Chapter 13 · 20 min read
Indian Soils
What is Soil?
- Soil = the thin top layer of the Earth's crust comprising rock particles mixed with organic matter — a complex natural resource that sustains life by supporting plant growth, regulating water flow, and providing habitat for organisms.
- Pedology = the scientific study of soils in their natural environment.
- Pedogenesis = the natural process of soil formation — includes weathering, leaching, calcification, humification, and other processes acting over thousands to millions of years.
Soil Texture — Basic Types
Classified by the proportion of particles of various sizes:
| Type | Dominant Particle | Key Property |
|---|---|---|
| Sandy | Large particles (0.05–2 mm) | Drains quickly; light-coloured; low organic matter; dry; well-aerated |
| Clayey | Fine particles (<0.002 mm) | Holds water tightly; little air; heavy; high water retention |
| Loamy | Mix of sand, clay, silt | Best for farming — right drainage + water-holding capacity |
| Silty | Medium particles (0.002–0.05 mm) | Deposited in riverbeds; very fertile; smooth texture |
- Ideal agricultural topsoil = Loam — balanced mix of sand, clay, and silt, with humus.
- Humus = dark organic matter from decayed plant/animal remains; holds water + nutrients; acts as natural fertiliser.
Crop–Soil Texture Preference
| Crop | Preferred Soil |
|---|---|
| Paddy (Rice) | Clayey + rich organic matter; high water retention |
| Wheat, Gram | Clayey or loamy |
| Cotton | Sandy loam or loam; good drainage + aeration |
| Lentils/Pulses | Loamy soils with easy drainage |
Soil Profile (Soil Horizons)
A vertical section through soil layers is called the soil profile. Each layer = a horizon, distinguished by colour, texture, depth, and chemical composition.
| Horizon | Name | Description |
|---|---|---|
| O | Organic layer | Dominated by organic material — undecomposed or partially decomposed litter (leaves, twigs, needles, mosses). Present above mineral soil. |
| A | Topsoil / Surface soil | Organic matter mixed with minerals; dark colour due to high organic content; richest in life; layer of eluviation (loss of clay, iron, aluminium downward) |
| E | Eluviation layer | Significantly leached of clay, iron, and aluminium oxides; concentration of resistant minerals (quartz) left behind; lighter colour; found in older well-developed soils between A and B |
| B | Subsoil | Zone of illuviation — accumulates clay, iron, aluminium, organic compounds leached from above; higher clay content than A horizon; harder and more compact |
| C | Parent material | Large, unbroken rock fragments; weathered parent material; transition between soil and bedrock; accumulates soluble inorganic compounds |
| R | Bedrock | Continuous hard rock masses; the ultimate foundation for soil; not part of true soil profile |
Eluviation = movement of minerals OUT of a horizon (downward by percolating water). Illuviation = accumulation of minerals IN a horizon (deposited from above).
Factors Influencing Soil Formation in India
| Factor | Role |
|---|---|
| Parent Material | Determines colouration, mineral composition, texture of initial soil |
| Relief | Steep slopes → erosion, thin soils; gentle slopes/plains → deep, fertile soils |
| Climate | Temperature + rainfall determine weathering intensity, water percolation, micro-organisms |
| Natural Vegetation | Adds organic matter (humus); protects from erosion; influences soil moisture |
| Time | Longer weathering → more mature soils (peninsular soils more mature than alluvial soils) |
Parent Material Categories in India
| Type | Description | Soil Formed |
|---|---|---|
| Ancient crystalline and metamorphic rocks | Oldest (Pre-Cambrian, ~4 billion years); granites, gneisses, schists; form 'Basement Complex' of Peninsular India; rich in ferromagnesium minerals | Red soils (iron oxide released on weathering) |
| Cuddapah and Vindhyan rocks | Ancient sedimentary rocks (4,000 m thick) | Calcareous (calcium carbonate) + argillaceous (clay) soils; devoid of metalliferous minerals |
| Gondwana rocks | Younger sedimentary rocks | Comparatively less mature soils; low fertility; fairly uniform |
| Deccan Basalts | Volcanic rocks (Deccan Traps); rich in titanium, magnetite, aluminium, magnesium | Black cotton soils (regur) — dark colour due to titaniferous magnetite |
| Tertiary + Mesozoic sedimentary rocks | Younger rocks of extra-peninsular India (plains + Himalayas) | Immature alluvial soils; high porosity; little relation to parent rock |
| Recent and sub-recent deposits | River-deposited material (Quaternary) | Recent alluvial soils; most fertile |
Climate → Soil Colour Relationship (Important!)
| Climate Condition | Soil Type | Why |
|---|---|---|
| High rainfall + high temperature | Red / Laterite | Iron + aluminium oxides concentrated at surface by alternating leaching (wet) and capillary rise (dry); silica leached away |
| Low rainfall + high temp (arid/semi-arid) | Light-coloured soils | Evaporation > precipitation; little humus; pedocal (lime-accumulating) soils |
| Hot summer + low rainfall (Tamil Nadu) | Black soils | Even on non-basaltic parent rock; climatic conditions create similar regur-type soil |
| Arid climate (Rajasthan) | Sandy soils | Both granite and sandstone produce sandy soil under arid conditions — climate overrides parent rock |
| Alternate wet + dry (tropical) | Laterite | Leaching + capillary action alternately → iron/aluminium baking into brick-hard surface |
Peninsular vs. Extra-Peninsular Soils
| Feature | Peninsular Soils | Extra-Peninsular (Alluvial) Soils |
|---|---|---|
| Formation | In situ — from underlying bedrock directly | Transported and deposited by rivers and wind |
| Type | Sedentary / Residual soils | Transported / Azonal soils |
| Maturity | More mature | Less mature (recent origin) |
| Fertility | Generally less fertile (coarse-grained) | Highly fertile (fine silt + clay replenished by floods) |
| Depth | Generally shallow | Very deep |
Major Soil Groups of India
Standard UPSC classification (ICAR-NBSS&LUP, based on NCERT): 8 major groups.
| # | Soil Type | Area (lakh km²) | % of India |
|---|---|---|---|
| 1 | Alluvial | ~15.0 | 45.6% |
| 2 | Black (Regur) | 5.46 | 16.6% |
| 3 | Red | ~3.5 | 10.6% |
| 4 | Laterite/Lateritic | 2.48 | 7.5% |
| 5 | Forest/Mountain | 2.85 | 8.67% |
| 6 | Arid/Desert | 1.42 | 4.32% |
| 7 | Saline/Alkaline | ~0.68 | ~2.07% |
| 8 | Peaty/Marshy | <0.22 | <0.67% |
1. Alluvial Soils
Largest soil group in India — covers ~45.6% of total land area.
Formation
- Formed mainly by silt deposited by Indo-Gangetic-Brahmaputra rivers — classic transported/azonal soils.
- Parent material: Rocks of the Himalayas, eroded and carried downstream.
- In coastal regions: formed by wave action and river delta deposition.
Characteristics
- Immature with weak profiles due to recent origin.
- Mostly loamy; sandy and clayey also occur.
- Porous — loamy nature gives good drainage + aeration.
- Recurrently replenished by floods — explains sustained fertility.
- Pebbly/gravelly soils rare.
- Kankar (calcareous concretions) beds present in some river terraces.
Chemical Properties
| Property | Status |
|---|---|
| Nitrogen | Low |
| Potash, Phosphoric acid, Alkalis (lime) | Adequate |
| Iron oxide and lime | Variable (widely) |
| Humus | Variable; generally moderate |
Distribution
- Indo-Gangetic-Brahmaputra plains (Punjab → UP → Bihar → Bengal → Assam) — except where covered by desert sand.
- Deltas of Mahanadi, Godavari, Krishna, Cauvery — called deltaic alluvium or coastal alluvium.
- Narmada and Tapti valleys and northern Gujarat.
Geological Sub-types (Critical for UPSC)
| Sub-type | Description | Characteristics |
|---|---|---|
| Khadar | New / Younger alluvium — deposited by recent floods; closer to river channels | Light-coloured; fine texture; renewed every flood season; more fertile |
| Bhangar | Old / Older alluvium — above flood level; terrace deposits | Darker; coarser; contains Kankar nodules; less frequently replenished |
Crops in Alluvial Soils
Rice, wheat, sugarcane, tobacco, cotton, jute, maize, oilseeds — most productive agricultural soils of India; support >40% of India's population.
2. Black Soils (Regur / Black Cotton Soil)
Best known for cotton cultivation — also called regur.
Formation
- Primary parent material: Deccan basalts (volcanic rocks) — Deccan Traps formed by fissure volcanic eruptions.
- In Tamil Nadu: gneisses and schists are parent material (climate effect dominates over parent rock).
- Characteristic of hot temperatures + low rainfall — typical of dry/hot peninsular regions.
Characteristics
- Highly argillaceous — clay factor >62%; extremely high water retention.
- In summer: cracks deeply (broad, deep cracks) → lower layers retain moisture; oxygenation down to depth.
- In rainy season: swells greatly → becomes very sticky; ploughing becomes difficult.
- Upland black soils = low fertility; valley black soils = very fertile.
- Has been used for centuries for cotton without manure — very slow exhaustion rate.
Colour
- Black due to presence of titaniferous magnetite (titanium + iron compound) in parent Deccan basalt.
- In Tamil Nadu/AP: black colour from crystalline schists and basic gneisses.
Chemical Composition
| Constituent | Percentage |
|---|---|
| Alumina | ~10% |
| Iron oxide | ~10% |
| Lime + Magnesium carbonates | 6–8% |
| Potash | <0.5% (variable) |
| Phosphates, Nitrogen, Humus | Low |
Distribution
- 5.46 lakh km² (16.6% of India) — Maharashtra (largest single block), Madhya Pradesh, parts of Karnataka, Telangana, Andhra Pradesh, Gujarat, Tamil Nadu.
Crops
Cotton (primary), wheat, jowar, linseed, Virginia tobacco, castor, sunflower, millets; rice + sugarcane where irrigation available.
[UPSC Prelims 2021] Black cotton soil of India has been formed due to weathering of: a) Brown forest soil b) Fissure volcanic rock c) Granite and schist d) Shale and limestone Answer: b) ✓ — Deccan Traps (fissure volcanic eruption) is the primary parent material. Tamil Nadu is the exception (gneisses/schists), but the correct general answer is fissure volcanic rock.
3. Red Soils
Second most widespread soil type; acidic and poor in nutrients.
Formation
- Parent rocks: crystalline and metamorphic rocks — acid granites, gneisses, quartzites.
- Formed in regions of low rainfall where leaching is limited.
- Ancient pre-Cambrian basement rocks → iron oxide released on weathering → red colour.
Characteristics
- Texture varies from sand to clay; majority loamy.
- Uplands: poor, gravelly, porous (shallow soil + intense erosion).
- Lowlands/valleys: rich, deep, dark, fertile.
- Cannot retain water like black soils.
Colour
- Red due to iron oxide (ferric oxide / Fe₂O₃).
- Red colour is more due to wide diffusion (dispersal throughout) of iron oxide, not high concentration.
Chemical Properties
- Acidic (acidic parent rocks).
- Poor in: lime, magnesia, phosphates, nitrogen, humus.
- Fairly rich in: potash and potassium.
Distribution
- 3.5 lakh km² (10.6%): almost all of Tamil Nadu, parts of Karnataka, SE Maharashtra, Telangana, AP, MP, Chhattisgarh, Odisha, Chota Nagpur plateau, south Bihar, West Bengal, UP, Aravallis, eastern Rajasthan (Mewar/Marwar Plateau), parts of Northeast states.
Crops
With proper fertilisers + irrigation: cotton, wheat, rice, pulses, millets, tobacco, oilseeds, potatoes, fruits.
[UPSC Prelims 2010] Red soil colour is mainly due to: a) Abundance of magnesium b) Accumulated humus c) Presence of ferric oxide d) Abundance of phosphates Answer: c) ✓ — Fe₂O₃ (iron III oxide / haematite) gives the characteristic red/reddish-brown colour.
4. Laterite and Lateritic Soils
End-products of intense tropical weathering — ironically infertile despite heavy rainfall areas.
Formation
- Formed under high temperature + heavy rainfall with alternating wet and dry periods.
- Heavy rain → leaching (lime and silica washed away) → residue of iron and aluminium oxides (sesquioxides).
- In dry season: evaporation + capillary action brings iron/aluminium oxides to surface → baked hard.
- Name: "Laterite" from Latin later = brick — hardens on losing moisture; can literally be cut into bricks.
Chemical Composition
- Rich in: Bauxite (aluminium oxide), ferric oxides.
- Very poor in: Lime, magnesia, potash, nitrogen.
- Sometimes: High phosphate content (as iron phosphate).
- In wetter areas: higher humus content.
Characteristics
- Red in colour; little clay, more gravel of red sandstone.
- Hardens greatly on drying — once hardened, durable as building material (historic use in Kerala, Karnataka temples, Portuguese churches, and colonial buildings).
- Cannot be further weathered once laterised.
Distribution
- 2.48 lakh km² (7.5%) — continuous stretches on summits of Western Ghats (1,000–1,500 m), Eastern Ghats, Rajmahal Hills, Vindhyan and Satpura ranges, Malwa Plateau.
- Also: south Maharashtra, Karnataka, and scattered other regions.
Crops
- Too leached for most crops; low fertility.
- With manuring + irrigation: tea, coffee, rubber, cinchona, coconut, arecanut (plantation crops adapted to acidic, well-drained laterite).
- Some areas support grazing grounds and scrub forests.
[UPSC Prelims 2013] Which statements about laterite soils are correct?
- Generally red in colour ✓
- Rich in nitrogen and potash ✗ (very poor in these)
- Well-developed in Rajasthan and UP ✗ (developed in W Ghats, E Ghats, Rajmahal Hills)
- Tapioca and cashew nuts grow well ✓ (tolerant of acidic, low-nutrient soils; deep roots) Answer: c) 1 and 4 ✓
5. Forest and Mountain Soils
Formation
- Formation governed by characteristic deposition of organic matter from forest cover.
- Highly heterogeneous — character changes with parent rock, ground configuration, organic decomposition, mineral weathering, and climate.
- Can differ greatly even in close proximity.
Distribution
- 2.85 lakh km² (8.67%) — Himalayan valleys and less steep/north-facing slopes (south-facing slopes too steep for soil retention); Western and Eastern Ghats.
- South-facing Himalayan slopes: very steep, heavily eroded → minimal soil development.
Chemical Properties
- Very rich in humus (thick forest litter).
- Deficient in: potash, phosphorus, lime.
- Need considerable fertilisers for good yields.
Crops
| Region | Crops |
|---|---|
| Peninsular hills (W/E Ghats) | Tea, coffee, spices, tropical fruits |
| Himalayan forest region | Wheat, maize, barley, temperate fruits (apple, pear, plum) |
6. Arid and Desert Soils
Composition and Formation
- Aeolian sand (90–95%) + clay (5–10%); formed under wind action in arid zones.
- Cover 1.42 lakh km² (4.32%).
- Desertification of neighbouring soils common due to intrusion of aeolian (wind-blown) sand.
Distribution
- Arid/semi-arid Rajasthan, Punjab, Haryana — sand blown from Indus basin + coast by SW monsoon winds.
- Sandy soils (without clay) also in coastal regions of Odisha, Tamil Nadu, Kerala.
Chemical Properties
| Property | Status |
|---|---|
| Organic matter | Poor |
| Calcium carbonate | Present (alkaline tendencies) |
| Calcium gradient | Increases downwards; subsoil has 10× more calcium than topsoil |
| Phosphate content | As high as normal alluvial soils |
| Nitrogen | Low, but some available as nitrates |
Crops
- Drought-resistant + salt-tolerant crops: barley, cotton, millets, maize, pulses.
- Phosphates + nitrates make these soils fertile wherever moisture is available — reclamation with irrigation possible.
7. Saline and Alkaline Soils
Formation
Two main processes:
- Poor drainage + waterlogging — water with high salt concentration stagnates; salts deposited in topsoil after evaporation.
- High sub-soil water table + capillary rise — during dry season, capillary action brings salt-laden water from below to surface; water evaporates; salts remain → infertile crust.
Also: in coastal areas, storm surges during cyclones push saline sea water inland → soil contamination.
Distribution
- ~68,000 km² (2.07%) — canal-irrigated areas and high sub-soil water table areas.
- States affected: Andhra Pradesh, Telangana, Karnataka, Bihar, Uttar Pradesh, Haryana, Punjab (excess irrigation side-effect), Rajasthan, Maharashtra.
- Gujarat: Gulf of Khambhat — tidal saline deposits; estuaries of Narmada, Tapi, Mahi, Sabarmati affected.
- Coastal AP and Tamil Nadu: cyclone storm surges cause periodic soil salinisation.
Why Excess Irrigation Causes Saline Soils
Excess water → raises the sub-soil water table → during dry season, capillary action brings salt-laden groundwater to surface → evaporation leaves salt crust → waterlogging + soil salinity (common in canal-commanded areas of Punjab and Haryana).
8. Peaty and Marshy Soils
Characteristics
- Large amount of organic matter + considerable soluble salts.
- Black, heavy, highly acidic.
- Most humid regions of India.
- Most are waterlogged during rainy season; drained and used for paddy cultivation after monsoon.
- Deficient in: potash and phosphate.
Distribution
- Kottayam and Alappuzha districts of Kerala (kuttanad — below sea-level paddy cultivation).
- Coastal Odisha and Tamil Nadu.
- Sundarbans of West Bengal.
- Bihar (Mithila region).
- Almora district, Uttarakhand.
Soil Degradation in India
Scale of the Problem (Latest Data)
| Metric | Value | Source |
|---|---|---|
| Total degraded land | 97.85 million ha (29.7%) of India's geographical area | SAC/ISRO Land Degradation Atlas, 2021 |
| Desertification | 83.69 million ha (2018–19) — up from 81.48 Mha (2003–05) | MoEFCC |
| Water erosion | 11.01% of land | SAC 2021 |
| Vegetation degradation | 9.15% | SAC 2021 |
| Wind erosion | 5.46% | SAC 2021 |
| Flooding/waterlogging | ~14 million ha | Estimates |
| Soil acidification | ~16 million ha | Estimates |
Causes of Soil Degradation
| Cause | Mechanism |
|---|---|
| Water erosion | Heavy monsoon rainfall on bare/deforested slopes; rills and gullies; Chambal ravines, NE hill slopes |
| Wind erosion | Thar desert; aeolian sand movement |
| Waterlogging + salinisation | Excess irrigation raises water table; capillary salt rise |
| Desertification | Encroachment of aeolian sand into semi-arid zones |
| Jhum (shifting) cultivation | NE India — clears forest patches, leaves soil exposed |
| Mining and construction | Topsoil stripping in mineral-rich regions (Chota Nagpur, Odisha) |
| Overgrazing | Destroys vegetation cover → erosion |
| Chemical degradation | Excessive chemical fertilisers → soil acidification, nutrient imbalance |
Soil Conservation and Government Initiatives
India's Land Degradation Neutrality (LDN) Target
- India pledged at UNCCD COP to restore 26 million hectares of degraded land by 2030 (Bonn Challenge commitment).
- Progress: ~18.94 million ha already restored (as per last available data).
- LDN principle: any new degradation to be balanced by equal restoration elsewhere → net zero land degradation.
Soil Health Card (SHC) Scheme
| Detail | Value |
|---|---|
| Launched | 19 February 2015 at Suratgarh, Rajasthan — by PM Modi |
| 10th Anniversary | February 2025 |
| Type | Centrally Sponsored Scheme (Ministry of Agriculture) |
| Purpose | Issue soil health cards to every farmer — tests 12 parameters (N, P, K, pH, organic carbon, S, Zn, B, Fe, Mn, Cu, EC) |
| Cycle | Every 2 years |
| Village labs (Feb 2025) | 665 village-level soil testing labs in 17 states |
| School labs | 1,000+ soil testing labs in schools |
| Outcome | Enables farmers to apply precise fertiliser doses → reduces over-application → saves money + prevents soil damage |
Other Key Programmes
| Programme | Focus |
|---|---|
| Pradhan Mantri Krishi Sinchayee Yojana (PMKSY) | Efficient irrigation (drip/sprinkler) → reduces waterlogging and salinity |
| National Action Programme to Combat Desertification (NAPCD) | Address desertification in arid/semi-arid zones |
| Watershed Development (IWMP) | Integrated watershed management — check soil erosion |
| Green India Mission | Increasing forest/tree cover → reduces water erosion |
| PM PRANAM scheme | Promote alternative fertilisers → reduce chemical load on soils |
UPSC Corner
Key One-Liners for Prelims
- Largest soil group: Alluvial soils — ~45.6% of India — support >40% of population
- Alluvial soils = transported/azonal soils; peninsular soils = sedentary/residual soils
- Khadar = new alluvium (closer to river, flooded often, more fertile); Bhangar = old alluvium (terrace, Kankar nodules, less fertile)
- Black soil = parent material is Deccan basalt (fissure volcanic rocks); clay >62%; cracks in summer; best for cotton
- Black soil colour = due to titaniferous magnetite (iron-titanium compound in parent Deccan basalt)
- Regur = another name for black cotton soil; also called cotton soil
- Red soil colour = ferric oxide (Fe₂O₃) — wide diffusion, not concentration
- Laterite = Latin for brick; formed by alternating wet-dry leaching; hardens on drying
- Laterite rich in: bauxite + ferric oxides; poor in: lime, magnesia, potash, nitrogen
- Laterite formation requires: high rainfall + high temperature + alternating wet and dry
- Peaty soils = acidic + rich organic matter; found in Kottayam/Alappuzha (Kerala), Sundarbans (WB)
- Saline soils = caused by: poor drainage, excess irrigation, high water table + capillary rise, cyclone storm surges
- India's degraded land = ~97.85 million ha (29.7%) — SAC/ISRO 2021 assessment
- India's LDN restoration target = 26 million ha by 2030 (Bonn Challenge)
- Soil Health Card Scheme launched: 19 February 2015, Suratgarh, Rajasthan; 10th anniversary February 2025
Mains GS1/GS3 Questions
- "Describe the distribution of alluvial soils in India. How does the Khadar-Bhangar division determine agricultural potential?" [GS1 type]
- "What are laterite soils? Explain their formation and why they are unsuitable for conventional agriculture despite forming in high-rainfall areas." [GS1 type]
- "Soil degradation is a serious environmental and food security challenge in India. Discuss its causes, extent, and the government's measures to address it." [GS3 type]
- "Examine the factors responsible for the formation and characteristics of black cotton soils. How do these soils support agriculture in the Deccan plateau?" [GS1 type]
MCQ Trap Awareness
- Trap: "Black soil is formed from granite and schist" → Partially wrong — Deccan basalt (fissure volcanic rock) is the primary parent material; Tamil Nadu is an exception where gneisses/schists can form black soil under hot+dry climate.
- Trap: "Red soil is red due to high iron content" → Wrong — red colour is due to wide diffusion of ferric oxide, not necessarily high iron percentage.
- Trap: "Laterite soils are fertile because of high rainfall" → Wrong — heavy rainfall causes leaching, making them infertile despite forming in high-rainfall zones.
- Trap: "Laterite soils are found mainly in Rajasthan and UP" → Wrong — found in W Ghats, E Ghats, Rajmahal Hills; Rajasthan has desert/arid soils.
- Trap: "Khadar is older alluvium" → Wrong — Khadar = new/younger alluvium; Bhangar = old alluvium.
- Trap: "Alluvial soils are sedentary soils" → Wrong — alluvial soils are transported/azonal soils; peninsular soils are sedentary.
- Trap: "Black soils crack during rainy season" → Wrong — black soils crack during the dry/summer season when moisture evaporates; they swell and become sticky in rainy season.
- Trap: "India's soil degradation is 147 million ha" → Use 97.85 million ha (SAC 2021) for the most official cited figure; 147 Mha is an older estimate from different sources with broader degradation definitions.
- Trap: "Saline soils occur only in coastal areas" → Wrong — they extensively occur in canal-irrigated areas (Punjab, Haryana, UP) due to excess irrigation and waterlogging.
- Trap: "Peaty soils are deficient in nitrogen" → Wrong — peaty soils are rich in organic matter (but deficient in potash and phosphate).
Key Facts(24 of 113)
Soil = the thin top layer of the Earth's crust comprising rock particles mixed with organic matter — a complex natural resource that sustains life by supporting plant growth, regulating water flow, and providing habitat for organisms.
Pedology = the scientific study of soils in their natural environment.
Pedogenesis = the natural process of soil formation — includes weathering, leaching, calcification, humification, and other processes acting over thousands to millions of years.
Ideal agricultural topsoil = Loam — balanced mix of sand, clay, and silt, with humus.
Humus = dark organic matter from decayed plant/animal remains; holds water + nutrients; acts as natural fertiliser.
Formed mainly by silt deposited by Indo-Gangetic-Brahmaputra rivers — classic transported/azonal soils.
Parent material: Rocks of the Himalayas, eroded and carried downstream.
In coastal regions: formed by wave action and river delta deposition.
Immature with weak profiles due to recent origin.
Mostly loamy; sandy and clayey also occur.
Porous — loamy nature gives good drainage + aeration.
Recurrently replenished by floods — explains sustained fertility.
Kankar (calcareous concretions) beds present in some river terraces.
Indo-Gangetic-Brahmaputra plains (Punjab → UP → Bihar → Bengal → Assam) — except where covered by desert sand.
Deltas of Mahanadi, Godavari, Krishna, Cauvery — called deltaic alluvium or coastal alluvium.
Narmada and Tapti valleys and northern Gujarat.
Primary parent material: Deccan basalts (volcanic rocks) — Deccan Traps formed by fissure volcanic eruptions.
Characteristic of hot temperatures + low rainfall — typical of dry/hot peninsular regions.
Highly argillaceous — clay factor >62%; extremely high water retention.
In summer: cracks deeply (broad, deep cracks) → lower layers retain moisture; oxygenation down to depth.
In rainy season: swells greatly → becomes very sticky; ploughing becomes difficult.
Upland black soils = low fertility; valley black soils = very fertile.
Black due to presence of titaniferous magnetite (titanium + iron compound) in parent Deccan basalt.
5.46 lakh km² (16.6% of India) — Maharashtra (largest single block), Madhya Pradesh, parts of Karnataka, Telangana, Andhra Pradesh, Gujarat, Tamil Nadu.