Overview
Previous Year UPSC-CSE Questions By the end you will be able to draft model answers for the following UPSC questions. Each question carries a collapsible framework showing how to approach it in the exam.
- UPSC Mains 2013 GS-IThere is no formation of deltas by rivers of the Western Ghat. Why?
How to structure the answer in the exam
Introduction: Most west-flowing rivers of the Western Ghat, with the exception of the Narmada and Tapi, reach the Arabian Sea through estuaries rather than building deltas, a pattern set by the gradient, course length, and tectonic setting of the western margin.
Body (sub-themes to develop):
- Steep westward gradient: the short, rapid descent from the Western Ghat crestline to the Arabian Sea limits sediment deposition near the mouth.
- Short course and limited sediment: most west-flowing rivers run a short distance and carry a smaller sediment load than the long east-flowing rivers.
- Rifted-margin tectonics: the Western Ghat is a faulted escarpment from the break-up of Gondwana, producing a narrow continental shelf with a rapid offshore drop that leaves little room for delta lobes.
- Contrast with the east coast: the Mahanadi, Godavari, Krishna, and Kaveri flow east on a gentler gradient over longer courses to a wider shelf, so they build lobate deltas at the Bay of Bengal.
Conclusion: Delta formation depends on abundant sediment meeting a low-energy, shallow-shelf coast; the Western Ghat rivers meet none of these conditions, which is why their mouths are estuarine while the east-flowing rivers are deltaic.
Alluvial soil is the river-deposited soil that covers nearly 40 per cent of the Indian land surface, the single most extensive soil group in the country. It spreads across the Indo-Gangetic-Brahmaputra plains in the north and the coastal-deltaic tracts of the peninsular coast. The soil is depositional rather than residual: rivers descending from the Himalayas and the peninsular plateau carry weathered debris downstream and lay it down on flood plains, terraces, and deltas. Two sub-types are recognised by terrace position. Khadar is the new alluvium replenished annually by flood waters; Bhangar is the older alluvium of higher terraces that carries calcareous nodules called kankar. The soil group dominates the Entisols and Inceptisols orders of the soil taxonomy used in India.
Background and Historical Context
Alluvial soil supports the country's most intensive grain cultivation. The Indo-Gangetic plain produces a disproportionate share of India's rice and wheat, sustains the canal irrigation of Punjab and Haryana, and underwrites food security from the Green Revolution to the present-day Public Distribution System. UPSC Prelims tests alluvial-soil links with river systems and cropping patterns; Mains GS-I treats deposition as a foundation of agricultural geography.
What is the significance of mastering alluvial-soil geography? Three dimensions follow. Sub-type discrimination explains why Khadar tracts near current channels stay fertile every year while Bhangar terraces accumulate kankar that hinders deep-rooted crops. The west-to-east sand-content gradient from Punjab to the lower Ganga plain explains the changing crop mix. The coastal-deltaic variant connects alluvial geography to deltaic agriculture and to delta-erosion risks that rising sea levels now amplify.
The Indo-Gangetic belt is central to the Soil Health Card scheme, the per-drop-more-crop water-efficiency programme under PMKSY, and the National Mission for Sustainable Agriculture. The ICAR-Indian Institute of Soil Science at Bhopal and the National Bureau of Soil Survey and Land Use Planning at Nagpur map and study the belt. Sustainability concerns now dominate: groundwater overdraft in Punjab and Haryana, fertiliser-overuse nutrient imbalance, and Khadar encroachment by urban expansion near the National Capital Region.
Introduction: Alluvial Soil as India's Most Cultivated Soil Group
Definition and spatial extent
Alluvial soil is the depositional soil that rivers lay down as they descend from the highlands and lose energy on the plains. Unlike residual soils that form in place from weathered parent rock, alluvial soils owe their texture and fertility to the transport history of the river that deposited them.
The Himalayan rivers, the Indus, Ganga, and Brahmaputra with their tributaries, supply the bulk of the Indian alluvial belt. The peninsular rivers, the Mahanadi, Godavari, Krishna, and Kaveri, extend the belt into coastal-deltaic settings on the eastern seaboard.
The alluvial cover spreads across nearly 40 per cent of the country's land surface, the largest single soil group in India. Three settings host it: the Indo-Gangetic-Brahmaputra plains in the north, the east-coast deltaic tract from the Mahanadi to the Kaveri, and a narrower west-coast strip along the Konkan and Malabar coasts.
Formation: Riverine Deposition Across Three Settings
How alluvium accumulates in plains, deltas, and coasts
The depositional process is the same in principle across all three settings. A river carrying suspended sediment slows on a gentler gradient, loses transport capacity, and drops its load on the flood plain or in the delta. The character of the resulting alluvium depends on the energy at the point of deposition.
- (i) Indo-Gangetic-Brahmaputra plain: The principal alluvial belt from Punjab through Uttar Pradesh, Bihar, West Bengal, and the Brahmaputra valley of Assam; built by the Himalayan rivers since the Pleistocene over the foredeep created by Himalayan uplift.
- (ii) East-coast deltaic tract: The lobate deposits where the Mahanadi, Godavari, Krishna, and Kaveri reach the Bay of Bengal; marked by distributary channels and very fine clay-silt textures from low-energy deposition.
- (iii) West-coast strip: A narrower alluvial fringe along the Konkan and Malabar coasts; the steep gradient of west-flowing peninsular rivers prevents broad delta formation here.
The Indo-Gangetic belt dominates by area and by economic weight. Coastal alluvium adds critical agricultural tracts on the eastern seaboard but holds a smaller share of the national alluvial area.
The Two Sub-types: Khadar and Bhangar
Khadar (new alluvium) and Bhangar (older alluvium with kankar)
Classification by terrace position and depositional age yields two operationally important sub-types. Each carries a distinct fertility profile and a distinct management challenge for the cultivator.
- (i) Khadar (new alluvium): The young alluvium of current flood plains, lying near active river channels; replenished annually by monsoon flood silt; finer-textured and lighter in colour; the more fertile sub-type for intensive cultivation, but exposed to flood-damage risk each monsoon.
- (ii) Bhangar (older alluvium): The older alluvium of higher terraces lifted above the current flood reach, standing some thirty metres above the flood level; more clayey and darker in the standard NCERT description; it carries beds of kankar (calcareous lime nodules) a few metres below the terrace surface; less fertile per unit area but safer from flooding.
Both sub-types are alluvial, yet the kankar concentration is markedly higher in Bhangar because the older terrace has had longer for lime to leach downward and settle as nodules. A hard kankar layer can impede deep-rooted crops and may require breaking before mechanised cultivation.
| Feature | Khadar (new alluvium) | Bhangar (old alluvium) |
|---|---|---|
| Terrace position | Active flood plain near channels | Higher terrace above flood level |
| Flood replenishment | Replenished annually by floods | Above flood reach, not replenished |
| Texture and colour | Finer, lighter coloured | More clayey, darker (NCERT) |
| Kankar (lime nodules) | Largely absent | Present in beds below the terrace |
| Relative fertility | More fertile | Less fertile per unit area |
Characteristics: Texture, Nutrients, and the West-to-East Gradient
Texture, nutrient profile, and the west-to-east sand-content gradient
Observable outcomes of the depositional regime. Three properties follow from the river-deposition process and shape the agricultural geography of the alluvial belt across northern India.
- (a) Colour and texture: Light grey to ash-grey in the Indo-Gangetic belt; the sand fraction falls steadily from west to east, from the coarser sandy loams of Punjab and Haryana to the finer silts and clays of the lower Ganga and the Brahmaputra valley. The gradient explains why wheat leads in the west and rice leads in the east.
- (b) Nutrient profile: Generally rich in potash, phosphoric acid, and lime, but deficient in nitrogen and organic humus. The deficiency drives the heavy nitrogenous-fertiliser use of the rice-wheat belt and the resulting groundwater nitrate concerns.
- (c) Drainage and structure: Variable; Khadar in active flood plains drains fast in dry months and floods in the monsoon; Bhangar terraces drain steadily; deltaic alluvium holds water and supports paddy but suffers waterlogging and coastal salinity ingress.
The combined profile yields a soil that is intensively cultivable yet nitrogen-hungry. The Indo-Gangetic belt carries the heaviest fertiliser use per hectare in the country, with the related concerns of nutrient run-off and groundwater contamination.
Agricultural Significance and Management Challenges
Crop economy and sustainability concerns
The alluvial belt underwrites the bulk of India's grain production. Rice and wheat together occupy a disproportionate share of the cropped area on Indo-Gangetic alluvium; sugarcane, jute, oilseeds, and pulses extend the mix; deltaic alluvium of the east coast carries further rice and horticulture.
- Rice and wheat: The dominant rotation across the Indo-Gangetic belt; the Green Revolution was built on the alluvial soils of Punjab and Haryana.
- Sugarcane: Concentrated in western Uttar Pradesh and parts of Bihar; the potash-rich alluvium supports this perennial, high-water-demand crop.
- Jute: The fibre crop concentrates in the Ganga-Brahmaputra delta, where fine silt and heavy rainfall combine to yield long fibre.
- Pulses and oilseeds: Add nitrogen-fixing rotations; promoted by the National Mission for Sustainable Agriculture to ease the nutrient imbalance of the rice-wheat rotation.
Sustainability concerns now dominate the agenda. Groundwater overdraft in the canal commands of Punjab and Haryana, fertiliser-overuse nutrient imbalance and nitrate contamination, Khadar encroachment by urban expansion near the National Capital Region, and sea-level-rise salinity in the Sundarbans and the east-coast deltas together set the alluvial-belt policy agenda for this decade.
Prelims MCQ practice
Each question below tests one specific concept on the topic. Click to reveal the answer and a full option-wise explanation.
Q1. Consider the following statements about alluvial soils in India:
- Alluvial soils cover the Indo-Gangetic Plain, the Brahmaputra valley, and the coastal deltaic tracts.
- Alluvial soils are the most extensive soil type in India by geographic coverage.
- Alluvial soils form primarily through in-situ chemical weathering of granite under a tropical-humid climate.
Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer and explanation
Answer: 1 and 2 only
Explanation.
Correct: a (1 and 2 only). Statement 1 is correct: alluvial soils cover the Indo-Gangetic plain, the Brahmaputra valley, and the coastal deltas. Statement 2 is correct: alluvial soils are the most extensive Indian soil type, around 40 per cent of land area. Statement 3 is wrong: alluvial soils are depositional soils formed by river-borne sediment transport, NOT in-situ weathering; in-situ weathering produces residual soils such as laterite and black soil.
Q2. Consider the following statements about Khadar and Bhangar alluvial soils:
- Khadar is the new alluvium deposited annually by floods and is found near current river channels.
- Bhangar is the older alluvium of upland terraces above the active flood plain and is generally darker and more clayey.
- Khadar is generally less fertile than Bhangar because it lacks annual sediment replenishment.
Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer and explanation
Answer: 1 and 2 only
Explanation.
Correct: a (1 and 2 only). Statement 1 is correct: Khadar is annually-flood-deposited new alluvium near active channels. Statement 2 is correct: Bhangar is older terrace alluvium above the flood plain, generally darker and more clayey in the standard description. Statement 3 is wrong: Khadar is more fertile than Bhangar precisely because of annual flood replenishment; Bhangar has been leached longer and accumulates kankar (lime nodules).
Q3. Consider the following statements about deltaic alluvial soils:
- Deltaic soils of the Ganga-Brahmaputra delta (Sundarbans), the Godavari-Krishna delta, the Mahanadi delta, and the Kaveri delta support intensive rice cultivation.
- Deltaic soils are typically fine-textured silty clay because fine sediment settles at low-energy river mouths.
Which of the statements given above is/are correct?
- 1 only
- 2 only
- Both 1 and 2
- Neither 1 nor 2
Show answer and explanation
Answer: Both 1 and 2
Explanation.
Correct: c (Both 1 and 2). Statement 1 is correct: India's major delta tracts support intensive rice cultivation. Statement 2 is correct: deltaic soils are typically silty clay because fine sediment is deposited in the low-energy river-mouth setting.
Q4. Consider the following statements about the chemical properties of Indian alluvial soils:
- Alluvial soils are rich in potash and lime but generally deficient in nitrogen and humus.
- Alluvial soils show a wide pH range from slightly acidic to slightly alkaline across their geographic extent.
Which of the statements given above is/are correct?
- 1 only
- 2 only
- Both 1 and 2
- Neither 1 nor 2
Show answer and explanation
Answer: Both 1 and 2
Explanation.
Correct: c (Both 1 and 2). Statement 1 is correct: alluvial soils are typically rich in potash and lime but deficient in nitrogen and humus, so nitrogen fertilisation is central to the wheat-rice package. Statement 2 is correct: alluvial soils span slightly acidic to slightly alkaline pH, with the upper Ganga tract trending alkaline and the eastern (Bengal) tract trending slightly acidic.
Q5. Consider the following statements about the state-wise distribution of alluvial soils in India:
- Punjab, Haryana, Uttar Pradesh, Bihar, and West Bengal are dominated by alluvial soils.
- Assam (Brahmaputra valley), Andhra Pradesh (Godavari-Krishna delta), and Tamil Nadu (Kaveri delta) also have significant alluvial extent.
- The Deccan plateau interior of Madhya Pradesh is dominated by alluvial soils.
Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer and explanation
Answer: 1 and 2 only
Explanation.
Correct: a (1 and 2 only). Statement 1 is correct: the Indo-Gangetic states are alluvial-dominated. Statement 2 is correct: Assam, Andhra Pradesh, and Tamil Nadu also carry significant alluvial extent. Statement 3 is wrong: the Deccan plateau interior of Madhya Pradesh is dominated by black soil (regur), not alluvium; alluvial soils in the state are limited to the Narmada and Chambal valleys.
Q6. Consider the following statements about cropping patterns on alluvial soils:
- Alluvial soils support the wheat-rice rotation of the Indo-Gangetic belt.
- Sugarcane, jute, oilseeds, and pulses are also widely grown on alluvial soils.
- Alluvial soils are agronomically unsuitable for any commercial crop and support only subsistence millet cultivation.
Which of the statements given above are correct?
- 1 and 2 only
- 2 and 3 only
- 1 and 3 only
- 1, 2 and 3
Show answer and explanation
Answer: 1 and 2 only
Explanation.
Correct: a (1 and 2 only). Statement 1 is correct: alluvial soils support the Indo-Gangetic wheat-rice rotation. Statement 2 is correct: sugarcane (Uttar Pradesh), jute (West Bengal), oilseeds, and pulses are also widely grown on alluvial soils. Statement 3 is wrong: alluvial soils are among the most fertile Indian soils and carry the country's most commercially significant cropping; the claim that they support only subsistence millet inverts the reality.
Sources
- NCERT Class 11 India Physical Environment, Chapter 6 (Soils), pp 70-72
- Indian Council of Agricultural Research (ICAR)
- National Bureau of Soil Survey and Land Use Planning (NBSS&LUP), Nagpur
- ICAR-Indian Institute of Soil Science, Bhopal
- USDA Natural Resources Conservation Service (NRCS) Soil Taxonomy
- Ministry of Agriculture and Farmers Welfare, Soil Health Card
- Wikipedia: Indo-Gangetic Plain
- Wikipedia: Khadir and Bangar
- Wikipedia: Soils of India
Disclaimer
This article is prepared for UPSC preparation by Digitally Learn's editorial team. It covers alluvial soil formation, the Khadar and Bhangar sub-types, distribution, fertility, and crops. Key facts are cross-verified with NCERT and the authoritative sources listed below.
