Overview
Soil is the thin living skin of the earth on which every crop, every forest and every grassland stands. India, with its great range of rocks, relief, climate and vegetation, has an equally great range of soils: the deep black cotton soil of the Deccan lavas, the fertile alluvium of the Ganga plain and the Bengal delta, the red soils of the peninsular granites, the laterites of the wet plateaus and the sandy soils of the Thar. This section of the Class 10 Geography course explains what soil is and how it forms, the factors that control its character, the profile of horizons in a mature soil, and the classification of Indian soils into the eight groups recognised by the Indian Council of Agricultural Research: alluvial, black, red, laterite, desert, mountain, saline and peaty soils. For each it gives the distribution, the characteristics, the crops and the problems. It then turns to the soils of West Bengal, from the tea soils of Darjeeling to the mangrove mud of the Sundarbans, and closes with soil erosion, its causes and forms, the regions of India most affected, and the measures of soil conservation, from contour ploughing to afforestation. The chapter matters because soil is a resource that takes centuries to form and a season to lose, and because Madhyamik asks for soil types, their distribution and conservation every year, including map-pointing of the black and laterite soil regions.
Learning Objectives
- Define soil and explain the process and factors of soil formation.
- Describe the soil profile and the characteristics of the A, B and C horizons.
- Classify the soils of India into the eight major groups and locate each on a map.
- Describe the characteristics, distribution and crops of alluvial, black, red and laterite soils.
- Compare bhangar and khadar, and explain why black soil is suited to cotton.
- Describe the soils of West Bengal region by region.
- Explain the causes and types of soil erosion and identify the erosion-prone regions of India.
- Describe the methods of soil conservation and explain why conservation is necessary.
Topics in this chapter
14 topics · tap a topic title to jump straight to it.
What soil is and how it forms
Soil is the loose, uppermost layer of the earth's crust, made of weathered rock particles mixed with decayed organic matter, water and air, in which plants grow. The scientific study of soil is pedology, and the process of soil formation is pedogenesis. Soil is a natural resource of a special kind: it is renewable in principle, since it is constantly being formed, but so slowly that for practical purposes it must be treated as non-renewable. It takes 200 to 1,000 years to form 2.5 cm of topsoil, and a single monsoon can strip that much from a bare hillside.
Soil forms in two stages. The first is weathering, the breaking down of the parent rock into small particles by physical, chemical and biological agents. Heating and cooling crack the rock, frost wedges it apart, water dissolves its soluble minerals, oxygen rusts its iron, plant roots and burrowing animals split it further. The result is a layer of loose mineral fragments called the regolith. The second stage is the addition of humus, the dark, decayed remains of plants and animals broken down by bacteria and fungi. Humus binds the mineral particles, holds water and supplies nitrogen and other nutrients; it is what turns regolith into soil. Rainwater percolating through the soil dissolves the soluble substances and carries them downward, a process called leaching; where it is strong, as in the wet tropics, the upper soil is left poor in plant food.
Soil is made of four parts. The mineral matter, about 45 per cent, consists of particles of sand (coarse, 0.05-2 mm), silt (fine, 0.002-0.05 mm) and clay (very fine, below 0.002 mm); the proportions decide the texture. A soil with a balanced mixture of the three is a loam, the ideal farm soil. Organic matter, 5 per cent, is the humus. Water and air, about 25 per cent each, fill the pore spaces between the particles. Soil also contains the living population of bacteria, fungi, earthworms and insects that keep it fertile.
The fertility of a soil is its ability to supply the nutrients a plant needs, chiefly nitrogen, phosphorus and potassium (N, P, K) and smaller quantities of calcium, magnesium, sulphur and iron; its productivity is the yield it actually gives, which depends also on water, drainage and management.
- On a granite hillside in Chhotanagpur the rock weathers into a red gritty regolith; the sal forest above it drops leaves that decay into humus and, over centuries, a red loamy soil forms.
- A jar of garden soil shaken with water and left to settle shows sand at the bottom, silt above it, clay at the top and humus floating: a simple demonstration of the four components.
- A soil with 40 per cent sand, 40 per cent silt and 20 per cent clay is a loam; the Ganga delta soils near Kolkata are silty clay loams.
- Soil = weathered rock particles + humus + water + air; roughly 45 per cent minerals, 5 per cent organic matter, 25 per cent water, 25 per cent air.
- Texture by particle size: sand 0.05-2 mm; silt 0.002-0.05 mm; clay below 0.002 mm; loam = balanced mixture.
- Pedology = the study of soil; pedogenesis = soil formation; leaching = downward removal of soluble matter by percolating water.
Factors of soil formation
Five factors act together to decide what kind of soil forms at a place. The first is the parent rock. The mineral part of the soil is inherited from the rock beneath it or from the material deposited on it. Basalt lava weathers into black soil rich in iron, magnesium and lime; granite and gneiss weather into red or yellow sandy soils rich in iron but poor in lime; sandstone gives sandy soil; shale gives clay; and river silt gives alluvium. In the peninsula, where the soils lie on the rocks that produced them, they are called sedentary or residual soils; in the plains, where the material was carried from elsewhere by rivers, wind or glaciers, they are transported soils.
The second factor is climate, which most geographers consider the most important, because soils of the same climate are similar even on different rocks. Temperature decides the rate of chemical weathering and of the decay of humus: in hot wet regions weathering is deep but humus is destroyed quickly, so the soil is deep but poor. Rainfall decides leaching: heavy rain washes out lime, potash and silica and leaves iron and aluminium, giving laterite; low rainfall leaves the salts in the soil and gives the alkaline soils of dry regions. The third factor is relief: on steep slopes the soil is thin because it is washed away as fast as it forms, while in valleys and plains it accumulates deeply; slope also governs drainage, and waterlogged hollows produce peaty soils.
The fourth factor is natural vegetation and the living organisms of the soil. Forests and grasses supply the leaf litter that becomes humus, and their roots bind the soil; the soil under grassland is richer in humus than under forest because grass roots die every year. Bacteria fix nitrogen, and earthworms mix and aerate the soil. The fifth factor is time: a young soil on a fresh flood deposit has no horizons and much unweathered material; a mature soil that has lain undisturbed for thousands of years has a full profile. Human action is sometimes counted as a sixth factor, since ploughing, manuring, irrigation and deforestation alter soils faster than any natural process.
- The Deccan lava between Nagpur and Pune weathers into black regur in a climate of 60-100 cm of rain; the same rock under 250 cm of rain on the crest of the Western Ghats weathers into laterite. Climate overrides the parent rock.
- Along a slope in Purulia the ridge crest has 10 cm of gravelly soil, the middle slope 40 cm of red loam and the valley floor 1.5 m of dark clay: relief controls depth.
- The Ganga alluvium near Patna is a transported soil, brought as silt from the Himalaya; the red soil of Bankura is sedentary, formed from the gneiss beneath it.
- Factors of soil formation: parent rock, climate, relief, vegetation and organisms, time (and human action).
- Sedentary (residual) soil = formed in place on its parent rock; transported soil = carried from elsewhere by water, wind or ice.
The soil profile and its horizons
If a pit is dug in a mature soil down to the rock, the wall of the pit shows a series of layers that differ in colour, texture and composition. This vertical section is the soil profile, and each layer is a horizon. The profile is the record of how the soil formed, and its study tells the farmer how deep the roots can go, where the water table lies and which layer holds the plant food.
At the top lies a thin layer of undecayed and partly decayed leaves, twigs and grass, the O horizon or litter layer, present under forest and grassland but absent from ploughed fields. Below it is the A horizon, the topsoil. It is the darkest layer because it is richest in humus, it is the most weathered, it holds most of the roots, the earthworms and the bacteria, and it is the layer from which water percolating downward removes the soluble minerals and the finest clay. It is therefore also called the zone of eluviation or washing out. Its depth varies from a few centimetres on a hillside to a metre in a flood plain, and it is the part of the soil that erosion removes first.
Below the topsoil is the B horizon, the subsoil. It is lighter in colour, has less humus and fewer roots, and receives the clay, iron, aluminium and lime washed down from the A horizon; it is the zone of illuviation or washing in. In dry climates lime accumulates here as a hard layer called kankar, common in the older alluvium of the Ganga plain; in wet climates iron accumulates and may harden into a laterite crust. The A and B horizons together are called the solum, the true soil.
Beneath the subsoil is the C horizon, the weathered and broken parent material or regolith, partly decomposed rock that has not yet become soil, and below that the R horizon, the unaltered bed rock. In young soils, such as the fresh silt of a river bank, the horizons have not yet developed and the profile is a single uniform layer; in old soils on the peninsular plateau the profile may be several metres deep with every horizon clearly marked.
- A road cutting in the Bardhaman laterite belt shows 20 cm of grey topsoil, 60 cm of mottled red and yellow subsoil with iron nodules, and then the soft white weathered gneiss: A, B and C horizons.
- In the bhangar of western Uttar Pradesh a pit shows a lime-rich layer of kankar nodules at about 1 m depth: the B horizon of a dry-climate soil.
- A fresh char in the Ganga near Malda, deposited last monsoon, is uniform grey silt from top to bottom with no horizons: a soil with no time yet to form a profile.
- Soil profile: O (litter) → A (topsoil, humus-rich, zone of eluviation) → B (subsoil, zone of illuviation) → C (weathered parent material, regolith) → R (bed rock).
- Solum = A + B horizons = the true soil.
Classification of Indian soils
India's soils have been classified in several ways. The oldest is the classification of the ancient texts into urvara (fertile) and usara (sterile), and every region has its own farmers' names: regur for the black soil, bhangar and khadar for the old and new alluvium, bhur for sandy river banks, reh and kallar for salty patches. The modern classification is based on the work of the Indian Council of Agricultural Research (ICAR), which in 1956 grouped the soils of the country by their origin, colour, composition and location into eight major groups: alluvial soils, black soils, red and yellow soils, laterite soils, arid or desert soils, mountain or forest soils, saline and alkaline soils, and peaty and marshy soils. The National Bureau of Soil Survey has since refined this into the international system of soil orders, but the ICAR groups are the ones the school course follows.
Two broad divisions underlie the eight groups. The soils of the northern plains and the coastal strips are transported, laid down by rivers, and are deep, fine-textured and rich because the rivers bring fresh silt every year. The soils of the peninsular plateau are mostly sedentary, formed in place on the ancient crystalline rocks and the Deccan lavas, and their character follows the rock: black on basalt, red on granite and gneiss, laterite where rainfall is heavy enough to leach them.
By area, the alluvial soils are the largest group, covering about 43 per cent of the country or 143 million hectares, and they support the densest population. Black soils cover about 15 per cent, chiefly in the Deccan; red and yellow soils about 18 per cent, in the eastern and southern peninsula; laterites about 3.7 per cent; desert soils about 4.5 per cent in the north-west; mountain soils in the Himalayan belt; and the saline and peaty soils occur in small scattered patches. Each group is described in turn in the topics that follow, always under the same four heads the examination expects: formation, distribution, characteristics and crops.
- A map-pointing question asks for 'a region of black soil': the answer is the Deccan lava plateau of Maharashtra around Nagpur or Pune.
- A question asking for 'the soil type covering the largest area in India' is answered by alluvial soil, about 43 per cent of the country.
- The soil of the Kolkata region is transported alluvium; the soil of Bankura is sedentary red soil on gneiss: two groups within one state.
- ICAR (1956) classification: 1 alluvial, 2 black, 3 red and yellow, 4 laterite, 5 arid/desert, 6 mountain/forest, 7 saline/alkaline, 8 peaty/marshy soils.
- Approximate share of India's area: alluvial 43 per cent, red and yellow 18 per cent, black 15 per cent, desert 4.5 per cent, laterite 3.7 per cent.
Alluvial soils: bhangar and khadar
Alluvial soil is the soil deposited by rivers. It is the most widespread and the most important soil of India, covering the whole of the northern plain from Punjab to Assam, the deltas of the Mahanadi, Godavari, Krishna and Kaveri, and narrow strips along the east and west coasts. It is a transported soil, made of the silt, sand and clay that the Himalayan and peninsular rivers have carried down over thousands of years and spread across their flood plains; in the Ganga-Brahmaputra plain the alluvium is several hundred metres deep.
The alluvium of the plains is divided by age into two types. Khadar is the new alluvium of the present flood plain, renewed by fresh silt every year when the river overflows. It is light in colour, sandy to loamy, porous, free of stones and very fertile, and it lies in the low ground along the rivers. Bhangar is the old alluvium of the higher terraces, above the level of the floods, laid down in an earlier period and not renewed. It is darker, more clayey, and often contains nodules of impure calcium carbonate called kankar; it is less fertile than khadar but still good farm land. In the delta of Bengal the alluvium is finer and more clayey; in the Punjab it is coarser and sandy; along the foot of the Shiwaliks the coarse gravelly deposits are called bhabar, and the marshy belt below them the terai.
The characteristics of alluvial soil are its depth, its fine texture varying from sandy loam to clay, its richness in potash, phosphoric acid and lime and its poverty in nitrogen and humus, which is why manure and nitrogenous fertiliser are so heavily used in the plains. It is easy to plough, retains moisture well and responds to irrigation. Its colour ranges from light grey to ash grey.
Alluvial soil is the soil of India's granary. Wheat, rice, sugarcane, maize, oilseeds, pulses, jute in Bengal and cotton in Punjab all grow on it, and it supports the densest rural population in the country, with Uttar Pradesh, Bihar, West Bengal and Punjab as its heartland. Its problems are waterlogging and salinity where irrigation is careless, the exhaustion of nutrients under intensive cropping, and river erosion of the khadar.
- The khadar along the Bhagirathi in Murshidabad is renewed every monsoon and grows jute and aus rice; the bhangar of the Barind tract in Malda, above the floods, is older, harder and grows a single crop of aman rice.
- The Ganga plain at Kanpur has alluvium more than 1,000 m deep, drilled through by tube-wells without touching rock.
- Punjab's alluvium, being sandy loam and irrigated, gives the highest wheat yield in India, about 5 tonnes per hectare.
- Alluvial soil: transported by rivers; rich in potash, phosphoric acid and lime; poor in nitrogen and humus; covers about 43 per cent of India.
- Khadar = new alluvium of the flood plain, renewed yearly, light and sandy, most fertile; Bhangar = old alluvium of the terraces, clayey, with kankar, not renewed.
- Bhabar = coarse gravelly deposit at the foot of the Shiwaliks; Terai = marshy belt below the bhabar.
Black soil (regur)
Black soil is the soil of the Deccan lava plateau. It is formed in place by the weathering of the basalt that poured out of fissures in the Cretaceous period and covered the north-western peninsula, and it inherits from that rock its high content of iron, magnesium, lime and alumina. Its black colour comes from the titanium and iron compounds and from the humus it holds. It is known as regur, from the Telugu word for black, and as black cotton soil because cotton is the crop it suits best.
Black soil covers about 5.5 lakh sq km, the whole of the Deccan trap area: most of Maharashtra, the Malwa plateau of Madhya Pradesh, the Saurashtra and Kathiawar parts of Gujarat, the northern districts of Karnataka, western Telangana and the Rayalaseema region of Andhra Pradesh, and small patches in Tamil Nadu. It is deepest on the plains of the Tapti, Narmada, Godavari and Krishna, where it may reach 3 m, and thin on the uplands.
Its characteristics are distinctive. It is very clayey, with 40-60 per cent clay, and therefore has a very high moisture-holding capacity; it absorbs the monsoon rain and holds it through the dry season, so that crops can be grown without irrigation. It swells when wet, becoming so sticky that it cannot be ploughed, and shrinks when dry, developing deep, wide cracks through which air enters and the lower soil is turned over, a process called self-ploughing. It is rich in lime, iron, magnesia, potash and alumina but poor in nitrogen, phosphorus and organic matter. It is slightly alkaline and not leached, because rainfall is moderate.
The great crop of the black soil is cotton: the deep soil holds moisture for the long growing season and the lime and potash suit the plant, which is why Maharashtra and Gujarat are India's leading cotton states. Jowar, wheat, sugarcane, groundnut, soyabean, oranges around Nagpur, tobacco in Guntur and linseed also grow on it. Its problems are the difficulty of tillage when wet, water-logging in flat areas, and the sheet erosion of the thinner soils on slopes.
- The cotton belt of Vidarbha (Nagpur, Amravati, Akola, Yavatmal) lies wholly on regur, and cotton is grown as a rain-fed kharif crop in only 70-90 cm of rain because the soil stores the water.
- In May the fields near Solapur show cracks 10 cm wide and a metre deep; after the first rain the soil swells and the cracks close within a week.
- Black soil of the Narmada valley near Hoshangabad is more than 3 m deep and grows wheat and soyabean in rotation.
- Black soil (regur): formed from Deccan basalt; 40-60 per cent clay; rich in lime, iron, magnesia, potash; poor in nitrogen, phosphorus, humus; swells when wet, cracks when dry (self-ploughing).
- Distribution: Maharashtra, Malwa (MP), Saurashtra (Gujarat), north Karnataka, western Telangana and Andhra Pradesh; about 15 per cent of India.
Red and yellow soils
Red soil is the second most extensive soil of India, covering about 18 per cent of the country. It is a sedentary soil formed in place by the weathering of the ancient crystalline and metamorphic rocks of the peninsula, the granites, gneisses and schists of the Archaean shield, under a climate of moderate rainfall. Its red colour comes from the wide diffusion of iron oxide (ferric oxide) through the soil; where the soil is water-logged and the iron is in the hydrated form the colour is yellow, which is why the group is called red and yellow soils.
Red soil surrounds the black soil region on the east and south and occupies most of the eastern and southern peninsula: Tamil Nadu, southern Karnataka, the interior of Andhra Pradesh and Telangana, the Chhotanagpur plateau of Jharkhand, most of Odisha and Chhattisgarh, eastern Madhya Pradesh, the southern parts of West Bengal (Purulia, Bankura, Birbhum, western Bardhaman and Paschim Medinipur), parts of Meghalaya and the Bundelkhand region of Uttar Pradesh. It is thin and gravelly on the uplands and deeper, darker and more fertile in the valleys.
Its characteristics are these. It is generally light-textured, sandy to loamy, porous and friable, so it drains quickly and does not retain moisture well, which makes irrigation necessary for a second crop. It is poor in nitrogen, phosphorus, humus and lime, though fairly rich in potash and iron, and is slightly acidic. It is easy to plough, and when manured and irrigated it responds well. Its chemical poverty makes it less fertile than the alluvial and black soils, and on the plateau of Purulia or Rayalaseema it supports only a single rain-fed crop of coarse grain.
The crops of the red soil are the hardy ones: ragi, bajra, jowar, groundnut, pulses, potato and tobacco, with rice in the irrigated valleys and tank-fed lowlands of Tamil Nadu and Karnataka, and coffee, tea and rubber where rainfall is heavy. Wheat is grown on it in Bundelkhand and Chhattisgarh. Its problems are gully erosion, especially in the ravines of Bundelkhand, low fertility and drought, since it dries out fast.
- The tank-irrigated rice fields of Tamil Nadu and the dry ragi fields of southern Karnataka both lie on red soil; the difference is water, not soil.
- The laterite-red upland of Bankura yields 1.5 tonnes of rain-fed rice per hectare against 3 tonnes on the alluvium of Hooghly 100 km east.
- Groundnut, which needs a loose, well-drained soil for its pods to form underground, is the main cash crop of the red soil belt of Anantapur and Chittoor.
- Red soil: sedentary, from granite and gneiss; red from ferric oxide, yellow where hydrated; light-textured, porous; poor in nitrogen, phosphorus, humus, lime; fairly rich in potash and iron; slightly acidic.
- Distribution: Tamil Nadu, southern Karnataka, Andhra Pradesh, Telangana, Chhattisgarh, Odisha, Jharkhand, south-western West Bengal, Bundelkhand; about 18 per cent of India.
Laterite soils
Laterite takes its name from the Latin later, a brick, because the soil can be cut into blocks that harden in the sun and are used as bricks in Kerala and Karnataka. It is a soil of the humid tropics, formed under the conditions of high temperature and heavy rainfall with alternating wet and dry seasons. The heavy rain leaches the silica, lime, potash and other soluble matter downward and out of the soil, and the dry season draws the water back up by capillary action, leaving behind a concentration of the insoluble oxides of iron and aluminium at and near the surface. The result is a reddish, porous, nodular soil, hard as brick when it dries.
Laterite is found wherever the rainfall exceeds about 200 cm on old crystalline or lava plateaus with a dry season: the crests and western slopes of the Western Ghats in Maharashtra, Goa, Karnataka and Kerala, the Nilgiri and Cardamom hills, the eastern margin of the Chhotanagpur plateau in Jharkhand, the Rajmahal hills, the Odisha uplands, the hills of Meghalaya and Assam, and the western fringe of West Bengal in Birbhum, Bankura, Bardhaman and Paschim Medinipur, the rarh region. About 3.7 per cent of India is laterite.
Its characteristics are its red colour and hardness, its coarse, gravelly texture with iron nodules, its poverty in nitrogen, phosphorus, potash, lime and humus, since these have all been leached, and its acidity. Bacteria that would form humus are destroyed by the high temperature, so organic matter is low. It is well drained but cannot hold water. It is, in short, one of the least fertile soils of India, and much of the laterite country is barren scrub, badland or sal forest.
Yet laterite is useful. With heavy manuring and lime it grows cashew, tapioca, coconut, rubber, coffee, tea and pineapple on the wet western slopes, and rice in the lowlands where the softer, moister laterite is mixed with alluvium. Cashew is the characteristic crop of the laterite coast of Kerala, Karnataka and Goa. Laterite blocks are the building stone of Malabar, and the laterite of Odisha and Jharkhand contains the bauxite from which aluminium is made. Its problems are erosion, especially the gullying of the Bengal and Jharkhand laterites into badlands, and low fertility.
- The Garhbeta badlands of Paschim Medinipur ('Gongoni') are a laterite plateau cut by gullies into a red miniature canyon: leaching and erosion together.
- The cashew orchards of the Kerala coast and the Konkan stand on hard laterite that will grow little else without manure.
- Houses across Malabar and Goa are built of red laterite blocks cut soft from the quarry and hardened in the sun, the origin of the name.
- Laterite: formed by leaching under heavy rain and high temperature with alternate wet and dry seasons; rich in iron and aluminium oxides; poor in nitrogen, phosphorus, potash, lime and humus; acidic; hardens like brick on drying.
- Distribution: Western Ghats, Nilgiri, Chhotanagpur margin, Rajmahal, Odisha uplands, Meghalaya, rarh region of West Bengal; about 3.7 per cent of India.
Desert soil, mountain soil, saline and peaty soils
Desert or arid soil covers the Thar of western Rajasthan and extends into Haryana, southern Punjab, Kutch and northern Gujarat, about 4.5 per cent of India. It is formed by the mechanical weathering of rocks in a dry climate and by the deposit of wind-blown sand from the Indus valley and the sea coast. It is sandy, 90 per cent sand, light red to brown in colour, porous and very low in humus and moisture. Because rainfall is under 25 cm and evaporation is high, the salts are not leached but accumulate; the soil is alkaline and often has a layer of kankar or gypsum at depth. It is rich in soluble salts and phosphate but poor in nitrogen. It is fertile when watered, as the Indira Gandhi canal has shown around Bikaner and Sri Ganganagar, where wheat, cotton and mustard now grow on land that grew only bajra and moth.
Mountain or forest soil is found on the slopes of the Himalaya from Jammu and Kashmir to Arunachal Pradesh, including the Darjeeling hills, and in the higher parts of the Western and Eastern Ghats. It is thin, stony, immature, with an undeveloped profile because slopes are steep and erosion is constant. Its character changes with height and vegetation: under the sub-tropical forests of the lower slopes it is loamy and rich in humus but acidic, in the valleys it is deep and fertile, and above the tree line it is a thin, raw skeletal soil. Where rainfall is heavy it is leached and podzolic. It supports tea in Darjeeling and Assam, apples and other temperate fruit in Kashmir and Himachal, potatoes, maize and rice on terraces, and spices in the Western Ghats.
Saline and alkaline soils, called usar, reh, kallar or thur in different regions, occur in patches in the dry plains of Uttar Pradesh, Haryana, Punjab, Rajasthan, Gujarat and Maharashtra, and in the coastal deltas including the Sundarbans. They form where evaporation exceeds rainfall and the ground water is near the surface, so that dissolved sodium, magnesium and calcium salts rise by capillary action and are left as a white crust when the water evaporates; careless canal irrigation without drainage has created millions of hectares of such land in the Punjab and western Uttar Pradesh. They are infertile until the salts are washed out by good drainage and gypsum is added. Salt-tolerant crops such as barley, rice and the leguminous dhaincha are grown in reclamation.
Peaty and marshy soils form in areas of heavy rainfall and high humidity where drainage is poor, so that dead vegetation accumulates faster than it decays. They are black, heavy, acidic, and very rich in organic matter, sometimes 40 per cent. They occur in the Kottayam and Alappuzha districts of Kerala (the kari lands), the Sundarbans and other parts of coastal West Bengal, coastal Odisha, the Tarai of north Bengal and Uttar Pradesh, and the Almora district of Uttarakhand. They grow rice when drained.
- Sri Ganganagar in Rajasthan, on desert soil, is now called the granary of the state because the Indira Gandhi canal made its sandy but salt-rich soil grow wheat and cotton.
- In parts of Etawah and Mainpuri in Uttar Pradesh a white crust of reh covers fields ruined by canal seepage; the government reclaims them with drainage and gypsum.
- The kari lands of Kuttanad in Kerala are peaty rice fields below sea level, black with organic matter and protected by bunds.
- Desert soil: sandy, alkaline, salt-rich, poor in nitrogen and humus; western Rajasthan, Kutch, Haryana; fertile under irrigation.
- Mountain soil: thin, stony, immature, humus-rich under forest, acidic; Himalaya and higher Ghats; tea, fruit, potatoes.
- Saline soil (usar, reh, kallar): salts rise by capillary action where evaporation exceeds rainfall; reclaimed by drainage and gypsum.
- Peaty soil: black, acidic, up to 40 per cent organic matter, in waterlogged humid areas; Kerala kari lands, Sundarbans, Tarai.
Soils of West Bengal
West Bengal contains five of India's soil groups, arranged in belts that follow the relief from the Himalaya to the sea. In the Darjeeling hills the soil is mountain soil: thin, brown, stony, acidic and rich in humus under the forest and the tea gardens, deeper in the valleys. Tea grows best on the well-drained, acidic, humus-rich loam of the slopes between 1,000 and 2,000 m.
At the foot of the hills the Terai and Duars of Darjeeling, Jalpaiguri and Alipurduar have coarse, gravelly, porous soils near the hills, becoming a heavy, dark, waterlogged, peaty loam farther out; they are acidic, rich in organic matter, and grow tea in the Duars and rice, jute and pineapple elsewhere. The Barind tract of Malda, Uttar and Dakshin Dinajpur is old alluvium (bhangar), grey to reddish, clayey, with kankar, hard when dry, and grows a single rain-fed aman rice crop and mango in Malda.
The Ganga plain and delta, from Murshidabad, Nadia and Bardhaman to Hooghly, Howrah, Kolkata and the 24 Parganas, has new alluvial soil (khadar), grey, silty to clayey loam, neutral, renewed by floods, poor in nitrogen but rich in potash and lime. It is the most fertile soil of the state and grows rice, jute, potato, sugarcane, mustard and vegetables, with two or three crops a year under irrigation. The moribund delta of Nadia and Murshidabad, where the distributaries have silted, has a heavier clay than the active delta.
The Rarh region in the west, Purulia, Bankura, Birbhum, western Bardhaman and Paschim Medinipur, is the eastern edge of the Chhotanagpur plateau and has red and laterite soils: red, gravelly, acidic, poor in nitrogen, phosphorus and humus, hardening in the dry season and gullied in the laterite belt. It supports rain-fed aman rice in the valleys, sal forest on the uplands, and needs tanks and manure for any second crop.
The Sundarbans and the coast of Purba Medinipur have saline and marshy soils: grey to black clay, waterlogged, tidal, with salt in the profile, growing mangrove forest and salt-tolerant rice behind embankments. The problems of the state's soils are erosion of the laterite belt, salinity and cyclone flooding in the Sundarbans, waterlogging in the Terai, and the depletion of nitrogen by intensive rice cropping in the delta, which makes West Bengal one of the largest users of fertiliser per hectare in India.
- The tea gardens of Darjeeling at 1,200-2,000 m stand on acidic mountain loam with a pH of about 5, which the tea bush needs.
- Hooghly district grows three crops a year, aus, aman and potato, on the same khadar field, while Purulia grows one crop of aman on its red soil.
- After cyclone Aila in 2009 salt water stood on the fields of the Sundarbans for months and rice would not grow for two seasons until the salt was washed out.
- West Bengal soil belts from north to south: mountain soil (Darjeeling) → Terai/Duars (coarse to peaty) → Barind old alluvium (bhangar) → Ganga delta new alluvium (khadar) → Sundarbans saline/marshy; and in the west, red and laterite soils of the Rarh.
- Rarh region = Purulia, Bankura, Birbhum, western Bardhaman, Paschim Medinipur: red and laterite soil.
Soil erosion: meaning and causes
Soil erosion is the removal of the topsoil by running water, wind, glaciers, waves or gravity at a rate faster than it can be formed. Soil is always being moved a little, and a slow natural erosion balanced by soil formation is part of the working of the landscape. It becomes a problem when the balance is broken, and in India it has been broken over about 130 million hectares, more than a third of the country, which lose an estimated 5,300 million tonnes of soil every year. Because the topsoil is the layer that holds the humus and the plant food, its loss lowers the yield of every crop, silts the rivers and reservoirs, and turns good land into gullied waste.
The causes are partly natural and mostly human. The natural causes are the torrential character of the monsoon rain, which falls in heavy bursts on bare fields at the end of the dry season; the steep slopes of the Himalaya and the Ghats; the loose nature of the alluvium and the sandy soils; the strong winds of the dry north-west; and the shifting of the rivers of the plains, which undercut their banks.
The human causes make these worse. Deforestation removes the cover of leaves that breaks the force of the rain and the roots that bind the soil; the hills of the Himalaya, the Chhotanagpur plateau and the Western Ghats have all been stripped for timber, fuel and farm land. Overgrazing by India's vast herds of cattle, goats and sheep leaves the grasslands bare, especially in the dry regions of Rajasthan and the Deccan. Shifting cultivation (jhum) in the north-eastern hills clears and burns the forest on steep slopes and abandons the plot after two years. Faulty farming methods such as ploughing up and down the slope, leaving fields fallow and bare through the pre-monsoon storms, growing the same crop year after year and over-irrigating all loosen or expose the soil. Mining, quarrying, road building and construction lay bare large areas, as in the coal belt of Jharkhand and Raniganj. And the pressure of population pushes cultivation onto steeper and drier land that should have been left under grass or forest.
- The Shiwalik hills of Punjab and Haryana, deforested and overgrazed, send seasonal torrents called chos down onto the plain, burying fields under sand.
- In the jhum areas of Nagaland and Mizoram a slope cleared and burned in February loses 30-40 tonnes of soil per hectare in the first monsoon.
- The Raniganj coalfield's open-cast mines have left thousands of hectares of overburden dumps that erode into the Damodar every monsoon.
- Soil erosion = removal of topsoil by water, wind, ice or gravity faster than it is formed.
- About 130 million hectares of India are affected by erosion, losing about 5,300 million tonnes of soil a year.
- Causes: natural (torrential rain, steep slopes, loose soil, strong wind) and human (deforestation, overgrazing, shifting cultivation, faulty farming, mining and construction).
Types of soil erosion and the regions affected
Erosion by running water is the most widespread in India and takes three forms in succession. Sheet erosion is the removal of a thin, almost uniform layer of topsoil from a whole slope by rain wash; it is the hardest to notice, because the field looks unchanged, but it is the most damaging over large areas, and it shows itself in the gradual paling of the soil as the dark humus layer is removed. Rill erosion follows when the running water gathers into small channels a few centimetres deep, which the plough can still erase. Gully erosion is the third stage: the rills deepen and widen into gullies too large to plough across, which grow headward into the field every monsoon and cut the land into steep-sided ravines. Once gullied, land is lost to farming; the Chambal ravines of Madhya Pradesh, Rajasthan and Uttar Pradesh, the badlands of the Yamuna and the laterite gullies of Birbhum, Bankura and Paschim Medinipur in West Bengal are all examples. Stream-bank erosion is a fourth form: rivers undercut their banks at every bend and swallow fields and villages, as the Ganga does in Malda and Murshidabad and the Brahmaputra in Assam.
Wind erosion removes the fine particles from bare, dry, sandy soil and carries them away as dust or piles them as dunes, leaving coarse sand behind. It is the erosion of the Thar desert, whose dunes advance eastward into Haryana and the Aravalli gaps, and of the bare fields of the Deccan and the Punjab in the hot season. Glacial erosion and landslides affect the Himalaya, where road cutting and deforestation on steep slopes cause whole hillsides to slip in the monsoon, as at Darjeeling and in Uttarakhand. Coastal erosion by waves eats the beaches of Kerala and Odisha and the islands of the Sundarbans, where Lohachara and Ghoramara have been largely lost.
The regions of India most affected by erosion are the Himalayan and sub-Himalayan belt including the Shiwaliks and the Darjeeling hills; the Chambal, Yamuna and Mahi ravine lands; the Thar and its margins for wind erosion; the Chhotanagpur plateau and the laterite country of Jharkhand, Odisha and western Bengal; the Western Ghats and the black-soil slopes of the Deccan; and the north-eastern hills of jhum cultivation. The consequences are the loss of fertility and yield, the silting of reservoirs such as Maithon and Panchet on the Damodar, which have lost much of their storage, the raising of river beds and the increase of floods, the lowering of the water table because less rain soaks in, and the abandonment of ravined land.
- The Chambal ravines cover about 4.5 lakh hectares in Madhya Pradesh, Rajasthan and Uttar Pradesh; gullies 30 m deep advance several metres into the fields each year.
- The Ganga at Manikchak in Malda has eroded 200 sq km of land since 1970, swallowing villages and pushing the river bank eastward.
- Sheet erosion on the red-soil uplands of Purulia removes about 10-15 tonnes of soil per hectare a year, invisible from year to year but exhausting the field within a generation.
- Water erosion stages: sheet erosion (thin uniform layer) → rill erosion (small channels) → gully erosion (ravines); plus stream-bank erosion.
- Wind erosion: removal of fine particles from dry bare soil, chiefly in the Thar and its margins.
- Erosion-prone regions: Himalaya and Shiwaliks, Chambal-Yamuna ravines, Thar margins, Chhotanagpur and laterite belt, Western Ghats and Deccan slopes, north-eastern jhum hills.
Soil conservation: methods
Soil conservation is the protection of the soil from erosion and exhaustion and the restoration of land already damaged. Its principle is simple: keep the soil covered, slow the water and the wind, and put back what the crop takes out. The methods fall into three groups.
Biological or vegetative methods use plants. Afforestation and the protection of existing forests on hills and along rivers restore the canopy that breaks the rain and the roots that hold the soil; the planting of the Shiwalik slopes and the catchments of the Damodar reservoirs are examples. Shelter belts of trees planted in rows across the wind reduce its speed and stop the drifting of sand; the belts along the Indira Gandhi canal in Rajasthan and along the Sundarbans embankments serve this purpose. Controlled grazing and the growing of grass on waste land keep the cover. Crop rotation alternates exhausting crops such as rice or wheat with leguminous crops such as pulses that restore nitrogen; strip cropping plants alternate strips of close-growing crops such as grass or pulses between strips of row crops such as cotton across the slope, so that each strip traps the soil washed from the one above; mulching covers the bare soil with straw or leaves; and cover crops keep the field green through the storm season.
Mechanical or engineering methods reshape the land. Contour ploughing ploughs across the slope along the contour lines instead of up and down, so that each furrow is a small dam holding the water; contour bunding raises low earthen ridges along the contours for the same purpose on gentler slopes. Terracing cuts steep hillsides into level steps with a bund at the edge of each, the ancient method of the Himalaya, the Nilgiris and the north-eastern hills that makes rice possible on 30-degree slopes. Check dams of stone or earth built across gullies slow the water and trap the silt, so that the gully fills and can be planted; this is the treatment of the Chambal ravines. Gully plugging, the levelling of ravines, embankments along rivers, and proper drainage in irrigated land to prevent salinity all belong here.
Agronomic and policy measures complete the list: the regulation of shifting cultivation and its replacement by terraced or settled farming in the north-east; the reclamation of usar land with gypsum and drainage; the balanced use of organic manure and fertiliser; and watershed management, which treats a whole drainage basin from ridge to valley as one unit, combining afforestation at the top, bunds and terraces on the slopes and check dams in the streams. The Central Soil and Water Conservation Research and Training Institute at Dehradun, the Central Arid Zone Research Institute at Jodhpur and the Damodar Valley Corporation's soil conservation wing are the main agencies, and the Sukhomajri watershed in Haryana and the Ralegan Siddhi village in Maharashtra are the model successes.
- Ralegan Siddhi in Ahmednagar, Maharashtra, treated its watershed with check dams, contour bunds and afforestation from 1975 and raised its water table and its cropped area several times over.
- On the tea slopes of Darjeeling the bushes are planted in contour rows with drains across the slope, and shade trees keep the soil covered.
- A farmer on the red-soil slope of Purulia who ploughs along the contour and bunds the field edge keeps the monsoon rain on the field instead of losing it and the topsoil to the stream below.
- Biological methods: afforestation, shelter belts, controlled grazing, crop rotation, strip cropping, mulching, cover crops.
- Mechanical methods: contour ploughing, contour bunding, terracing, check dams, gully plugging, embankments, drainage.
- Watershed management = treating a whole drainage basin from ridge to valley as one conservation unit.
Soil fertility, degradation and the need for conservation
Beyond erosion, Indian soils are being degraded in other ways that the chapter groups under soil degradation, the decline in the quality of the soil. Nutrient depletion follows intensive cropping: a hectare of rice-wheat in the Punjab or rice-rice in Bengal removes more nitrogen, phosphorus and potash each year than is returned, and the deficiency of micro-nutrients such as zinc and sulphur is now widespread. The remedy is the balanced use of chemical fertiliser with organic manure, compost and green manure, and rotation with legumes, which fix nitrogen from the air. Salinisation and alkalinisation from canal irrigation without drainage, described above, affect about 7 million hectares. Waterlogging in the canal commands of Punjab, Haryana and the Ganga plain drowns the roots and brings salt to the surface. Acidification of the laterite and red soils under heavy rain and heavy ammonium fertiliser makes phosphorus unavailable and is corrected by liming. Chemical pollution from pesticides, industrial waste and urban sewage poisons soils near cities and factories, as in the Hooghly industrial belt. Loss of organic matter from the burning of crop residues and the disappearance of farmyard manure into fuel reduces the humus that holds water and nutrients.
Why conservation is necessary can be put in four sentences. Soil is practically non-renewable: a centimetre lost in a season takes centuries to form. India has little land to spare: 2.4 per cent of the world's land supports 18 per cent of its people, and the net sown area has stopped growing at about 140 million hectares, so every future increase in food must come from the same soil. The downstream costs of erosion, the silting of reservoirs, the raising of river beds and the floods that follow, fall on the whole country and not only on the farmer who loses the field. And a degraded soil holds less water, so drought is worse and the water table falls.
The Government's response includes the National Watershed Development Project for Rainfed Areas, the Integrated Watershed Management Programme, the Soil Health Card scheme of 2015 that tests each farmer's soil and prescribes fertiliser, the treatment of ravines and the reclamation of alkali land, and the National Mission for Sustainable Agriculture. The principle behind all of them is that conservation is cheaper than reclamation and that the soil, like the forest and the river, is held in trust for the next generation.
- A Soil Health Card for a field in Hooghly shows nitrogen low, phosphorus medium, potash high and zinc deficient, and recommends urea with zinc sulphate and a green manure crop of dhaincha before aman.
- The Maithon reservoir on the Barakar had lost about a quarter of its storage capacity to silt within thirty years of its completion in 1957 because the catchment was eroding.
- Green manuring: a crop of dhaincha grown for 45 days and ploughed in before rice adds 60-80 kg of nitrogen per hectare, replacing about 150 kg of urea.
- Soil degradation = decline in soil quality by nutrient depletion, salinisation, waterlogging, acidification, pollution and loss of organic matter, in addition to erosion.
- India: 2.4 per cent of the world's land, 18 per cent of its people; net sown area about 140 million hectares and no longer growing.
- Conservation is cheaper than reclamation: prevent erosion and exhaustion rather than restore ravined or saline land.
Key Concepts
- Soil
- The loose upper layer of the earth's crust made of weathered rock particles, humus, water and air, in which plants grow.
- Humus
- The dark decayed organic matter formed from dead plants and animals that binds soil particles and supplies nutrients.
- Leaching
- The downward removal of soluble minerals from the upper soil by percolating rainwater.
- Soil profile
- The vertical section of a soil from the surface to the bed rock, showing its horizons.
- Horizon
- One of the distinct layers of a soil profile, such as the A horizon (topsoil) or B horizon (subsoil).
- Sedentary soil
- A soil formed in place by the weathering of the rock beneath it, like the red and black soils of the peninsula.
- Transported soil
- A soil made of material carried from elsewhere by rivers, wind or ice, like the alluvium of the plains.
- Alluvial soil
- The fertile soil deposited by rivers, covering the northern plains and coastal deltas and about 43 per cent of India.
- Khadar
- The new alluvium of the flood plain, renewed by silt every year and the most fertile soil of the plains.
- Bhangar
- The old alluvium of the higher terraces above flood level, clayey and containing kankar nodules.
- Kankar
- Nodules of impure calcium carbonate found in the subsoil of old alluvium and dry-climate soils.
- Black soil (regur)
- The clayey black cotton soil of the Deccan lava plateau that holds moisture, swells when wet and cracks when dry.
- Red soil
- The sedentary soil of the peninsular granites and gneisses, coloured red by iron oxide and poor in nitrogen, phosphorus and humus.
- Laterite soil
- A red, brick-like soil of the humid tropics formed by leaching that leaves behind oxides of iron and aluminium.
- Desert soil
- The sandy, alkaline, salt-rich soil of the Thar and its margins, fertile only under irrigation.
- Saline soil (usar)
- A soil made infertile by salts that rise by capillary action where evaporation exceeds rainfall or irrigation lacks drainage.
- Soil erosion
- The removal of topsoil by running water, wind, ice or gravity faster than it can be formed.
- Gully erosion
- The cutting of deep channels or ravines into the land by concentrated running water, as in the Chambal ravines.
- Contour ploughing
- Ploughing across a slope along the contour lines so that every furrow holds back water and soil.
- Watershed management
- The conservation of soil and water by treating a whole drainage basin from ridge to valley as one unit.
End-of-Chapter Trial Paper & Test Questions
Topic-wise questions to test your understanding of every concept in this chapter.
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What is soil? Describe the factors that control its formation. / मृदा क्या है? इसके निर्माण को नियंत्रित करने वाले कारकों का वर्णन कीजिए।
Show answer
Soil is the loose uppermost layer of the earth's crust, formed of weathered rock particles mixed with humus, water and air, in which plants grow. Its formation is controlled by five factors. The parent rock supplies the mineral matter and decides the texture and chemistry, so basalt gives black soil and granite gives red soil. Climate is the most important factor: temperature governs the rate of weathering and the decay of humus, and rainfall governs leaching, so heavy rain produces laterite and low rain produces salty alkaline soil. Relief decides depth, thin on steep slopes and deep in valleys, and drainage. Natural vegetation and soil organisms supply humus, bind the soil and fix nitrogen. Time allows the profile to mature, so young flood silt has no horizons and old plateau soils have deep ones; human action such as ploughing, irrigation and deforestation is often counted as a sixth factor. / मृदा पृथ्वी की भूपर्पटी की सबसे ऊपरी ढीली परत है, जो अपक्षयित शैल कणों, ह्यूमस, जल और वायु से मिलकर बनी है और जिसमें पौधे उगते हैं। इसका निर्माण पाँच कारकों से नियंत्रित होता है। मूल शैल खनिज पदार्थ देती है और गठन तथा रसायन तय करती है, इसलिए बेसाल्ट से काली मृदा और ग्रेनाइट से लाल मृदा बनती है। जलवायु सबसे महत्वपूर्ण कारक है: तापमान अपक्षय और ह्यूमस के अपघटन की दर तय करता है, और वर्षा निक्षालन तय करती है, इसलिए भारी वर्षा से लैटेराइट और कम वर्षा से लवणीय क्षारीय मृदा बनती है। उच्चावच गहराई तय करता है, तीव्र ढालों पर पतली और घाटियों में गहरी, तथा अपवाह भी। प्राकृतिक वनस्पति और मृदा के जीव ह्यूमस देते हैं, मृदा को बाँधते हैं और नाइट्रोजन स्थिर करते हैं। समय परिच्छेदिका को परिपक्व होने देता है, इसलिए नई बाढ़ की गाद में संस्तर नहीं होते और पुरानी पठारी मृदाओं में गहरे संस्तर होते हैं; जुताई, सिंचाई और वनोन्मूलन जैसी मानवीय क्रिया को प्रायः छठा कारक माना जाता है।
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Draw a soil profile and describe its horizons. / मृदा परिच्छेदिका का चित्र बनाइए और इसके संस्तरों का वर्णन कीजिए।
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A soil profile is the vertical section of a soil from the surface down to the bed rock, and it consists of layers called horizons. At the top is the O horizon of litter, the undecayed leaves and grass, found under forest and grassland. Below it is the A horizon or topsoil, the darkest layer, richest in humus, most weathered, holding most roots and organisms, from which percolating water washes out soluble minerals and fine clay, so it is called the zone of eluviation. Next is the B horizon or subsoil, lighter in colour with less humus, which receives the clay, iron and lime washed down from above and is called the zone of illuviation; in dry climates it holds nodules of kankar. The A and B horizons together form the solum, the true soil. Below is the C horizon of weathered, broken parent material or regolith, and at the base the R horizon of solid unaltered bed rock. / मृदा परिच्छेदिका मृदा का सतह से आधार शैल तक का ऊर्ध्वाधर काट है, और इसमें संस्तर कहलाने वाली परतें होती हैं। सबसे ऊपर O संस्तर है, जिसमें अनपघटित पत्तियाँ और घास होती हैं और जो वन तथा घास भूमि के नीचे मिलता है। इसके नीचे A संस्तर या ऊपरी मृदा है, सबसे गहरे रंग की परत, ह्यूमस में सबसे समृद्ध, सबसे अधिक अपक्षयित, जिसमें अधिकांश जड़ें और जीव होते हैं, और जहाँ से रिसता जल घुलनशील खनिज और महीन चिकनी मिट्टी बहा ले जाता है, इसलिए इसे निक्षालन क्षेत्र कहते हैं। इसके बाद B संस्तर या अवमृदा है, हल्के रंग की और कम ह्यूमस वाली, जो ऊपर से बहकर आई चिकनी मिट्टी, लोहा और चूना ग्रहण करती है और संचयन क्षेत्र कहलाती है; शुष्क जलवायु में इसमें कंकड़ की गाँठें होती हैं। A और B संस्तर मिलकर सोलम, अर्थात वास्तविक मृदा बनाते हैं। नीचे C संस्तर अपक्षयित, टूटी मूल सामग्री या रेगोलिथ का है, और सबसे नीचे R संस्तर ठोस अपरिवर्तित आधार शैल का।
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Distinguish between bhangar and khadar. / भांगर और खादर में अंतर स्पष्ट कीजिए।
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Bhangar and khadar are the two types of alluvial soil of the northern plains, distinguished by age. Khadar is the new alluvium of the present flood plain lying in the low ground beside the rivers; it is renewed by fresh silt every monsoon, is light grey, sandy to loamy, porous, free of kankar and the most fertile soil of the plains, growing jute, rice and vegetables. Bhangar is the old alluvium of the higher terraces above the reach of the floods, deposited in an earlier period and not renewed; it is darker, more clayey, contains nodules of impure calcium carbonate called kankar, is harder to work and less fertile, though still good farm land. In West Bengal the Barind tract of Malda and Dinajpur is bhangar and the banks of the Bhagirathi are khadar. / भांगर और खादर उत्तरी मैदान की जलोढ़ मृदा के दो प्रकार हैं, जो आयु के आधार पर भिन्न हैं। खादर वर्तमान बाढ़ के मैदान की नई जलोढ़ मृदा है जो नदियों के किनारे निचली भूमि में मिलती है; इसे हर मानसून में ताजी गाद से नवीकृत किया जाता है, यह हल्की धूसर, बलुई से दोमट, सरंध्र, कंकड़ रहित और मैदानों की सबसे उपजाऊ मृदा है, जिसमें जूट, धान और सब्जियाँ उगती हैं। भांगर बाढ़ की पहुँच से ऊपर ऊँची वेदिकाओं की पुरानी जलोढ़ मृदा है, जो पहले के काल में जमा हुई और नवीकृत नहीं होती; यह गहरे रंग की, अधिक चिकनी, कंकड़ कहलाने वाली अशुद्ध कैल्शियम कार्बोनेट की गाँठों वाली, जोतने में कठिन और कम उपजाऊ है, यद्यपि अब भी अच्छी कृषि भूमि है। पश्चिम बंगाल में मालदा और दिनाजपुर का बरिंद क्षेत्र भांगर है और भागीरथी के किनारे खादर।
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Why is black soil suitable for cotton cultivation? Mention its distribution. / काली मृदा कपास की खेती के लिए उपयुक्त क्यों है? इसके वितरण का उल्लेख कीजिए।
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Black soil or regur suits cotton for several reasons. It is deep and very clayey, with 40-60 per cent clay, and therefore has a very high capacity to hold moisture: it absorbs the monsoon rain and retains it through the dry months, which the cotton plant needs for its long growing season of six to eight months, so cotton can be grown without irrigation in only 70-90 cm of rain. It is rich in lime, potash, iron and magnesium, which cotton requires, and its self-ploughing cracks in the dry season aerate the subsoil. It is found on the Deccan lava plateau: most of Maharashtra including the Vidarbha cotton belt, the Malwa plateau of Madhya Pradesh, Saurashtra and Kathiawar in Gujarat, northern Karnataka, western Telangana and Rayalaseema in Andhra Pradesh, covering about 15 per cent of India. / काली मृदा या रेगुर कई कारणों से कपास के लिए उपयुक्त है। यह गहरी और अत्यंत चिकनी है, जिसमें 40-60 प्रतिशत क्ले होती है, और इसलिए इसकी नमी धारण क्षमता बहुत अधिक है: यह मानसून की वर्षा को सोख लेती है और शुष्क महीनों में उसे बनाए रखती है, जो कपास के पौधे को उसके छह से आठ महीने के लंबे वर्धन काल के लिए चाहिए, अतः केवल 70-90 सेमी वर्षा में बिना सिंचाई के कपास उगाई जा सकती है। यह चूना, पोटाश, लोहा और मैग्नीशियम में समृद्ध है, जो कपास को चाहिए, और शुष्क ऋतु में इसकी स्व-जुताई वाली दरारें अवमृदा में वायु पहुँचाती हैं। यह दक्कन के लावा पठार पर मिलती है: विदर्भ कपास पेटी सहित महाराष्ट्र का अधिकांश भाग, मध्य प्रदेश का मालवा पठार, गुजरात का सौराष्ट्र और काठियावाड़, उत्तरी कर्नाटक, पश्चिमी तेलंगाना और आंध्र प्रदेश का रायलसीमा, जो भारत के लगभग 15 प्रतिशत भाग को ढकती है।
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How is laterite soil formed? Why is it less fertile? / लैटेराइट मृदा का निर्माण कैसे होता है? यह कम उपजाऊ क्यों है?
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Laterite soil forms in the humid tropics where high temperature and heavy rainfall of more than 200 cm alternate with a marked dry season. The heavy rain leaches the silica, lime, potash and other soluble bases down and out of the soil, and in the dry season capillary action draws the water back up, leaving behind a concentration of the insoluble oxides of iron and aluminium at the surface, which give the soil its red colour and make it harden like a brick when dry, the origin of its name from the Latin 'later'. It is less fertile because the leaching has removed the nitrogen, phosphorus, potash and lime that plants need, the high temperature destroys the bacteria and the humus, so organic matter is low, and the soil is acidic, coarse and unable to hold water. It grows cashew, tapioca, tea and coffee with heavy manuring, and is found on the Western Ghats, the Chhotanagpur margin and the rarh districts of West Bengal. / लैटेराइट मृदा आर्द्र उष्णकटिबंध में बनती है जहाँ उच्च तापमान और 200 सेमी से अधिक भारी वर्षा के साथ स्पष्ट शुष्क ऋतु बारी-बारी से आती है। भारी वर्षा सिलिका, चूना, पोटाश और अन्य घुलनशील क्षारों को मृदा से नीचे बहाकर बाहर कर देती है, और शुष्क ऋतु में केशिका क्रिया जल को वापस ऊपर खींचती है, जिससे सतह पर लोहे और ऐलुमिनियम के अघुलनशील ऑक्साइडों का संकेंद्रण रह जाता है, जो मृदा को उसका लाल रंग देते हैं और सूखने पर ईंट जैसा कठोर बना देते हैं, जिससे लैटिन 'लेटर' से इसका नाम पड़ा। यह कम उपजाऊ इसलिए है कि निक्षालन ने पौधों को आवश्यक नाइट्रोजन, फास्फोरस, पोटाश और चूना हटा दिया है, उच्च तापमान जीवाणुओं और ह्यूमस को नष्ट कर देता है जिससे जैविक पदार्थ कम रहता है, और मृदा अम्लीय, मोटी और जल न रोक पाने वाली है। भारी खाद के साथ इसमें काजू, टैपिओका, चाय और कॉफी उगते हैं, और यह पश्चिमी घाट, छोटानागपुर के किनारे और पश्चिम बंगाल के राढ़ जिलों में मिलती है।
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Compare red soil and laterite soil. / लाल मृदा और लैटेराइट मृदा की तुलना कीजिए।
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Both are soils of the peninsular plateau, both are coloured by iron oxide, both are poor in nitrogen, phosphorus and humus, and both are acidic and need manure, but they differ in origin and character. Red soil is a sedentary soil formed by the ordinary weathering of granite and gneiss under moderate rainfall, is sandy to loamy and friable, and covers about 18 per cent of India in Tamil Nadu, Karnataka, Andhra Pradesh, Odisha, Jharkhand and south-western Bengal, growing ragi, groundnut, pulses and irrigated rice. Laterite is formed by the intense leaching of any rock under rainfall above 200 cm with a dry season, is a coarse, nodular, brick-hard soil rich in iron and aluminium oxides, covers only about 3.7 per cent of India on the Western Ghats, the Chhotanagpur margin and the rarh of Bengal, and grows cashew, tapioca and plantation crops; it is the poorer of the two and is more liable to gully erosion. / दोनों प्रायद्वीपीय पठार की मृदाएँ हैं, दोनों लौह ऑक्साइड से रंगी हैं, दोनों नाइट्रोजन, फास्फोरस और ह्यूमस में निर्धन हैं, और दोनों अम्लीय हैं तथा खाद माँगती हैं, परंतु उत्पत्ति और स्वभाव में भिन्न हैं। लाल मृदा मध्यम वर्षा में ग्रेनाइट और नाइस के साधारण अपक्षय से बनी स्थानिक मृदा है, बलुई से दोमट और भुरभुरी है, और तमिलनाडु, कर्नाटक, आंध्र प्रदेश, ओडिशा, झारखंड और दक्षिण-पश्चिमी बंगाल में भारत के लगभग 18 प्रतिशत भाग पर फैली है, जिसमें रागी, मूँगफली, दालें और सिंचित धान उगते हैं। लैटेराइट 200 सेमी से अधिक वर्षा और शुष्क ऋतु में किसी भी शैल के तीव्र निक्षालन से बनती है, लोहे और ऐलुमिनियम के ऑक्साइडों से भरी मोटी, गाँठदार, ईंट-सी कठोर मृदा है, पश्चिमी घाट, छोटानागपुर के किनारे और बंगाल के राढ़ में भारत के केवल लगभग 3.7 प्रतिशत भाग पर है, और इसमें काजू, टैपिओका और बागानी फसलें उगती हैं; यह दोनों में अधिक निर्धन है और अवनालिका अपरदन की अधिक शिकार होती है।
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Describe the soils of West Bengal. / पश्चिम बंगाल की मृदाओं का वर्णन कीजिए।
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West Bengal's soils lie in belts from north to south. The Darjeeling hills have thin, brown, acidic, humus-rich mountain soil on which tea grows. The Terai and Duars at the foot of the hills have coarse gravelly soil near the hills becoming dark, waterlogged, peaty loam farther out, growing tea, rice, jute and pineapple. The Barind tract of Malda and the Dinajpurs is old alluvium, grey to reddish clay with kankar, growing one crop of aman rice and mango. The Ganga plain and delta from Murshidabad and Bardhaman to Hooghly, Kolkata and the 24 Parganas has fertile new alluvium, grey silty loam renewed by floods, growing rice, jute, potato and vegetables in two or three crops a year. The Rarh districts of Purulia, Bankura, Birbhum, western Bardhaman and Paschim Medinipur have red and laterite soil, gravelly, acidic and poor, growing rain-fed aman and sal forest. The Sundarbans and the coast have saline, marshy clay under mangrove and salt-tolerant rice. / पश्चिम बंगाल की मृदाएँ उत्तर से दक्षिण तक पेटियों में हैं। दार्जिलिंग की पहाड़ियों में पतली, भूरी, अम्लीय, ह्यूमस से भरी पर्वतीय मृदा है जिस पर चाय उगती है। पहाड़ियों की तलहटी के तराई और डुआर्स में पहाड़ के पास मोटी बजरी वाली मृदा है जो आगे गहरी, जलमग्न, पीटयुक्त दोमट बन जाती है, जिसमें चाय, धान, जूट और अनानास उगते हैं। मालदा और दोनों दिनाजपुर का बरिंद क्षेत्र पुरानी जलोढ़ मृदा है, धूसर से लालिमा लिए कंकड़ वाली चिकनी, जिसमें अमन धान की एक फसल और आम होता है। मुर्शिदाबाद और बर्धमान से हुगली, कोलकाता और 24 परगना तक गंगा के मैदान और डेल्टा में उपजाऊ नई जलोढ़ मृदा है, बाढ़ से नवीकृत धूसर गादयुक्त दोमट, जिसमें वर्ष में दो-तीन फसलों में धान, जूट, आलू और सब्जियाँ उगती हैं। पुरुलिया, बाँकुड़ा, बीरभूम, पश्चिमी बर्धमान और पश्चिम मेदिनीपुर के राढ़ जिलों में लाल और लैटेराइट मृदा है, बजरी वाली, अम्लीय और निर्धन, जिसमें वर्षा-आधारित अमन और साल वन होते हैं। सुंदरबन और तट पर मैंग्रोव और लवण-सहिष्णु धान के नीचे लवणीय, दलदली चिकनी मृदा है।
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What is soil erosion? Explain its main causes in India. / मृदा अपरदन क्या है? भारत में इसके मुख्य कारण समझाइए।
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Soil erosion is the removal of the topsoil by running water, wind, ice or gravity at a rate faster than the soil can be formed; it affects about 130 million hectares of India, which lose some 5,300 million tonnes of soil a year. Its natural causes are the torrential monsoon rain that falls on bare fields at the end of the dry season, the steep slopes of the Himalaya and the Ghats, the loose texture of the alluvium and sandy soils, the strong hot-season winds of the north-west and the shifting of the plain rivers. Its human causes are more serious: deforestation of the hills for timber, fuel and farming removes the canopy and the binding roots; overgrazing by huge herds strips the grass cover; shifting cultivation in the north-east clears and burns steep slopes; faulty farming such as ploughing up and down the slope, bare fallows and over-irrigation loosens and exposes the soil; and mining, quarrying, roads and construction lay bare large areas, while population pressure pushes cultivation onto land that should stay under grass or forest. / मृदा अपरदन बहते जल, पवन, हिम या गुरुत्व द्वारा ऊपरी मृदा को उसके बनने की दर से तेज हटाना है; यह भारत के लगभग 13 करोड़ हेक्टेयर को प्रभावित करता है, जो प्रति वर्ष लगभग 530 करोड़ टन मृदा खोते हैं। इसके प्राकृतिक कारण हैं शुष्क ऋतु के अंत में नंगे खेतों पर गिरने वाली मूसलाधार मानसूनी वर्षा, हिमालय और घाटों के तीव्र ढाल, जलोढ़ और बलुई मृदाओं का ढीला गठन, उत्तर-पश्चिम की प्रबल ग्रीष्मकालीन पवनें और मैदानी नदियों का मार्ग बदलना। इसके मानवीय कारण अधिक गंभीर हैं: इमारती लकड़ी, ईंधन और खेती के लिए पहाड़ियों का वनोन्मूलन छत्र और बाँधने वाली जड़ों को हटा देता है; विशाल झुंडों का अतिचारण घास का आवरण छीन लेता है; उत्तर-पूर्व में स्थानांतरी कृषि तीव्र ढालों को साफ कर जलाती है; ढाल के ऊपर-नीचे जुताई, नंगी परती और अति-सिंचाई जैसी दोषपूर्ण खेती मृदा को ढीला और अनावृत करती है; और खनन, पत्थर खनन, सड़कें और निर्माण बड़े क्षेत्रों को नंगा कर देते हैं, जबकि जनसंख्या का दबाव खेती को उस भूमि पर धकेलता है जिसे घास या वन के नीचे रहना चाहिए।
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Distinguish between sheet erosion and gully erosion. / परत अपरदन और अवनालिका अपरदन में अंतर बताइए।
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Sheet erosion is the removal of a thin, nearly uniform layer of topsoil from the whole surface of a slope by rain wash; it is the first stage of water erosion, is hard to notice because the field looks unchanged, and shows only in the gradual paling of the soil as the dark humus layer is lost, yet over large areas it is the most damaging form. Gully erosion is the final stage, reached after the water has gathered into rills: the channels deepen and widen into gullies too large to plough across, which grow headward into the field every monsoon and cut the land into steep-sided ravines that are lost to farming altogether, as in the Chambal ravines of Madhya Pradesh and the laterite badlands of Bankura and Paschim Medinipur. Sheet erosion is checked by cover crops, mulching and contour ploughing; gully erosion needs check dams, gully plugging and afforestation. / परत अपरदन वर्षा के बहाव द्वारा ढाल की पूरी सतह से ऊपरी मृदा की एक पतली, लगभग समान परत का हटना है; यह जल अपरदन की पहली अवस्था है, इसे पहचानना कठिन है क्योंकि खेत अपरिवर्तित दिखता है, और यह केवल गहरी ह्यूमस परत के खोने से मृदा के धीरे-धीरे फीके पड़ने में दिखता है, फिर भी बड़े क्षेत्रों में यह सबसे हानिकारक रूप है। अवनालिका अपरदन अंतिम अवस्था है, जो जल के छोटी नालियों में इकट्ठा होने के बाद आती है: नालियाँ गहरी और चौड़ी होकर ऐसी अवनालिकाएँ बन जाती हैं जिनके आर-पार जुताई नहीं हो सकती, जो हर मानसून में खेत के भीतर बढ़ती जाती हैं और भूमि को खड़ी दीवारों वाले खड्डों में काट देती हैं जो खेती से पूरी तरह छिन जाते हैं, जैसे मध्य प्रदेश के चंबल के खड्ड और बाँकुड़ा तथा पश्चिम मेदिनीपुर की लैटेराइट बंजर भूमि। परत अपरदन को आवरण फसलों, पलवार और समोच्च जुताई से रोका जाता है; अवनालिका अपरदन के लिए रोक बाँध, अवनालिका भराव और वनरोपण चाहिए।
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Describe the methods of soil conservation. / मृदा संरक्षण की विधियों का वर्णन कीजिए।
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Soil conservation protects the soil from erosion and exhaustion by keeping it covered, slowing water and wind and returning what crops remove. Biological methods use plants: afforestation and forest protection on hills and river banks, shelter belts of trees across the wind in dry regions, controlled grazing, crop rotation with nitrogen-fixing legumes, strip cropping of close-growing and row crops across the slope, mulching and cover crops. Mechanical methods reshape the land: contour ploughing and contour bunding across the slope so that furrows and ridges hold back water, terracing of steep hillsides into level steps as in the Himalaya and the Nilgiris, check dams across gullies to trap silt as in the Chambal ravines, gully plugging, embankments and proper drainage in irrigated land to prevent salinity. Policy measures include regulating shifting cultivation, reclaiming usar land with gypsum, balanced manuring and watershed management that treats a whole drainage basin as one unit, as at Ralegan Siddhi and Sukhomajri. / मृदा संरक्षण मृदा को ढके रखकर, जल और पवन को धीमा करके तथा फसलों द्वारा लिया गया लौटाकर उसे अपरदन और क्षय से बचाता है। जैविक विधियाँ पौधों का उपयोग करती हैं: पहाड़ियों और नदी तटों पर वनरोपण और वन संरक्षण, शुष्क क्षेत्रों में पवन के आर-पार वृक्षों की रक्षक पट्टियाँ, नियंत्रित चराई, नाइट्रोजन स्थिर करने वाली दलहनों के साथ फसल चक्र, ढाल के आर-पार सघन और कतार वाली फसलों की पट्टीदार खेती, पलवार और आवरण फसलें। यांत्रिक विधियाँ भूमि का आकार बदलती हैं: ढाल के आर-पार समोच्च जुताई और समोच्च मेड़बंदी ताकि कूँड़ और मेड़ें जल रोकें, हिमालय और नीलगिरि की तरह तीव्र ढालों की समतल सीढ़ियों में सोपानी खेती, चंबल के खड्डों की तरह गाद रोकने के लिए अवनालिकाओं पर रोक बाँध, अवनालिका भराव, तटबंध और लवणता रोकने के लिए सिंचित भूमि में उचित जल निकास। नीतिगत उपायों में स्थानांतरी कृषि का नियमन, जिप्सम से ऊसर भूमि का सुधार, संतुलित खाद और जलसंभर प्रबंधन शामिल है जो पूरे अपवाह बेसिन को एक इकाई मानता है, जैसे रालेगण सिद्धि और सुखोमाजरी में।
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Why is soil conservation necessary in India? / भारत में मृदा संरक्षण क्यों आवश्यक है?
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Soil conservation is necessary in India for four reasons. First, soil is practically non-renewable: 2.5 cm of topsoil takes 200 to 1,000 years to form and one monsoon on a bare slope can remove it, and 130 million hectares are already eroding. Second, India has little land to spare, since 2.4 per cent of the world's land feeds 18 per cent of its people and the net sown area has stopped growing at about 140 million hectares, so every future increase in food must come from the same soil, whose fertility erosion, salinity and nutrient depletion are reducing. Third, the downstream costs fall on everyone: eroded silt fills reservoirs such as Maithon and Panchet, raises river beds and worsens floods in the Ganga and Damodar plains. Fourth, a degraded soil holds less water, so less rain soaks in, the water table falls and drought becomes more severe. Conservation is far cheaper than reclaiming ravined or saline land, and the soil is held in trust for the next generation. / भारत में मृदा संरक्षण चार कारणों से आवश्यक है। पहला, मृदा व्यावहारिक रूप से अनवीकरणीय है: 2.5 सेमी ऊपरी मृदा बनने में 200 से 1,000 वर्ष लगते हैं और नंगे ढाल पर एक मानसून उसे हटा सकता है, और 13 करोड़ हेक्टेयर पहले से ही अपरदित हो रहे हैं। दूसरा, भारत के पास अतिरिक्त भूमि कम है, क्योंकि विश्व की 2.4 प्रतिशत भूमि उसकी 18 प्रतिशत जनसंख्या का पेट भरती है और शुद्ध बोया क्षेत्र लगभग 14 करोड़ हेक्टेयर पर रुक गया है, इसलिए भोजन में हर भावी वृद्धि उसी मृदा से आनी है, जिसकी उर्वरता को अपरदन, लवणता और पोषक क्षय घटा रहे हैं। तीसरा, अनुप्रवाह की लागत सब पर पड़ती है: अपरदित गाद मैथन और पंचेत जैसे जलाशयों को भरती है, नदी तल ऊँचा करती है और गंगा तथा दामोदर के मैदानों में बाढ़ बढ़ाती है। चौथा, निम्नीकृत मृदा कम जल रोकती है, इसलिए कम वर्षा रिसती है, भूजल स्तर गिरता है और सूखा अधिक गंभीर हो जाता है। संरक्षण खड्डों वाली या लवणीय भूमि के सुधार से कहीं सस्ता है, और मृदा अगली पीढ़ी की धरोहर है।
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Why do the soils of the Sundarbans become saline, and how does this affect agriculture? / सुंदरबन की मृदाएँ लवणीय क्यों हो जाती हैं, और इसका कृषि पर क्या प्रभाव पड़ता है?
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The Sundarbans is the tidal part of the Ganga delta, where the rivers are brackish and the sea rises twice a day over the low islands; sea water enters the soil directly through tidal creeks and through the seepage beneath the embankments, and in the dry season the high water table and strong evaporation draw salt up to the surface by capillary action, leaving a crust. Cyclones such as Aila in 2009 and Amphan in 2020 breach the embankments and flood the fields with salt water that stands for weeks. The effect on agriculture is severe: salt in the root zone prevents the plants from absorbing water, so only one crop of salt-tolerant aman rice can be grown in the monsoon when the rain washes the salt down, the fields stay barren in the dry season, and after a cyclone rice will not grow for one or two years until the salt is leached out. Farmers respond with embankments, freshwater ponds, salt-tolerant rice varieties, drainage and the addition of gypsum. / सुंदरबन गंगा डेल्टा का ज्वारीय भाग है, जहाँ नदियाँ खारी हैं और समुद्र दिन में दो बार निचले द्वीपों पर चढ़ता है; समुद्री जल ज्वारीय खाड़ियों से सीधे और तटबंधों के नीचे रिसाव से मृदा में प्रवेश करता है, और शुष्क ऋतु में ऊँचा भूजल स्तर तथा तीव्र वाष्पीकरण केशिका क्रिया से लवण को सतह तक खींचकर पपड़ी छोड़ देते हैं। 2009 के आइला और 2020 के अम्फान जैसे चक्रवात तटबंध तोड़कर खेतों को खारे जल से भर देते हैं जो हफ्तों खड़ा रहता है। कृषि पर इसका प्रभाव गंभीर है: जड़ क्षेत्र का लवण पौधों को जल सोखने से रोकता है, इसलिए केवल मानसून में, जब वर्षा लवण को नीचे बहा देती है, लवण-सहिष्णु अमन धान की एक फसल हो पाती है, शुष्क ऋतु में खेत बंजर रहते हैं, और चक्रवात के बाद एक-दो वर्ष तक, जब तक लवण निक्षालित न हो जाए, धान नहीं उगता। किसान तटबंधों, मीठे पानी के तालाबों, लवण-सहिष्णु धान की किस्मों, जल निकास और जिप्सम मिलाकर इसका सामना करते हैं।
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