarat and upper plain of coastal regions.
Bhabar is terai soil. Greater content of sand and silt is
found in Bhabar soil. Similar soil is found in inter-mountain valley. It is a
soil known for coarse texture. They are just off alluvial fan, downwards.
Constitutional character of Indian soils: Indian alluvial
soil is deficient in nitrogen and humus. But lime and potash content is
adequate in alluvial soil. Lime content is very favourable in terai.
Significant phenomenon with alluvial soil is presence of finer grains which
make a region flat plain.
Alluvial soil is suitable for most of the crops. However,
Khadar is more suitable for rice and jute crops. Terai soil is suitable for
sugarcane while Bangar is favourable for those crops which depend on soil
moisture like wheat, sugarcane, oil seeds and pulses.
In the inter-mountainous valley (intermontane), the soil is
very suitable for sugarcane like in Doon valley and for paddy in other valleys
like Kashmir and Kangra’s where clay is the dominant constituent.
In plateau India, three more types of alluvium are found.
These are called red alluvium – in Cauvery and Vagai valleys, black alluvium –
Wainganga, Wardha, Narmada and Tapi valleys, and laterite alluvium – found in
Kerala coastal areas and Santhal Pargana region of Jharkhand.
The colour of red soil comes from the parental rocks. As the
parental rocks weather, particles dominating the rocks spread and give the red
alluvium its colour. Red alluvium is suitable for paddy but due to low rainfall
coarse grains are raised in Cauvery and Vagai basins. In blck alluvium region
paddy and cotton are raised. Laterite alluvium is commonly used for paddy
culture.
Red soil:
It has the second largest acreage in India. Its acreage is
about 5.2 lakh sq km. basically, it is the soil of archean plateau region of the country. Pre-Cambrian
structure are either igneous or the gneiss and schist. They have greater
content of iron which is greater in metamorphosed granite. Due to the presence
of iron ore, the weathered and loosened particles have gained the red colour.
Tamil Nadu has the largest acreage of red soil in India.
About two-third of Tamil Nadu is covered by red soil including red alluvium.
Other areas of red soil are, Travencore Hills of Kerala, Karnataka plateau
excluding a ribbon shaped area located between Bangalore and Mysore, Rayalseema
and Dandakaranya plateau area of Andhra Pradesh, Ratnagiri and Bhanda region
near Nagpur in Maharashtra, patches in Kutch, Eastern Rajasthan and Aravalis,
Durg and Bastar in Chhattisgarh, Balaghat and Gwalior in Madhya Pradesh, Jhansi
and Lalitpur in Uttar Pradesh, Dharawar rocks of Jharkhand, Singhbhum and
northern plateau of Odisha, plateau region on West Bengal, patches in Meghalaya
and Nagaland.
It has low moisture retaining capacity. Its humus content is
moderate. It is deficient in nitrogen and phosphorous. It has adequate to
excessive iron and moderate lime content. On the whole the red soil is not very
favourable for agricultural activities. Only rainy season is cultivable.
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| Dry forest vegetation inside the Ranthambore National Park. (Photo: Prabhash K Dutta) |
Red soil regions don’t have much prospect of irrigation
because the basement rock is granite. So, the ground water table is very deep.
Due to low humus after two-three years of agriculture or cultivation, there is
a sudden deterioration in land’s capability. By providing external inputs, its
capability can be maintained.
With inputs and irrigation facilities, coffee is cultivated
on red soil in Chikmagalur district of Karnataka. Even rubber plantation has
been successful here. The same experiment was replicated in Chitradurga and
Karwar of Karnataka. Kaiga nuclear power plant is located near Karwar in Uttara
Kannada district.
Chitradurga is famous for manganese ore while Coorg is known
for rubber and coffee plantation.
Black soil:
It is also called Regur in Maharashtra and Gujarat. India
has the largest acreage of black soil in the world. Total area under black soil
in India is 5.18 lakh square kilometres.
Black soil came into existence due to fissure eruption of
lava. It attained its present shape and texture due to weathering and decay of
basaltic structure.
Largest acreage of black soil is found in Maharashtra in
continuity with some patches in eastern Gujarat, where black alluvial soil is
dominant. Other areas under black soil include Malwa plateau of Madhya Pradesh,
an elongated stretch from Satpura and Panchmahal in Gujarat to Hoshangabad in
Madhya Pradesh, patches on the Pat plateau and Rajmahal hills in Jharkhand and
adjoining areas of Bihar and West Bengal, Telangana plateau, ribbon-shaped
plateau of Karnataka between Bangalore and Mysore, Coimbatore-Madurai uplands
in Tamil Nadu and patches on Meghalaya plateau.
On the basis of thickness and structural characteristics,
black soil is divided into four types:
Deep black
Medium black
Light black
Alluvial black
Deep black soil is found in the west central Maharashtra. It
is also found in Pune and Miraj districts. Miraj is in south Maharashtra. Here
is the thickness is greater compared to other types of black soil. Thickness
gives deep black colour to the soil. This is also found in Telangana region,
which also has greater thickness of soil. Though the deep black soil is suited
for agricultural activities, these regions don’t have intense cultivation due
to low rainfall. Both in Maharashtra and Telangana, the deep black soil regions
are drought prone areas.
Medium black soil is found over Malwa plateau, in
Karnataka’s black soil regions, central Maharashtra and Satpura regions of Gujarat
and Madhya Pradesh.
Light black soil is found in Gujarat, eastern Maharashtra,
Coimbatore-Madurai uplands of Tamil Nadu. Some of the most isolated areas in
peninsular India too have light black soil. It is not much thick giving the
light colour to the soil. The productivity of black soil varies according to
thickness – more the thickness, more productivity soil has.
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| A lion sleeping inside Delhi zoo. (Photo: Prabhash K Dutta) |
Alluvial black soil is a fertile soil. When the constituent
particles are considered, alluvial black soil has adequate lime, potash and
iron. But, it is low in humus. Water retaining capacity is high. Top structure
of soil is coarse. The coarseness of top soil attributed to dryness in the
upper layers. The bottom of the black alluvial soil has clay and silt, which
improve moisture retaining capacity.
Black soil is very suitable for dry-land farming. Cotton is
the main crop. After 1960, sugarcane has also emerged as the major crop on
black soil. Sugarcane requires more moisture. Consequently, tube-well
irrigation has developed in peninsular India.
In fact, there has been massive
exploitation of ground water especially in Maharashtra, where sharp
deterioration of ground water level has been found. This trend has adverse
impact on not only the capability of black soil but the ecology and the humans
also.
Laterite soil:
It is found in the laterite structure region of India with a
total area of 2.5 lakh sq km. it is found in Western Ghats, Anaimalai and
Cardamom Hills, laterite plateau in Kerala – which has maximum acreage of
laterite soil in India and about two-third of Kerala is covered with laterite
soil, Eastern Ghats with Odisha having the second largest acreage of laterite
soil, laterite structure of Karnataka particularly in Belgaum district of the
state, patches of similar soil in northern Tamil Nadu, Pat plateau of
Jharkhand, and also in Meghalaya plateau region.
Laterite soil consists of mixture of hydrated oxides of
aluminium and iron. Iron oxides are generally present in nodular form making
laterite gravelly soil. Laterite soil is poor in nitrogen, phosphoric acid,
potash and lime. It has adequate iron and aluminium but they don’t make the
soil fertile. Humus is not adequate in laterite soil. Consequently, it is not a
favourable soil for agriculture.
However, due to presence of gravelly alluvium, laterite soil
has become favourable for crops like groundnut. India’s most of the groundnuts are
cultivated on laterite soil, which is also suitable for coffee and spices in
high or moderate rainfall regions. Kerala is famous for spices grown on its
laterite and forest soils.
Tribes living in Western Ghats, Odisha, Jharkhand and
adjoining areas of Bihar grow coarse grains on this soil. Laterite soil needs
adequate external inputs of potash, nitrogen and phosphorous in 4:2: proportion
to make it suitable for cultivation. Also required is adequate and proper
irrigation. So, though its capability is low but productivity of the laterite
soil can be high with quality inputs.
Forest soil:
It is also known as forest and mountain soil of India. This
type of soil is internationally classified as mountain soil. Its acreage in India
is about 2 lakh sq km.
It is found on the mountain slopes. It has thin layer of
soil due to mountain slope. It has coarse structure. Clay, sand and even
weathered drop particles are mixed in this type of soil. It has adequate humus.
O1 layer is very rich. It is favourable for cultivation of those crops which do
not need greater penetration of roots.
The favourable factor with this soil is its air and water
drainage. This factor favours plantation cropping. India’s most of Jhoom
Farming is carried out on forest soil which is an unscientific practice.
What
is needed is to develop such land under plantation, food-grain and vegetation
farming.
Three important crops are grown on forest soil in northern
India – tea, apples and pineapples. In south India, tea and rubber are
cultivated. Nilgiri is famous for tea, Anaimalai for rubber plantation and
Cardamom slopes for spices.
Such soil is found on the slopes at an altitude of 500m –
3,000m. Entire Siwalik Himalaya is characterised by forest soil. Northeast India
too is covered with forest soil. Greater and Lesser Himalayas don’t have forest
soil.
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| A view of Carmona Zalor beach of Goa. (Photo: Prabhash K Dutta) |
Saline soil:
It is also known as saline and alkali soil. Its acreage in
India is about 1.4 lakh sq km. it has mainly developed in the inland basins of
the country. Patches is found in different parts of Rajasthan, western Gujarat,
southern Haryana, southwest Uttar Pradesh (in trans-Yamuna tract in Mathura and
Agra).
Saline soil emerges due to capillary action of the soil in
which salt comes onto the top layer of soil. It is mostly alluvial having
dominance of sand and clay. It is region of Bolson and Playa.
Alkali soil has greater accumulation of sodium chloride.
This is particularly evident in southern Haryana and southwest Uttar Pradesh
and in some parts of Bihar. In Uttar Pradesh and Bihar such soil is called
Usar. No agriculture is possible on Usar soil.
In Rajasthan and Uttar Pradesh, the soil’s quality is
improved by giving adequate water. Proper watering of alkali soil dissolves
salts present in the top soil forcing it to move downwards. With this, the
humus containing soil becomes favourable for agriculture. Short duration crops
are possible on alkali soil such nurtured.
The Rajasthan Agricultural Marketing Board experimented with
such soils with good effect. Areas with alkali soil are producing fruits,
flowers and also have some vegetation. Another way of improving this soil is to
develop water drainage through it.
This ensures that the landform is not
subjected to intense evapo-transpiration and thus retains some moisture. There
is no need for digging up canals through the region. Drip irrigation can be
used to grow flowers and fruits.
Desert soil:
It is mainly found in western Rajasthan and the Rann of Kutch. Total area under desert soil in India is about 1 lakh sq km.
It is basically a sandy soil. It has excess salt content.
Suspended salt and solid particles are in ample quantity in desert soil. Clay
is scarce. Consequently, the soil is not suitable for agriculture. Northern
part of the desert of India in Ganganagar, Bikaner, Kishangarh and some parts
of Barmer districts of Rajasthan has adequacy of clay. Humus is also available
there along with phosphorous.
Thus, the northern part of desert has some compositional
property of fertility. The real problem in this region is the shortage of
surface moisture. Horizon B provides adequate moisture due to which it is a
region of shrubs. Development of irrigation with Indira Gandhi canal has proven
the importance of this soil in India. Similar characters are found in Kalahari
desert and Arabian desert but not in Sahara or Australian desert.
Peat/Organic soil:
It is also named Peaty and Marshy soil. Its acreage in India
is about 1 lakh sq km. It is also known as delta soil. But, it is not found in
all delta regions of the country. It is found in those delta regions only which
are submerged during high tide.
Deltas formed by Ganga, Mahanadi, Brahmi, Godawari and some
parts of Krishna delta have peat soil. Cauvery delta does not have much peat
soil. In some parts, it is also called
mangrove delta soil.
It is the region of clay and mud. It has suspended solids of
salts and excess of moisture.
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| A tiger taking rest at Bannerghatta National Park in Bengaluru. (Photo: Prabhash K Dutta) |
Due to excessive moisture content and salt, the
region has not been conducive for bacterial activities that are essential to
decompose organic components of the soil. The soil carries wooden pieces,
skeletons of plants, dead organic tissues and the like.
Owing to lack of decomposition of dead organic materials, it
has no humus. No nitrogen content is present in the soil. Excessive moisture
and salt have made it infertile type of soil. Only hydrophytes which have
tolerance for salts grow in these regions.
Peat soil regions can be, however, developed for coconut
plantation farming. Only problem is that coconut plantation needs much more
content of sand in soil while peat has more clay than sand.
