Classifying Indian soils

Detail

Why soils are grouped into classes

• Soil classification means sorting soils into groups that share the same features. This lets farmers, planners and map-makers treat similar soils in the same way.
• The bases used to classify soils:
• Factors of formation: the parent rock, climate, relief, vegetation and time that made the soil.
• Colour, for example black regur and red soils.
• Thickness, meaning how deep the soil is.
• Texture, meaning the share of sand, silt and clay in it.
• Age, for example old alluvium against new alluvium.

• Chemical and physical properties, such as pH, salts, organic matter and how much water the soil holds.

• Why India has so many soils:

• India has very different relief and landforms: the Himalaya, the Indo-Gangetic plains, the Peninsular plateau, the Thar desert and long coasts.
• Its climates range from more than 1,000 cm of rain in the North-East to under 25 cm in western Rajasthan.
• Its vegetation also varies a lot.
• Different mixes of rock, climate and vegetation give different soils.

The traditional and textbook groupings

• Amarakosha: an ancient Sanskrit word-book (lexicon) by Amarasimha. It names twelve kinds of farmland, sorted by how fertile they are. Examples:
• urvara: fertile land
• ushara: barren land
• maru: desert
• aprahata: fallow land
• shadvala: grassy land
• pankikala: muddy land
• nadimatruka: land watered by a river
• devamatruka: land that depends on rain

• This shows that Indians classified soils long before modern science.

• Six major types in the school-level grouping: 1. Alluvial 2. Black 3. Red 4. Laterite 5. Desert 6. Mountain or alpine

The ICAR eight-group classification

• ICAR (Indian Council of Agricultural Research) is India's top body for farm research.
• The All India Soil Survey Committee was set up in 1953. After its work, ICAR recognised eight major soil groups.
• Four of the eight groups matter most for farming: alluvial, black, red and lateritic soils [4].

#	ICAR group	Main parent material / process	Main areas in India	Rough USDA order
1	Alluvial	Silt laid down by rivers	Indo-Gangetic plain (Punjab to West Bengal), Brahmaputra valley (Assam), east-coast deltas (Mahanadi, Godavari, Krishna, Kaveri)	Entisols, Inceptisols
2	Black (regur)	Weathered basalt lava of the Deccan Traps	Maharashtra, Gujarat, Madhya Pradesh (Malwa), Karnataka, Telangana	Vertisols
3	Red and yellow	Old crystalline and metamorphic rocks (granite, gneiss)	Tamil Nadu, Karnataka, Andhra Pradesh, Odisha, Chhattisgarh, Jharkhand	Alfisols
4	Laterite	Heavy rain and high heat wash away silica, leaving iron and aluminium oxides	Kerala, Karnataka, Goa, Western Ghats, hills of Odisha and the North-East	Ultisols (some Alfisols)
5	Arid (desert)	Sand moved by wind; very little organic matter	Western Rajasthan (Thar), Kachchh in Gujarat	Aridisols
6	Saline and alkaline	Salts rise to the surface through evaporation, poor drainage or too much canal irrigation	Kachchh Rann, Punjab, Haryana and western Uttar Pradesh (canal areas), coastal deltas	Aridisols / Inceptisols (salty phases)
7	Peaty and marshy	Plant matter piles up in waterlogged, wet areas	Kerala (Kuttanad, Alappuzha), Sundarbans delta (West Bengal), coastal Odisha, north Bihar	Histosols
8	Forest and mountain	Thin, young soils on slopes under forest	Himalaya (J&K to Arunachal Pradesh), Western and Eastern Ghats	Inceptisols, Entisols, some Mollisols

• Area facts (FAO, 2005):
• Alluvial soils cover about 75 million ha in the Indo-Gangetic plains and the Brahmaputra valley alone [4].
• Black soils cover about 74 million ha, mainly in central, western and southern states [4].

• Laterite and lateritic soils cover about 25 million ha, in Kerala, Tamil Nadu, Karnataka, Andhra Pradesh and the North-East [4].

• Area ranking by share of India's land:

• Alluvial soils are the largest group, about two-fifths of India. The 75 million ha figure above leaves out the deltas and coastal plains, so the full alluvial area is larger.
• Red soils come second.
• Black soils come third.
• The order is alluvial > red > black > laterite or arid.

The scientific system: NBSS&LUP and USDA Soil Taxonomy

• NBSS&LUP: the National Bureau of Soil Survey and Land Use Planning, in Nagpur, Maharashtra. It is the ICAR institute that surveys and maps India's soils.
• USDA Soil Taxonomy: a world system made by the United States Department of Agriculture. It groups soils by layers and properties that can be measured, and not by colour alone. Its biggest groups are called orders. Order names end in "-sols".
• Orders found in India, explained simply:
• Entisols: very young soils with almost no layers. Examples are fresh river silt (khadar) and sand dunes. → new alluvium.
• Inceptisols: young soils with just-starting layers. Example: older alluvium (bhangar). → alluvium.
• Vertisols: clay soils that swell when wet and crack deeply when dry. → black soils.
• Alfisols: moderately weathered soils with clay in the lower layers and fairly good fertility. → red soils.
• Ultisols: deeply weathered, acidic and leached soils of hot, wet areas. → laterite-type soils.
• Aridisols: dry-region soils, often with lime or salt layers. → desert soils.

• Mollisols: dark soils rich in humus. They are found in small patches in the Himalayan foothills and the Terai.

• How NBSS&LUP mapped India:

• It used satellite imagery to make a soil map of the whole country at 1:250,000 scale.
• It published the map at 1:500,000 [2].
• Mapping at 1:50,000 scale covered 119.37 million ha (DOS, 1999) [2].

• Up to 1983, detailed soil surveys covered 33.5 million ha and reconnaissance (quick, broad) surveys covered 115.0 million ha (Task Force, 1984) [2].

• Limits of mapping soils from satellites:

• Vertisols and Mollisols are both dark, so they reflect light in a similar way and are hard to tell apart in images [2].
• Vertisols and deltaic alluvium can be confused in the same way [2].
• So can red and lateritic soils [2].
• Because of this, field checks are needed.

From national maps to farm-level testing: Soil Health Card (2015)

• The soil classes above describe regions. A Soil Health Card (SHC) describes the soil of one farm.
• Launch: the Soil Health Card Scheme began on 19 February 2015 at Suratgarh, Rajasthan [3]. This was during the UN International Year of Soils (2015).
• 12 parameters tested [3]:
• Macro-nutrients: Nitrogen (N), Phosphorus (P), Potassium (K) and Sulphur (S).
• Micro-nutrients: Zinc (Zn), Iron (Fe), Copper (Cu), Manganese (Mn) and Boron (B).

• Physical and chemical parameters: pH (how acidic or basic the soil is), EC (electrical conductivity, which measures salt content) and OC (organic carbon).

• What the card gives: a fertiliser dose for the farm and any soil amendment it needs, such as gypsum for alkaline soil or lime for acidic soil [3].

• When samples are taken: usually twice a year, after the rabi and kharif harvests [3].
• Merger: since 2022-23 the scheme is part of RKVY (Rashtriya Krishi Vikas Yojana) as the component "Soil Health & Fertility" [3].
• Geospatial link:
• In April 2023 the SHC portal was rebuilt with GIS (Geographic Information System: software that shows data on maps) [3].
• The mobile app records each sample's latitude and longitude automatically [3].
• It links each sample to its result through a QR code [3].

• Results can be viewed by state, district, taluka, panchayat and cadastral (land-parcel) boundaries [3].

• Village Level Soil Testing Labs (VLSTLs):

• Guidelines came out in June 2023. Rural youth aged 18–27, SHGs and FPOs can set up these labs [3].

• By February 2025, there were 665 VLSTLs in 17 states [3].

• School Soil Health Programme: by 2024, 1,020 schools had joined, with 1,000 labs and 125,972 students enrolled [3].

Map practice

• On one outline map of India, shade all eight ICAR groups:
• Alluvial: the plain of the Sutlej, Ganga and Brahmaputra, plus the east-coast deltas.
• Black: the Deccan Trap triangle and the Malwa plateau.
• Red: Tamil Nadu, the Chhotanagpur plateau and Odisha.
• Laterite: the Western Ghats, Kerala and the Meghalaya plateau.
• Arid: west of the Aravallis.
• Saline: the Rann of Kachchh, plus patches in Punjab and Haryana.
• Peaty: Kuttanad and the Sundarbans.

• Mountain: the Himalayan arc.

• Practise with the "India: Major Soil Types" map (Class 10) and Fig. 1.9 (Class 7).

Prelims Hooks

• ICAR's eight soil groups came after the All India Soil Survey Committee (1953). The six-type list is the school-level grouping. Don't mix them up.
• Of the 8 groups, the four farming soils are alluvial, black, red and lateritic [4].
• Area order: alluvial (about two-fifths of India) > red > black.
• USDA order matches: Vertisols = black (regur). Alfisols = red. Entisols and Inceptisols = alluvium. Aridisols = desert. Ultisols = laterite-type.
• NBSS&LUP is in Nagpur. It mapped all of India at 1:250,000 using satellite imagery and published at 1:500,000 [2].
• Amarakosha lists 12 kinds of farmland, sorted by fertility.
• Soil Health Card: launched 19 February 2015 at Suratgarh (Rajasthan). It tests 12 parameters. It became part of RKVY in 2022-23 [3].
• Trap: Sulphur is a macro-nutrient on the card, and Boron is a micro-nutrient [3].
• Peaty and marshy soils match Kuttanad (Kerala) and the Sundarbans (West Bengal). Saline soils match the Rann of Kachchh.

Mains Points

• Why India has so many soils (GS-I):
• Relief varies: the Himalaya, the plains, the plateau and the desert.
• Rainfall varies, from more than 1,000 cm in the North-East to under 25 cm in the Thar.
• Parent rock varies: Deccan basalt gives black soil, Archaean granite gives red soil, and river silt gives alluvium.

• These variations give eight soil groups, each linked to different crops (alluvium–wheat and rice, regur–cotton, laterite–plantations).

• Colour-based classes against the USDA system:

• Classes based on colour and formation are easy to teach but blur differences inside each class.

• USDA Soil Taxonomy, used by NBSS&LUP, is based on measured properties. It allows comparison with other countries and land-use planning at 1:250,000 to 1:50,000 scale [2].

• Geospatial use and its limits:

• Satellite maps cover the whole country quickly.

• But dark soils (Vertisols and Mollisols) and red and lateritic soils look alike in the images, so field checks are still needed [2].

• From national maps to farm-level advice (GS-III):

• The Soil Health Card, with geotagged sampling and GIS since 2023, turns broad soil maps into a fertiliser plan for each farm.
• This helps correct the overuse of N-P-K fertilisers.
• Village labs and school labs (2023–25) bring soil testing closer to farmers [3].