Soils of India: Types, Degradation and Conservation

1. Soil as a resource: formation and the soil profile

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• Soil is the most important natural resource. It is a living system and the medium in which plants grow. It is the thin upper layer of the Earth's crust (Class 7).
• It forms very slowly. A few cm can take millions of years (Class 10). Class 7 says the process takes from a century to several millennia.
• Formation factors: relief, parent rock (bedrock), climate, vegetation and other life, and time.
• Agents: temperature change, running water, wind, glaciers and decomposers, plus chemical and organic change.
• Steps (Class 7, Fig. 1.8): weathering (rock breaks into particles) → organisms add humus (dark, nutrient-rich organic matter that holds moisture) → a layered soil forms.
• Soil profile: a vertical cut from the surface down to the parent rock. Each layer is a horizon. Mature soils have clear horizons. Young alluvium and mountain soils do not.

Horizon	What it is
O	Leaf litter
A	Topsoil. Rich in humus and full of life. Water washes material down out of it (eluviation)
B	Subsoil. Clay, iron and lime build up here (illuviation)
C	Weathered parent material
R	Bedrock

• Texture: sand (coarse), silt (between sand and clay), clay (finest). Loam is the ideal mix.
• Colour: black comes from titaniferous magnetite and humus. Red comes from iron oxides.
• pH: laterite and peat are acidic. Usar is alkaline.

2. Classifying Indian soils

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• Class 10 says soils are classified by formation factors, colour, thickness, texture, age, and chemical and physical properties. India's varied relief, climate and vegetation produce varied soils.
• Class 7 lists six types: alluvial, black, red, laterite, desert and mountain/alpine. It also mentions the ancient Amarakosha, which names twelve kinds of farmland by fertility.

• Classification of Indian soils (ICAR): after the All India Soil Survey Committee (1953), ICAR recognised eight major groups: 1. Alluvial 2. Black (regur) 3. Red and yellow 4. Laterite 5. Arid (desert) 6. Saline and alkaline 7. Peaty and marshy 8. Forest and mountain

• NBSS&LUP (Nagpur) also maps soils using USDA Soil Taxonomy orders. Vertisols = black soils. Entisols and Inceptisols = alluvium. Alfisols = red soils. Aridisols = desert soils.

• Area order: alluvial is largest (about two-fifths of India), then red, then black (verify proportions).
• Map practice: mark all eight groups on one outline map (Class 10, "India: Major Soil Types"; Class 7, Fig. 1.9).

3. Alluvial soils: khadar and bhangar

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• Alluvial soil is the most widespread and important soil. River sediment builds it up.
• Where:
• the whole Northern Plains, laid down by the Indus, Ganga and Brahmaputra
• a narrow corridor into Rajasthan and Gujarat

• the east-coast deltas of the Mahanadi, Godavari, Krishna and Kaveri

• Grain size: coarse near the break of slope in piedmont plains (Duars, Chos, Terai). Finer further inland.

Bhangar (old alluvium)	Khadar (new alluvium)
Higher terraces, above flood level	Floodplains, renewed by floods every year
More kankar nodules	Finer particles
Less fertile	More fertile

• Kankar: small lumps (nodules) of calcium carbonate. They form in soils of moderate rainfall and are common in bhangar.
• Properties: rich in potash, phosphoric acid and lime. Generally poor in nitrogen and humus, so farmers need fertiliser (beyond NCERT).
• Crops: sugarcane, paddy, wheat, other cereals and pulses. These areas are intensively farmed and densely populated.
• Alluvium in drier areas is more alkaline. It needs treatment and irrigation.

4. Black (regur) soils

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• Black soil is also called regur or black cotton soil, because it is ideal for cotton.
• How it forms: parent rock and climate together. It is typical of the Deccan Trap (basalt) lava region of the northwest Deccan. It matches the Vertisol order.
• Where: plateaus of Maharashtra, Saurashtra, Malwa, Madhya Pradesh and Chhattisgarh. It extends southeast along the Godavari and Krishna valleys. Beyond NCERT, it is also found in parts of Karnataka, Telangana and Tamil Nadu.
• Properties:
• very fine clay that holds moisture well
• rich in calcium carbonate, magnesium, potash and lime

• poor in phosphorus (and, beyond NCERT, in nitrogen and organic matter)

• Self-ploughing of black soil:

• When wet, the clay swells and turns sticky.
• In the hot season it shrinks and develops deep cracks. The cracks let air into the soil.

• It is hard to work when wet, so farmers till it right after the first shower or before the monsoon.

• Crops: cotton, soybean, jowar, groundnut, sugarcane and tur.

• Problems: waterlogging in canal areas. Building foundations crack.

5. Red and yellow soils, and laterite soils

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• Red and yellow soil:
• Formation: develops on crystalline igneous and metamorphic rocks in low-rainfall areas.
• Where: the eastern and southern Deccan. Also Odisha, Chhattisgarh, the southern middle Ganga plain and the Western Ghats piedmont.
• Colour: red comes from iron spread through the rock. It looks yellow where the iron is hydrated (combined with water).
• Properties (beyond NCERT): light and porous. Poor in nitrogen, phosphorus and humus. Productive with fertiliser and irrigation.

• Crops: ragi, groundnut, millets and pulses.

• Laterite soil (Latin later = brick):

• Formation: tropical wet and dry seasons → heavy rain causes intense leaching → silica and bases wash out → iron and aluminium oxides are left behind.
• Properties: deep to very deep and acidic (pH below 6.0). Poor in nutrients. Rich in humus under forest, poor in humus under sparse cover. Erodes easily.
• Where: southern states, the Western Ghats of Maharashtra, Odisha, parts of West Bengal and the Northeast.
• Crops: with conservation in the hills of Karnataka, Kerala and Tamil Nadu, it grows tea and coffee. Red laterite in Tamil Nadu, Andhra Pradesh and Kerala grows cashew.
• It hardens in air and is cut into building bricks.

6. Arid, saline, peaty and forest-mountain soils

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• Arid soil (Class 7 calls it desert soil):
• red to brown, sandy and saline
• In places it is so salty that common salt is made by evaporating its water.
• Heat and fast evaporation leave it with little humus or moisture.
• Kankar fills the lower horizons because calcium increases with depth. This layer blocks water from soaking in.

• With irrigation it can be farmed, as in western Rajasthan (Indira Gandhi Canal).

• Saline and alkaline soils (usar, reh, kallar, thur; beyond NCERT):

• salts of sodium, potassium and magnesium; infertile
• Where: dry areas, the Rann of Kachchh, coastal deltas where seawater gets in, and canal-irrigated Punjab, Haryana and western UP

• Fix: gypsum, drainage and salt-tolerant crops (research at CSSRI, Karnal)

• Peaty and marshy soils:

• heavy rain and poor drainage give high organic matter; black, heavy and acidic

• Where: north Bihar, the Sundarbans, coastal Odisha and Tamil Nadu, and Kerala's Kuttanad (kari soils, where rice is grown below sea level)

• Forest soil:

• loamy and silty on valley sides, coarse on upper slopes
• acidic and low in humus in snowy Himalayan areas
• fertile on river terraces and alluvial fans
• Class 7's alpine soil is "thin, rough and rocky".

7. Soil-crop linkages and nurturing soil fertility

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• Soil-crop links (Class 7, Fig. 1.10):

Soil	Crops
Alluvial	wheat, rice
Black	cotton
Red	millets, groundnut, pulses
Laterite	tea, coffee, cashew
Desert	bajra; other crops only with irrigation
Mountain	temperate fruits

• Kerala grows rice and Punjab grows wheat because of soil, rainfall and irrigation together.
• Nurturing soil (Class 7):
• Traditional: crop rotation, multiple cropping, organic manure (cow dung, panchagavya, beejamrit).

• Modern: terracing, afforestation, ploughing back crop residue, precise use of fertiliser.

• Mulching: covering the soil with residue, leaves or plastic. It keeps in moisture, stops weeds, evens out soil temperature and reduces erosion.

• Nitrogen fixation: Rhizobium bacteria in the root nodules of legumes (pulses) turn nitrogen from the air into soil nitrogen. Soils lose fertility when farmers drop legumes from rice-wheat rotations.
• Soil organic carbon: carbon held in decayed plant and microbe matter. Many Indian soils have less than 0.5 per cent, because of heat, intensive tillage and stubble burning.
• Soil Health Card scheme:
• Launched 19 February 2015 at Suratgarh, Rajasthan.
• Tests 12 parameters: N, P, K, S, Zn, Fe, Cu, Mn, B, pH, EC and organic carbon.
• Gives crop-wise fertiliser advice to correct unbalanced N:P:K use.

• Now part of RKVY (verify current).

• Class 7 also says the Green Revolution impoverished soils over time. Sikkim banned chemical fertilisers and pesticides in 2014 and was declared 100 per cent organic in 2016.

8. Soil erosion: sheet, gully and wind

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• Soil erosion: the soil cover is stripped and washed away (Class 10).
• Soil formation and erosion normally stay in balance.
• Human activity upsets this balance: deforestation, overgrazing, construction and mining.

• The natural agents are water, wind and glaciers.

• Types:

• Sheet erosion: water flows as a sheet down a slope and removes topsoil.
• Rill erosion: small channels form. This is the stage between sheet and gully erosion (beyond NCERT).
• Gully erosion: running water cuts deep channels (gullies) in clayey soils.

• Wind erosion: wind blows loose soil off flat or sloping land. It is common in western Rajasthan and Kachchh.

• Badlands: land so cut up by gullies that it cannot be farmed. In the Chambal basin (Madhya Pradesh, Rajasthan, Uttar Pradesh) these are called ravines. Similar ravines are found along the Yamuna, Mahi and Sabarmati.

• Faulty farming: ploughing up and down a slope makes channels for fast runoff.
• Water erosion hotspots: Himalayan and northeastern slopes under jhum, Western Ghats laterite, and the Shivalik chos of Punjab and Himachal.
• Class 11 lists soil erosion as a terrestrial hazard (Table 6.1). India loses billions of tonnes of soil a year to water erosion (ICAR; verify current).

9. Land degradation: waterlogging, salinity and desertification

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• Soil degradation: soil quality and output fall because of erosion, loss of nutrients and organic matter, salinity, waterlogging and chemical pollution.
• Main causes by region (Class 10):

Cause	States
Mining (deforestation, pits, overburden)	Jharkhand, Chhattisgarh, MP, Odisha
Overgrazing	Gujarat, Rajasthan, MP, Maharashtra
Over-irrigation	Punjab, Haryana, western UP

• Mineral dust also harms land. Grinding limestone (for cement) and calcite and soapstone (for ceramics) makes dust that settles and stops water soaking in. Industrial effluents pollute land and water.
• Waterlogging and salinisation:
• Over-irrigation and seepage from unlined canals raise the water table into the root zone. This is waterlogging.
• Water rises to the surface through capillary action and evaporates.
• Salts are left behind (salinisation). Sodium carbonate makes the soil alkaline (alkalisation).

• Examples: the Indira Gandhi Canal command, Punjab and Haryana.

• ISRO-SAC Atlas (2021): about 97.85 million ha, roughly 30 per cent of India, was degraded in 2018-19. Water erosion was the biggest process.

• UN Convention to Combat Desertification:
• adopted 17 June 1994 in Paris; came into force in 1996
• India hosted COP14 at Greater Noida in September 2019
• India pledged to restore 26 million ha of degraded land by 2030 and to reach land degradation neutrality

10. Soil conservation: methods by terrain

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• Soil conservation means managing soil so it does not erode or degrade and stays fertile.
• Class 10 methods:
• Contour ploughing: ploughing along contour lines, across the slope, slows the water.
• Terrace farming: steps are cut into slopes to make flat fields. It is well developed in the western and central Himalayas, for example Uttarakhand. Class 11 recommends it instead of jhum in the Northeast, to reduce landslides.
• Strip cropping: large fields are split into strips, with grass strips between the crops. This breaks the force of wind.

• Shelter belt: rows of trees that act as windbreaks. They have helped stabilise sand dunes and the desert in western India.

• Beyond NCERT:

• Contour bunding: earthen embankments along the contours of sloping fields, common in Deccan dryland farming.
• Continuous contour trench: trenches along hill contours that slow, hold and soak in rainwater (Ralegan Siddhi, Hiware Bazar).
• Programmes: PMKSY-Watershed Development, National Mission for Sustainable Agriculture (verify current).

Terrain	Main measures
Hills	terracing, contour ploughing, trenches, afforestation
Plateaus and drylands	contour bunding, check dams, mulching
Deserts	shelter belts, fixing dunes with thorny bushes, grazing control
Canal commands	drainage, canal lining, gypsum
Ravines	gully plugging, plantation
Mining areas	mining control, treatment of effluents

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Exam angles

Prelims — high-yield facts and traps

• Parent material → soil:
• Deccan basalt → black soil
• crystalline igneous rock → red soil
• leaching in the wet-dry tropics → laterite

• Himalayan rivers and east-coast deltas → alluvium

• Khadar is new, fertile floodplain soil. Bhangar is old, higher, kankar-rich soil. Trap: "Bhangar is more fertile than khadar" is FALSE.

• Black soil:
• rich in lime, magnesium, potash and calcium carbonate
• poor in phosphorus
• self-ploughing; grows cotton

• Trap: "Black soil is rich in phosphorus" is FALSE.

• Laterite is acidic (pH below 6), leached and brick-like. With conservation it grows tea, coffee and cashew.

• Arid soil has kankar in its lower horizons, which blocks infiltration. It can be farmed with irrigation in western Rajasthan.
• ICAR has 8 groups (including saline and peaty: Kuttanad, Sundarbans). Class 7 lists 6 types.
• Erosion sequence: sheet → rill → gully → badland. Chambal badlands are called ravines.
• Method–purpose matching:
• contour ploughing → slopes
• terracing → Uttarakhand and Himalayas
• strip cropping and shelter belts → wind

• contour bunding → drylands

• Soil Health Card: launched 2015 at Suratgarh; tests 12 parameters.

• UNCCD: 1994. India hosted COP14 in 2019. India's target: 26 million ha restored by 2030.
• Main cause of land degradation by state:
• Punjab → over-irrigation (Class 10 exercise)
• Jharkhand → mining
• Rajasthan and Gujarat → overgrazing

Mains — GS-I themes

1. Explain how parent rock and climate together produce India's major soil types. Support the answer with a map.
2. Land degradation in India: give its regional causes and a conservation strategy suited to each region.
3. The Green Revolution and soil health: waterlogging, salinity, NPK imbalance and falling organic carbon. Can the Soil Health Card and natural farming fix these problems?
4. Soil erosion in the Himalayas and the Chambal ravines: causes, effects and remedies.
5. Desertification and land degradation neutrality: how far has India progressed on its UNCCD pledge?

Current-affairs hooks

• New editions of the ISRO-SAC land degradation atlas and UNCCD reports (verify current).
• Soil Health Card coverage, fertiliser subsidy reform, nano urea and natural farming missions (verify current).
• Stubble burning in Punjab-Haryana and its effect on soil organic carbon.
• World Soil Day (5 December) and Desertification and Drought Day (17 June) themes.
• Salinity in the Indira Gandhi Canal command, and seawater intrusion on the coast after cyclones.