Soils

Why this chapter matters for UPSC: Soils was Chapter 6 of India: Physical Environment until NCERT's rationalisation. It is not in the current reprint (2026-27), whose six chapters end with Natural Hazards and Disasters. This page follows the pre-rationalised text (2021-22 reprint) and adds the soil section of the current Class 10 book (Contemporary India II, Chapter 1), which still covers Indian soils. Soils come up in Prelims as soil-to-region and soil-to-crop matching, and in Mains through resources, land degradation and conservation.

Contemporary hook: The Soil Health Card Scheme completed ten years on 19 February 2025. By then 24.74 crore cards had been generated (PIB, 4 Feb 2025), and the count reached 26.09 crore by July 2026 (Lok Sabha answer, 21 Jul 2026). Since 2022-23 the scheme has run as the "Soil Health & Fertility" component of the Rashtriya Krishi Vikas Yojana (PIB, 19 Feb 2025).

🧠 First Principles — Read This First

Soil is the loose layer on the land surface. It is a mixture of rock particles, decayed plant and animal matter (humus), water and air. Plants take water and nutrients from it, and most of our food grows in it.

Soil forms when weathering breaks down a parent rock and living things add organic matter. NCERT names five controlling factors: relief, parent material, climate, vegetation and other life-forms, and time. Human activity is a sixth influence. The process is slow. The Class 11 text says soil has "evolved over thousands of years", and the Class 10 text says it takes "millions of years" to build a few centimetres. Either way, soil lost to erosion is not replaced within a human lifetime.

Two ideas explain most of the chapter. The first is that the parent material sets the starting chemistry. Basalt lava weathers into clay-rich black soil, old crystalline rocks give red soil, and river sediment gives alluvium. The second is that climate decides what happens to that material. Heavy tropical rain washes away lime and silica and leaves iron and aluminium behind, which produces laterite. In a dry climate, evaporation pulls salts to the surface and leaves sandy, saline arid soil.

Picture two pots of the same garden soil, one left in a dry corner and one watered every day for years. Their soils end up different, and the same thing happens across India's regions.

Three ideas carry the chapter: soil forms from parent rock under climate and time, so each soil group belongs to a region; fertility is partly natural and partly made by people; and the same irrigation that raised yields can ruin the soil.

PART 1 — Quick Reference

Table 1: Factors of soil formation (NCERT)

Source: NCERT, India: Physical Environment, Class 11, Ch. 6 "Soils" (2021-22 reprint).

Table 2: The soil profile (NCERT)

Source: NCERT Class 11 IPE, Ch. 6 (2021-22). NCERT describes three horizons above the bedrock. The O (litter) and R (bedrock) labels used in soil-science textbooks are not part of the NCERT scheme.

Table 3: ICAR classification of Indian soils by USDA Soil Taxonomy order

Source: Soils of India, National Bureau of Soil Survey and Land Use Planning (NBSS&LUP, ICAR), Publication No. 94, as printed in NCERT Class 11 IPE, Ch. 6 (2021-22 reprint, archived copy). The table lists seven orders plus "Others". Inceptisols are the largest order, not Vertisols (the black-soil order).

Table 4: The eight soil groups (NCERT: classified "on the basis of genesis, colour, composition and location")

Sources: NCERT Class 11 IPE, Ch. 6 (2021-22); NCERT Class 10 Contemporary India II, Ch. 1 "Resources and Development" (Reprint 2026-27). Areas in hectares for these eight groups are not given here: NCERT gives only the alluvial share (about 40%), and no single official table of group-wise areas was found to cite.

Table 5: How much of India's land is degraded? Two official figures

The two official figures measure different things and should not be compared as a trend. NBSS&LUP mapped soil degradation by type, while ISRO-SAC mapped land degradation and desertification processes from satellite data. Against India's total geographical area of 328.7 Mha (Bhattacharyya et al. 2015), 97.84 Mha works out to about 29.8%. That percentage is arithmetic on the two cited figures, not a published number.

PART 2 — Concepts & Narrative

How Indian soils came to be classified

People have long grouped soils by how they look and how well they grow crops. NCERT traces the history in three steps:

• Ancient period. Soils were classified as urvara (fertile) and usara (sterile).
• 16th century. Classification used inherent characteristics and external features: texture (sandy, clayey, silty, loam), colour (red, yellow, black), slope and moisture.
• After Independence. The Soil Survey of India (established 1956) surveyed selected areas such as the Damodar Valley. The National Bureau of Soil Survey and Land Use Planning, an ICAR institute, then classified Indian soils according to the USDA Soil Taxonomy so that they could be compared internationally (Table 3).

The eight-group list in Table 4 is a separate scheme based on genesis, colour, composition and location. Prelims questions can use either vocabulary. "Vertisols" are the black soils, and "Aridisols" broadly correspond to the arid soils.

Alluvial soils

Rivers carry and deposit alluvial soil rather than forming it from the rock underneath. NCERT puts its extent at about 40% of the country. That makes it the most widespread group by NCERT's genesis classification, and Class 10 calls it "the most widely spread and important soil". Its character changes in three ways:

• Texture changes downstream. It is coarse near the break of slope in piedmont plains (Class 10 names the Duars, Chos and Terai), becomes more loamy and clayey in the lower and middle Ganga plain and the Brahmaputra valley, and its sand content falls from west to east.
• Colour depends on depth, texture and age. It ranges from light grey to ash grey.
• Chemistry. Class 11 calls it generally rich in potash and poor in phosphorus. Class 10 says it contains "adequate proportion of potash, phosphoric acid and lime". The two books disagree on phosphorus. For a Class 11-based answer, use "rich in potash, poor in phosphorus".

The Class 10 book adds that in drier areas alluvial soils are more alkaline and can be made productive with treatment and irrigation. Alluvial regions are intensively cultivated and densely populated.

Red, yellow and laterite soils: the colour of iron

Red and laterite soils both owe their colour to iron, but they form in different ways.

• Red soil. Iron is spread through crystalline and metamorphic rocks. When those rocks weather, mostly in low-rainfall parts of the eastern and southern Deccan, the iron gives a red colour. Where the iron is hydrated, the soil turns yellow. Fertility depends on texture: fine-grained red soil is normally fertile, while coarse upland red soil is poor.
• Laterite. Laterite forms through leaching. Under high temperature and heavy rain, water removes lime and silica and leaves iron oxide and aluminium compounds. Bacteria that thrive in the heat also break down humus quickly. The result is poor in organic matter, nitrogen, phosphate and calcium, with excess iron oxide and potash. Class 11 says laterites are "not suitable for cultivation" without manures and fertilisers. Class 10 says laterite develops under an alternation of wet and dry seasons and is acidic (pH below 6.0). Where it supports forests it can be rich in humus. With soil conservation on the hills of Karnataka, Kerala and Tamil Nadu it grows tea and coffee, and red laterite in Tamil Nadu, Andhra Pradesh and Kerala suits cashew.

The name comes from the Latin later (brick), because the soil hardens and is cut into bricks for houses (NCERT).

Arid, saline, peaty and forest soils

• Arid soils (western Rajasthan). These are red to brown, sandy and saline. In places the salt content is high enough that common salt is obtained by evaporating the water. Calcium increases with depth and forms kankar layers in the lower horizons. NCERT notes that this layer restricts infiltration, so irrigation water stays available to plants. The soils are poor in humus and nitrogen, but phosphate is normal.
• Saline soils (usara). These contain more sodium, potassium and magnesium, which makes them infertile. NCERT gives three origins: a dry climate with poor drainage, seawater intrusion in deltas, and over-irrigation in the Green Revolution areas, where capillary action lifts salt to the surface. NCERT recommends gypsum for Punjab and Haryana. ICAR-CSSRI puts the salt-affected area at about 6.73 million ha, 2.1% of the geographical area, with sodic soils concentrated in the alluvial soils of the Indo-Gangetic plains (ICAR, citing ICAR-CSSRI Karnal; page accessed 1 Oct 2026). In soil science, saline soils (excess soluble salts) are distinguished from sodic (alkali) soils (excess exchangeable sodium, high pH). The ICAR-CSSRI reclamation example on that page reports sodic soils with pH 8.5-10.1, reclaimed with gypsum and pressmud.
• Peaty soils. These form where heavy rain, high humidity and dense vegetation leave large amounts of dead organic matter, up to 40-50%. They are heavy, black and in many places alkaline. NCERT's regions are north Bihar, southern Uttarakhand, and coastal West Bengal, Odisha and Tamil Nadu.
• Forest soils. These vary with the mountain environment: loamy and silty on valley sides, coarse on upper slopes, acidic and low in humus in the snow-bound Himalaya, and fertile on lower valley terraces and alluvial fans.

Soil degradation: what NCERT says and what the official figures add

NCERT defines soil degradation as "the decline in soil fertility, when the nutritional status declines and depth of the soil goes down due to erosion and misuse". Besides erosion, it names three causes:

• Over-irrigation brings salt up from lower soil layers to the surface.
• Chemical fertilisers used without organic manure harden the soil and lower its fertility in the long run. NCERT says this problem is common in the command areas of river-valley projects, which were the first beneficiaries of the Green Revolution.
• Over-grazing and shifting cultivation remove the natural vegetation cover.

NCERT gives the extent only as "about half of the total land of India". The two official national estimates in Table 5 are lower and use different methods. Class 10 adds a regional pattern for land degradation: mining in Jharkhand, Chhattisgarh, MP and Odisha; overgrazing in Gujarat, Rajasthan, MP and Maharashtra; and over-irrigation with waterlogging, salinity and alkalinity in Punjab, Haryana and western UP.

Soil conservation

NCERT's starting rule is that land with a slope gradient of 15-25% should not be cultivated. If it must be farmed, it should be terraced. The other measures are:

Source: NCERT Class 11 IPE, Ch. 6 (2021-22); NCERT Class 10 Contemporary India II, Ch. 1 (2026-27).

NCERT notes that the Central Soil Conservation Board prepared conservation plans for different regions, but calls them "fragmental". It recommends integrated land-use planning instead: classify land by its capability, map it, and put it to the right use.

PART 3 — UPSC Integration

Mains frames that need this chapter

• Soil, crop and region. Black soil and rain-fed cotton. Alluvium and the intensively cropped plains. Laterite, which becomes useful for plantations and cashew only with conservation and inputs.
• The irrigation paradox. NCERT's own example: the Green Revolution command areas that first gained from canal irrigation are the ones where over-irrigation, salinity and fertiliser use without manure now degrade the soil.
• Measurement. Two official degradation figures (Table 5) use different methods. A good answer names the source and year of each figure it uses.

Exam Strategy

Prelims fact-traps from this chapter:

• Largest USDA order is Inceptisols (39.74%), followed by Entisols (28.08%). Vertisols (the black-soil order) are 8.52% (NBSS&LUP Pub. 94, via NCERT).
• Alluvial share: NCERT says "about 40 per cent". Figures like 43% that appear in some guides are not from NCERT. The 40% is for the alluvial group; the 39.74% for Inceptisols is a USDA order, a different scheme, so do not equate them.
• Kankar is in both khadar and bhangar (Class 11) and more concentrated in bhangar (Class 10). A statement that "only bhangar contains kankar" is false.
• Laterite has iron oxide and potash in excess. It is poor in N, P, Ca and organic matter, and acidic (pH < 6.0).
• Black soil is rich in lime, iron, magnesia and alumina and contains potash. It is poor in phosphorus, nitrogen and organic matter.
• Saline-soil regions in NCERT are western Gujarat, the east-coast deltas, the Sundarbans and the Rann of Kachchh. Punjab and Haryana appear as irrigation-induced cases, with gypsum as the remedy.
• Peaty soils can be alkaline in many places (NCERT), so do not mark them as always acidic. Organic matter is up to 40-50%.
• Slope rule: land with a 15-25% gradient should not be cultivated, and should be terraced if it must be farmed.
• Soil Health Card: 12 parameters, of which 9 are nutrients. Launched at Suratgarh on 19 Feb 2015.

Mains pattern: Questions on soils usually come through other themes: the resources of a region (the Deccan Trap), desertification, regional disparity in agriculture, and watershed management. Write the soil facts into those frames instead of describing the soils in a list.

Practice Questions

Practice (UPSC-pattern, not past papers). Questions 1 to 4 are NCERT's own exercise MCQs.

Prelims:

1. Which one of the following is the most widespread and most productive category of soil?
   (a) Alluvial soil
   (b) Laterite soil
   (c) Black soil
   (d) Forest soil

2. "Regur soil" is another name for the:
   (a) Saline soil
   (b) Arid soil
   (c) Black soil
   (d) Laterite soil

3. Which one of the following is the main reason for the loss of the top soil in India?
   (a) Wind erosion
   (b) Water erosion
   (c) Excessive leaching
   (d) None of these

4. Arable land in the irrigated zones of India is turning saline due to which of the following reasons?
   (a) Addition of gypsum
   (b) Over grazing
   (c) Over irrigation
   (d) Use of fertilisers

5. With reference to Indian soils, consider the following statements: 1. Both khadar and bhangar contain calcareous concretions (kankar). 2. Inceptisols occupy the largest area among the USDA soil orders in India. 3. Laterite soils have excess iron oxide and potash but are poor in nitrogen and phosphate. Which of the statements given above are correct?
   (a) 1 and 2 only
   (b) 2 and 3 only
   (c) 1 and 3 only
   (d) 1, 2 and 3

Mains (practice):

1. What are black soils? Describe their formation and characteristics. (NCERT Ex. 3(i), 125 words)
2. What is soil conservation? Suggest some measures to conserve soil. (NCERT Ex. 3(ii), 125 words)
3. How do you know that a particular type of soil is fertile or not? Differentiate between naturally determined fertility and culturally induced fertility. (NCERT Ex. 3(iii), 125 words)
4. India's official land-degradation estimates range from about 98 to about 147 million hectares. Explain why they differ, and suggest how soil conservation should be targeted. (practice, 15 marks)

Short answers (NCERT Ex. 2, about 30 words): soil is the mixture of rock debris and organic material that develops on the earth's surface. Its formation depends on relief, parent material, climate, vegetation and other life forms, and time, and human activities also influence it to a large extent. A soil profile has three horizons: A, the topmost, where organic matter mixes with minerals, nutrients and water; B, a transition zone with matter from above and below; and C, loose parent material. Soil degradation is the decline in soil fertility, when the nutritional status declines and the depth of the soil goes down due to erosion and misuse. Khadar is new alluvium deposited by floods every year; bhangar is older alluvium away from the floodplain.

Worked answer, NCERT Ex. 3(iii) (built from the chapter's own text): whether a soil is fertile depends on its components (mineral particles, humus, water and air) and on its nutrients. A soil short of humus, nitrogen or phosphorus, a salt crust on the surface, or soil that has thinned through erosion are signs of low fertility; NCERT defines degradation as the decline in fertility when "the nutritional status declines and depth of the soil goes down". Naturally determined fertility is what the soil inherits from parent rock, climate and vegetation: alluvial soils are rich in potash, fine-grained red and yellow soils are normally fertile, while laterites lose lime, silica and humus to leaching and are poor in nitrogen, phosphate and calcium. Culturally induced fertility is what human use adds or takes away: manures and fertilisers make laterites fit for cultivation, and gypsum treats salinity in Punjab and Haryana; but over-irrigation raises salt to the surface, and chemical fertilisers without organic manure harden the soil and reduce its fertility in the long run.

📦 Revision Capsule

Sources

• NCERT, India: Physical Environment (Class 11), Chapter 6 "Soils", 2021-22 reprint (pre-rationalised). Archived copy, Wayback Machine, 18 Oct 2021. Includes the ICAR table sourced to NBSS&LUP Soils of India, Publication No. 94.
• NCERT, India: Physical Environment (Class 11), contents page, Reprint 2026-27 (kegy1ps.pdf): six chapters, Soils absent.
• NCERT, Contemporary India II (Class 10), Chapter 1 "Resources and Development", Reprint 2026-27. jess101.pdf
• Bhattacharyya, R. et al., "Soil Degradation in India: Challenges and Potential Solutions", Sustainability 7(4):3528-3570 (2015). MDPI
• PIB (MoEFCC), "Government releases Desertification and Land Degradation Atlas of India", 17 Jun 2021. PIB
• PIB (MoEFCC), "Land Degradation and Desertification", Lok Sabha written reply, 7 Aug 2023. PIB
• ICAR, "Farmers' participatory sodic soil reclamation…" (source: ICAR-CSSRI, Karnal), accessed 1 Oct 2026. ICAR
• ICAR and NAAS, Degraded and Wastelands of India: Status and Spatial Distribution, June 2010 (Table 1: NBSS&LUP 2004 revised, 146.82 Mha; grand total 120.72 Mha). ICAR PDF
• Dhruva Narayana, V. V. and Ram Babu, "Estimation of Soil Erosion in India", Journal of Irrigation and Drainage Engineering (ASCE) 109(4): 419-434, December 1983. DOI
• PIB (MoA&FW), "Implementation of the New Soil Health Card Scheme", Lok Sabha written reply, 4 Feb 2025. PIB
• Lok Sabha Unstarred Question No. 360, "Soil Health Card Scheme", answered 21 Jul 2026. Lok Sabha PDF
• PIB (MoA&FW), "Celebrating a Decade of Soil Health Cards", 19 Feb 2025. PIB backgrounder PDF