Piles of soil with various compositions used for levelling the terrain (Photo credit: Wikipedia)
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SOILS IN INDIA
What is soil?
Soil is the uppermost thin layer of Earth’s crust which consists of a loose mixture of small rock particles and rotting organic matter that covers much of the world’s land surface. Soil is the medium in which plants grow and thus it supports the lives on earth.
How are soils formed?
Soils are formed due to the weathering of rocks.
Write a short note on soil formation.
Soil formation is a very long process. It begins with the weathering of rocks into small fragments. The rocks are also worn away by the agents of erosion like river, wind, sea and glacier. The sediments and tiny rock particles are then deposited by the agents of erosion. The accumulation of such sediments over the ages forms soil. Eventually, the plants that grow on the soil shed their leaves, which decay to form the topmost layer of soil called ‘humus’.
Name two factors which determine the types of soil found in India.
Climate and Topography
Categorize the soils of India on the basis of their formation.
Residual Soil and Transported Soil
India is primarily an agricultural country. The success of agriculture depends upon the fertility of soils. The soils of India are classified into the following main groups depending upon the rock cover and climatic conditions.
The major soil groups are:
Black soil, Red soil, Laterite soil, Alluvial soil,
and (-not in syllabus- Desert soil, Mountain soil- not in syllabus-)
Black soil is formed by the weathering of igneous rocks and the cooling of lava after a volcanic eruption.
They are mainly found over the Deccan lava tract, i.e. the Deccan Trap/Deccan Plateau, which includes Maharashtra, Madhya Pradesh, Gujarat, Andhra Pradesh, and parts of Tamil Nadu. These soils are found in the river valleys of Narmada, Tapi, Godavari and Krishna. These soils have been formed due to the weathering of the lava rocks. This soil is also known as regur soil and black cotton soil. These soils are rich in lime, iron, magnesia and alumina but lack in the phosphorus, nitrogen and organic matter.
The black soil is very deep in the upper parts of Godavari and Krishna and in the north-western part of Deccan Plateau.
* Formed in situ, i.e. found at their place of origin/formation, over the underlying rocks.
* Fine textured and clayey in nature; deep and impermeable.
* Has high quantities of lime, iron, magnesia, carbonates, alumina, and potash (LIMCAP) and generally poor percentage of phosphorous, nitrogen and organic matter. Contains soluble salts in small quantities.
* Generally black in colour as it is formed from weathered lava rocks; the color of the soil may range from deep black to chestnut-brown to grey.
* Very clayey and therefore highly water retentive. Due to high clay content, these soils expand when wet and become difficult to plough. During dry season, black soils shrink and develop wide cracks which help in air circulation.
* Soil is very fertile in most of the places.
* May need irrigation support and help of fertilizers for cultivation.
* Suited for dry farming as it does not require much moisture, i.e. since it is moisture retentive.
* Spread over an area of 5.4 sq. km., i.e. 16.6 % of the total land area of the country.
(Name two characteristic properties of black soil: moisture retentiveness and self-ploughing property)
Suitable for growing cereals, rice, wheat, jowar, oilseeds, citrus fruits and vegetables, tobacco and sugarcane.
These soils are found in Chhota Nagpur plateau, Telangana, Nilgiri Hills, Tamil Nadu, Karnataka, Andhra Pradesh and periphery areas of Deccan Plateau. These soils have been formed due to decomposition of underlying igneous rocks under heavy rainfall. These are suitable for the cultivation of millets, pulses, linseed, tobacco etc. These soils are poor in lime, nitrogen and humus.
* Red soils are reddish in colour due to the presence of iron. This type of soil is found in south India as well as in the Chhota Nagpur Plateau.
* Formed due to weathering of ancient crystalline and metamorphic rocks.
* Parent rocks are acid granites and gneisses.
* Occupy an area of about 3.5 lakh sq km – 10.6% of the total land area of the country.
* These are transported type soils.
* Found at a depth of 500 meters.
* Coarsest in the upper section of the valley, medium in the middle and finest in the delta region.
* Are mostly light to dark in colour depending on new or old alluvium.
* Rich in potash and become fertile with the proper use of fertilizers and irrigation.
* Deficient in nitrogen, lime, magnesia, humus and phosphate.
* Found mainly on the plateau region of peninsular India, the Malwa Plateau and the Chhota Nagpur Plateau.
* It covers almost the whole of Tamil Nadu, Karnataka, Andhra Pradesh, and south-eastern Maharashtra, eastern parts of Madhya Pradesh, parts of Orissa, Jharkhand and Bundelkhand.
* They practically encircle the entire black soil region on all sides. They extend northwards in the west along with the Konkan Coast of Maharashtra.
* Red due to its very high iron content.
* Colour varies from red to brown, chocolate and yellow.
* Are porous, friable in nature.
* Loose and aerated.
* Contains soluble salts in small quantities.
LATERITE SOIL Laterite = brick (Latin word)
Laterite soils are found on the highland areas of the plateau. These are found in Karnataka, Kerala, Tamil Nadu and hilly regions of Assam, Rajmahal hills and Chhota Nagpur plateau. These are shallow, acidic and less fertile soils. These soils are poor in lime but rich in iron. So these are suitable for plantation of crops like tea, rubber, coffee etc. Since low fertility because of high acidity and low moisture retention, manuring and other activities are required to make them suitable for growing crops such as ragi, rice and sugarcane. Paddy is grown on lower elevations whereas tea, cinchona, rubber, and coffee are grown on higher elevations. It is also suitable for building purpose.
These soils are formed under conditions of high temperature and heavy rainfall with alternate wet and dry periods. Thus its formation takes place strictly under monsoon conditions. Residual soils formed by leaching in areas of heavy rain. Leaching is a process in which the (soluble) nutrients get percolated down below the soil due to heavy rainfall; thus leaving the top soil infertile, also called DESILICATION. Laterite soils are found in elevated areas which receive very high rainfall. As a result, the top soil gets washed away. This process is called leaching. The soil, therefore, loses its fertility to a great extent.
* It covers an area of about 2.4 lakh sq km. These soils are found in the north eastern state of Meghalaya in India.
* Is of coarse texture, soft and friable.
* Is red due to the presence of iron oxide which is formed by leaching. The soluble plant foods like potash are removed from the top soil leaving alumina and iron oxide.
* Is a porous soil, silica is removed from it by chemical action.
* Is poor in lime and magnesium, and deficient in nitrogen.
* Laterite soil is formed by weathering of lateritic rocks, low temperature and heavy rainfall with alternating dry and wet periods.
* It does not retain moisture and hence is not fertile. It suits only special crops like tapioca, cashew nuts, etc.
* It is acidic in nature as alkalis are leached.
TWO TYPES: Upland Laterites and Lowland Laterites
Upland Laterite is formed over hills and uplands. When they are transported by steams towards lowlands, they, i.e. such transported soils, are known as Lowland Laterites.
ALLUVIAL SOILS (Riverine soil)
It covers about 40 percent of land area of the country. They are depositional soils, transported and deposited by rivers and streams. Through a narrow corridor in Rajasthan, they extend into the plains of Gujarat. These soils are formed by the deposition of fine sediments and silt by the rivers along their banks. In India, alluvial soils are mostly found in the Great Northern Plains, the coastal plains and river deltas
In Peninsular region, they are found in deltas of the east coast and in the river valleys. These soils originate from the transported alluvium brought by the rivers. They can be divided into two types:
1. Young Khadar soils: these are newer alluvium of sandy, pale brown composition, found in lower areas of valley bottom which are flooded almost every year. It is non porous, clayey and loamy.
2. Old Bhangar soils: these consist of older alluvium of clayey composition and are dark in colour. They are coarse in nature; contain kankar (lime nodules), pebbles, and gravels. They are found 30 m above flood level of the rivers. They represent the ‘riverine alluvium’ brought down by Sutlej, Yamuna, Ghagra and other rivers of Indo-Gangetic Plains.
These soils are the most widespread soils covering an area of 8 lakh sq. km from Punjab to Assam. These are found in the river basin, flood plains and coastal areas. These soils are deep soils rich in potash but poor in nitrogen. These soils are covering 22.16 per cent of total area of India. The major rivers which are contributing in the formation of the alluvial soils are :Ganga river, Brahmaputra river, Sutlej river, Mahanadi river , Godavari river , Krishna river
Alluvial soils of two types: deltaic coastal and inland alluvial. Found in Uttaranchal, U.P., Bihar, W. Bengal, Punjab, and Haryana & Assam. In south, found in the plains and deltas in Andhra Pradesh, Orissa, and Tamil Nadu.
* Alluvial soils though differ greatly in texture, are very fertile on whole.
* Respond well to irrigation and manuring.
* Good for both rabi and kharif crops.
* Suitable for wheat, sugarcane, rice, cotton and oilseeds.
* In delta region, they are ideal for jute cultivation.
* Useful for agriculture since it is fertile.
* Soil is rich in potash and lime but poor in nitrogen and humus.
DENUDATION is the process of wearing away of the earth’s surface. There are many agents of denudation.
1. Rivers 2.Glaciers 3.Winds 4.Sea waves, etc.
SOIL EROSION – Soil erosion is the main problem of our country. It is on the increase in recent years
Main reasons: Running water, overgrazing, faulty methods of agriculture, over irrigation, wind, and men, plants and animals.
Soil erosion happens when particles of soil come loose and are carried away by water or the wind. When it rains so much that the water cannot seep into the soil fast enough, the extra water flows down the slope, carrying soil particles with it. Many agricultural soils are easily eroded. The erosion problem is likely to be more severe on certain types of soils, on steep slopes, where there is intense rainfall, and where the vegetation is removed. Indirectly soil erosion helps in the soil forming because from wherever the soil is removed it is deposited elsewhere. However it disturbs the agricultural pattern and should be prevented.
There are several ways in which soil erosion takes place due to running water.
(a) SPLASH EROSION: Splash erosion where the soil is pulverized by the impact of heavy drops and hailstones as in case of conventional rainfall.
(b) SHEET EROSION: Removal of thin layer of soil from a large area. In sheet erosion a thin layer of soil is removed from a large area.
(c) GULLY EROSION: Large, wide channels carved by running water. As a rule of thumb, a gully is large enough that it cannot be smoothed out with conventional tillage equipment.
(d) RILL EROSION: A series of small channels on a slope carved by running water.
Splash erosion or rain drop impact represents the first stage in the erosion process. Splash erosion results from the bombardment of the soil surface by rain drops. Rain drops behave as little bombs when falling on exposed or bare soil, displacing soil particles and destroying soil structure. Studies have shown that splashed particles may rise as high as 0.6 meters above the ground and move up to 1.5 meters horizontally. Splash erosion results in the formation of surface crusts which reduce infiltration resulting in the start of runoff.
It is the first stage in the erosion process. It results from the bombardment of the soil surface by raindrops .It is the primary cause of soil detachment and soil disintegration. It means that resettled sediment blocks soil pores resulting in surface crusting and lower infiltration.
Sheet erosion occurs when thin layers of the topsoil are moved by the force of the runoff water, leaving the surface uniformly eroded. Cultivation on hill slopes is the main cause of soil erosion.
Rill erosion is caused by runoff water when it creates small, linear depressions in the soil surface. These are easily removed during land tillage.
Unlike rill erosion, gullies are too deep to be removed during normal cultivation with ordinary farm implements. They are formed from small depressions, which concentrate water and enlarge until several join to form a channel. The deepening channel undermines the head wall, which retreats uphill. The gully then widens as the side-walls are worn back.
Sea or Shore erosion
* Tidal waters of sea cause considerable damage to the soil along the sea-coast.
* Powerful waves dash against sea-coast and break hanging cliff rocks.
* Broken material is then removed by the retreating sea waves.
* This type of erosion is seen throughout the eastern and western coasts of India.
Typical features of coastal erosion: from the initial cracks in less resistant rock through to arches, stacks, and stumps that can occur as erosion progresses.
STREAM BANK EROSION:
Stream bank erosion is common along rivers, streams and drains where banks have been eroded, sloughed or undercut. However, it is important to remember that a stream is a dynamic and constantly changing system.
It is natural for a stream to want to meander, so not all eroding banks which are slowly eroding are “bad” and in need of repair. Generally, stream bank erosion becomes a problem where development has limited the meandering nature of streams, where streams have been channelized, or where stream bank structures (like bridges, culverts, etc.) are located in places where they can actually cause damage to downstream areas. Stabilizing these areas can help protect watercourses from continued sedimentation, damage to adjacent land uses, control unwanted meander, and improvement of habitat for fish and wildlife.
Streams and rivers change their courses by cutting one bank and depositing the silt on the others. During flash floods, the damage is much accelerated.
Prevalent in the flood plains of Ganga, Yamuna, and other rivers. As a result, large areas of agricultural land in the states of U.P., Rajasthan, and M.P. have been transformed into ravines.
Wind erosion refers to the movement and deposition of soil particles by wind. It occurs when soil devoid of vegetation is exposed to high velocity wind. Wind moves soil particles 0.1 – 0.5 mm in size in bouncing or hopping fashion and those greater than 0.5 by rolling. The former is known as saltation and the latter as soil creep. The particles less than 0.1mm or the fines particles detach into suspension. In fact wind erosion is
most visible in the suspension stage, as dust storms or subsequently as deposition along fence lines and across roads. Soil erosion by wind occurs on extensive flat lands which are subject to windy dry season for part of the year. The upper soil surface becomes loose and susceptible to wind erosion due to lack of moisture.
Due to overgrazing, wind erosion occurs as the soil devoid of vegetation is directly exposed to the wind.
FAULTY METHODS OF AGRICULTURE
i) Shifting agriculture as in Northeast India
ii)Lack of crop rotation
iii) Wrong ploughing
In agriculture, leaching may refer to the loss of water-soluble plant nutrients from the soil, due to rain and irrigation. Soil structure, crop planning, type and application rates of fertilizers, and other factors are taken into account to avoid excessive nutrient loss. Leaching may also refer to the practice of applying a small amount of excess irrigation where the water has a high salt content to avoid salts from building up in the soil (salinity control). Where this is practiced, drainage must also usually be employed, to carry away the excess water. Leaching is an environmental concern when it contributes to groundwater contamination. As water from rain, flooding, or other sources seeps into the ground, it can dissolve chemicals and carry them into the underground water supply. Of particular concern are hazardous waste dumps and landfills, and, in agriculture, excess fertilizer and improperly stored animal manure.
SOIL EROSION DUE TO HUMAN FACTOR:
* Loss of forest cover – annual rate about 47,500 hectares
* Leads to sheet erosion on hilly slopes because water instead of sinking into the ground washes the soil down.
* In the second stage, in the absence of vegetation cover and washing off of the absorbent top soil, rills begin to appear on the landscape
* In the third stage, the water runoff during heavy rains may develop deep grooves causing Gully erosion.
* The Outer Himalayas, the Western & Eastern Ghats are subjected to deforestation by man.
* These areas receive heavy rainfall. Removal vegetation cover for different land use like railway lines, roads, buildings, or even agriculture has caused Sheet, Rill or Gully erosion
* Shifting cultivation – heavy rains wash away the bare soil from the slopes to the valleys below.
* Uncontrolled grazing of domestic animals in the valleys and the upper slopes.
CAUSES OF SOIL EROSION IN INDIA
1) Heavy population pressure on land: – forest cover as low as 20.55% of total area – population continues to rise at a rapid rate – more forests are destroyed – heavy pressure on land.
2) Nature of Rainfall: receives 80 to 90 per cent of rainfall in the monsoon season. – Heavy downpour during monsoon months causes floods. – Remaining months – droughts – these affect soils
3) Overgrazing – number of domestic animals, especially cattle highest in world – cattle freely graze in open lands making them bare of vegetation-winds carry away dry soil particles – Rajasthan
4). Bad farming techniques – plough fields in traditional ways – small size of holdings, absence of terracing, contour cultivation, crop rotation, improper use of manure have caused erosion
5) Topography – North –Eastern parts of India, Shiwaliks and the hilly regions in south India are affected by soil erosion because of steep slopes and heavy rainfall. During heavy rainfall, soils are washed away by running water down the slope.
6) Deforestation: destruction of forests for cultivation – cutting of trees exposes the soil to water and wind which leads to soil erosion
REGIONS OF SOIL EROSION
*Rajasthan, Madhya Pradesh, Maharashtra, UP, Gujarat, Andhra Pradesh, Karnataka. Worst affected areas include:
* The badlands of Chambal and Yamuna rivers
* The piedmont zone of the western Himalayas
* The Chhota Nagpur plateau region
* The Tapi-Sabarmati valley region in Gujarat
* The regur soil area of Maharashtra
* The dry areas of Rajasthan, Gujarat and Haryana
EFFECTS OF SOIL EROSION:
* Loss of fertile top soil
* Lowering of the underground water table and decreasing soil moisture
* Drying of vegetation and extension of arid lands, increase in the frequency of droughts and floods
* Silting of river and canal beds, Recurrence of landslides, adverse effect on economic prosperity and cultural development
* Wind erosion reduces the productive capacity of soil, as most of the nutrients required by the plants are carried by the wind.
PREVENTION OF SOIL EROSION AND SOIL CONSERVATION
1. Terrace Farming: On hilly slopes, terraces act as bunds and prevent the soil from being washed away.
2. Contour Farming: Farming along contours on a slope prevents soil being washed away by rainwater or by surface run off. Contours act like bunds. Terraces are leveled into step like small fields with even slope.
3)Afforestation: Planting of trees along the edges of the fields, the waste land and on steep slopes to prevent soil erosion as well as to enhance the capacity of the soil to retain water, and to increase area under forests and to stop the indiscriminate felling of trees.
4) Shelter Belts: Farmers plant trees in several rows to check wind erosion. Known as wind breaks.
5) Strip cropping: Crops are grown in alternate strips of land to check the impact of the winds.
6) Construction of dams: Rivers cause soil erosion. Dams are built-in the upper course of rivers to control erosion of soil. This would check the speed of water and thereby save soil from erosion
7) Ploughing Gullies: The gullies made in the soil are plugged with deposition of silt during heavy rains.
8) Shifting or Jhuming or slash and burn type of agriculture should be banned.
SOIL CONSERVATION SCHEMES
1. The centrally sponsored scheme of Integrated Watershed Management in the catchments of flood-prone rivers was launched during sixth Plan in eight flood-prone rivers of the Gangetic Basin covering seven States and one Union Territory. It aims at enhancing the ability of the catchment by absorbing larger quantity of rainwater, reducing erosion and consequent silt load in the stream and river beds and thus helping to mitigate the fury of floods in the productive plains.
2. A scheme for reclamation and development of ravine areas was launched in 1987-88 in MP, UP and Rajasthan. – included peripheral bunding to halt further ingress of ravines, afforestation of ravines, afforestation of ravines for fuel, fodder and reclamation of shallow ravines.
3. Control of shifting cultivation is implemented since 1994-95 in the States of Arunachal Pradesh, Assam, Manipur, Meghalaya, Nagaland, and Tripura. The integrated programme envisages settling of families practicing shifting cultivation. It helps them to practice terraced cultivation, raising of horticultural plantations and afforestation to support animal husbandry and to meet fuel and fodder requirements.
4. In urban areas, rain water harvesting is means of checking soil erosion, besides recharging ground water.
Other Soils: The other soils in the category of the Indian soils are as follows:
These soils cover 2 lakh sq. km areas in dry areas of Rajasthan, Gujarat, Punjab, and Haryana. These coarse soils are suitable for cultivation of jowar, bajara, cotton etc.
Saline and Alkaline Soils: These soils are found in the dry and marshy areas. These are locally known as Bhur, Rehu, Kallar. The accumulation of salts makes these soils infertile.
Mountain soils are found in, as the name suggests, in mountainous regions. They are quite prone to soil erosion as a result of the top soil getting washed away due to the steep slopes of the mountains after a period of heavy rainfall.
These soils are mostly thin and infertile. These include peat, meadow and forest hill soils.
The major characteristics of this soil are:
*they are rich in humus
* are coarse and infertile. They are deficient in potash, phosphorous and lime.
*Tea, coffee, spices and tropical fruits
The states of Jammu and Kashmir, Himachal Pradesh and Uttaranchal, Assam, Sikkim as well as higher reaches of Arunachal Pradesh have mountain soil.
ARID AND DESERT SOILS
Large part of arid and semi-arid region of Rajasthan and adjoining areas of Punjab and Haryana
Desert soils are found in arid regions which receive very little rainfall.
*Low rainfall and high temperature are reasons for the formation of this soil .
*Having less than 50 cm rainfall . The high temperature adds to the loss of any remaining moisture in the soil. The soil is therefore sandy in nature. Thar Desert in Rajasthan has sandy soil.
*Covers an area of about 1.4 lakh sq km
* Originated from the mechanical disintegration of the ground rock of by deposition by wind
* Desert soil contain 90% of sand and 5% of clay. It contains rich percentage of soluble salts, but lack in organic matter.
* Are porous and coarse .
* They respond well to irrigation and manuring , especially phosphate and nitrate.- it can improve the soil fertility as it is seen in the case of Indira Gandhi Canal in Rajasthan.
* Only suitable for drought resistance crops like millets, barley, cotton, maize and pulses.
SALINE AND ALKALINE SOILS
Soils with high proportion of salts and alkalis are called saline and alkaline soils .
They are formed due to accumulation of tidal water in adjoining coasts where drainage is poor. They are found in drier parts of Bihar, Rajasthan, U.P., Punjab, Haryana, Maharashtra. These soils contain many salts like sodium, magnesium and calcium which make them infertile and render unfit for agriculture.
Found in continuously water-logged areas, or marshy areas especially in the coastal regions near the sea or near the deltas.
* It covers about 56,000 sq km.
* They are formed as a result of water-logging
* It contain iron and varying amount of decayed organic matter.
* Found in southern parts of Shiwaliks, Jammu and Kashmir, U.P.
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NOTES – Soils of India and Soil Conservation
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