Alluvial soils: khadar and bhangar

Detail

What alluvial soil is

• Alluvial soil is soil built up from alluvium, the sand, silt and clay that rivers carry and drop.
• A river slows down on flat land, so it loses the energy to carry its load.
• The load settles layer by layer on the plain and in the delta.

• Over thousands of years these layers become deep, soft soil.

• It is the most widespread and most important soil of India.

• In the ICAR scheme it is the first of 8 soil groups: alluvial, black, red and yellow, laterite, arid, saline, peaty and forest. (ICAR is the Indian Council of Agricultural Research.)

Where it is found: spatial anchors

Belt	Rivers that laid it down	Where
Northern Plains (the whole belt)	Indus, Ganga, Brahmaputra and their tributaries	Punjab, Haryana, Uttar Pradesh, Bihar, West Bengal, Assam
Narrow corridor to the west	Extends from the Indus–Ganga plain	North Rajasthan into the plains of Gujarat
East-coast deltas	Mahanadi, Godavari, Krishna, Kaveri	Odisha, Andhra Pradesh, Tamil Nadu; all drain into the Bay of Bengal

• The three Himalayan rivers that built the Northern Plains:
• Indus: rises in Tibet near Lake Mansarovar and flows to the Arabian Sea. Its plain in India is the Punjab–Haryana tract.
• Ganga: rises at the Gangotri glacier in Uttarakhand and flows into the Bay of Bengal. It builds the largest part of the plain, with tributaries such as the Yamuna, Ghaghara, Gandak and Kosi.

• Brahmaputra: rises in Tibet as the Tsangpo, enters India in Arunachal Pradesh and builds the Assam valley. It joins the Ganga to form the Ganga–Brahmaputra delta, the world's largest delta.

• The four Peninsular deltas, from north to south:

• Mahanadi: rises in Chhattisgarh; delta in Odisha.
• Godavari: rises at Trimbakeshwar, Nashik (Maharashtra); delta in Andhra Pradesh.
• Krishna: rises near Mahabaleshwar (Maharashtra); delta in Andhra Pradesh.

• Kaveri: rises at Talakaveri, Kodagu (Karnataka); delta in Tamil Nadu (Thanjavur area).

• Deltaic soils (soils of river deltas) are alluvial soils, and NCERT asks about them in its exercises.

How grain size changes from the hills to the plains

• Cause → process → result:
• A river comes out of the Himalaya at the break of slope: the point where steep hills suddenly meet flat land.
• The river slows sharply. It drops its heaviest load first: boulders, pebbles and coarse sand.

• Lighter silt and clay travel further and settle far inland and in the deltas.

• So the soil is coarse in the piedmont plains (plains at the foot of mountains) and finer further inland.

• Piedmont belts named in NCERT:
• Duars: the foothill plains of north Bengal and Assam.
• Chos: the seasonal streams and their gravelly fans at the foot of the Shiwaliks in Punjab.
• Terai: the marshy foothill belt of Uttar Pradesh, Bihar and Uttarakhand.

Northern fringe: bhabar and terai (Beyond NCERT link to india-structure-physiography)

• Bhabar: a narrow belt of pebbles and boulders, about 8–16 km wide, at the foot of the Shiwaliks. The soil is so porous that streams sink underground and disappear.
• Terai: a wet, marshy, once-forested belt just south of the bhabar. Here the hidden streams come back to the surface.
• Order from the mountains to the river: Shiwalik → bhabar → terai → bhangar → khadar.

Age-based division: bhangar and khadar

Feature	Bhangar (old alluvium)	Khadar (new alluvium)
Position	Higher, terraced land above flood level	Low floodplains next to the river
Renewal	Not flooded, so no fresh silt	Renewed by floods every year
Texture	Coarser; has kankar nodules	Finer particles
Fertility	Less fertile	More fertile

• Bhangar is the slightly raised, terraced land made of older alluvium [3][4].
• Khadar is the more fertile, fresh alluvium on the low floodplain [3][4].
• Moving upstream, bhangar covers more land compared with khadar. This is true along all the major rivers [3][4].
• Upstream: the river cuts deep into old terraces, so most of the land is bhangar.
• Downstream: the floodplains are wider, so khadar covers more ground.

Kankar

• Kankar: small lumps (nodules) of calcium carbonate (lime) in the soil.
• How it forms:
• In moderate rainfall, water soaks down and dissolves lime from the upper soil.
• The water does not drain fully away. It dries out at some depth.

• The lime comes out of the water and builds up into hard nodules.

• It is typical of bhangar. It is also found in the lower layers of arid soils, where it blocks water from soaking down (see the Section 6 note on arid soils).

Properties

• Rich in: potash, phosphoric acid and lime.
• Poor in: nitrogen and humus (humus is rotted plant and animal matter), so farms need fertiliser (Beyond NCERT).
• Example: a rice–wheat farm in Nalanda district, Bihar, in the middle Ganga plain, had its soil tested under the Soil Health Card scheme. The soil lacked organic carbon, nitrogen, phosphate and boron and had high electrical conductivity (a sign of salt build-up) [2].

• Adding compost and cow-dung manure along with the advised DAP and urea doses raised the yield to 32 quintals/ha, against 27.5 quintals/ha on the farmer's usual field. That is over 16% more (PIB, August 2025) [2].

• Drier areas: alluvium there is more alkaline, so it needs treatment and irrigation before it gives good crops.

• Low rain does not wash salts out of the soil.
• Water rises through the soil and evaporates, leaving salts on top.
• The result is white salt crusts called reh or kallar in parts of Uttar Pradesh, Haryana and Punjab. Gypsum and good drainage are used to treat them.

Crops and population

• Crops: sugarcane, paddy (rice), wheat, other cereals and pulses.
• Fertile soil, flat land and easy canal and well irrigation make these areas intensively cultivated (farmed heavily, often with 2–3 crops a year).
• So they are among the most densely populated parts of India. The Ganga basin is the classic example.

Soil Health Card scheme: testing alluvial farms

• Launched: 19 February 2015 by the Prime Minister at Suratgarh, Rajasthan. 2015 was the International Year of Soils [2].
• Since 2022–23 it has been a part of the Rashtriya Krishi Vikas Yojana, under the name "Soil Health and Fertility" [2].
• 12 parameters tested [2]:
• macro-nutrients: N, P, K, S
• micro-nutrients: Zn, Fe, Cu, Mn, B

• pH, EC (electrical conductivity) and OC (organic carbon)

• Sampling: samples come from 15–20 cm depth, on a grid of 2.5 ha in irrigated areas and 10 ha in rain-fed areas [2]. Most alluvial plains are irrigated, so they get the finer 2.5 ha grid.

• Progress:
• Over 25 crore cards given out (July 2025) [2].
• 8,272 soil-testing labs (February 2025) [2].
• Soil mapping at 1:10,000 scale over about 290 lakh ha, including 40 aspirational districts [2].
• 1,987 village-level fertility maps for 21 States and UTs (February 2025) [2].

Prelims Hooks

• Alluvial soil is the most widespread soil group of India and the first of ICAR's 8 groups.
• Khadar = new, floodplain, renewed every year, finer, more fertile. Bhangar = old, terraces above flood level, kankar, less fertile. A common trap is a question that swaps the two.
• Kankar = calcium carbonate nodules. They mark bhangar and the lower layers of arid soils.
• Moving upstream, the share of bhangar compared with khadar increases [3][4].
• Order from the hills southward: Shiwalik → bhabar (streams sink) → terai (streams re-emerge, marshy) → bhangar → khadar.
• Grain size: coarse at the break of slope (duars, chos, terai) and fine inland and in deltas.
• Alluvial soil is rich in potash, phosphoric acid and lime and poor in nitrogen and humus.
• East-coast alluvial deltas from north to south: Mahanadi → Godavari → Krishna → Kaveri. All drain into the Bay of Bengal.
• Soil Health Card scheme: launched 19 February 2015 at Suratgarh (Rajasthan). It tests 12 parameters and was merged into RKVY from 2022–23 [2].
• Reh / kallar = salt crusts on alkaline alluvium in drier parts of UP, Haryana and Punjab.

Mains Points

• Distribution pattern (GS-I): the Himalayan rivers keep bringing fresh silt, so the Indus–Ganga–Brahmaputra plain has deep, well-sorted alluvium. Grain size goes from coarse (bhabar and terai) to fine (khadar and deltas). This pattern explains why farming and population are most intense in the middle and lower Ganga plain and the east-coast deltas.
• Hidden fertility problem (GS-III): alluvium is rich in potash and lime but poor in nitrogen and humus. Rice–wheat systems that run on heavy chemical fertiliser are wearing down organic carbon and micronutrients, as the Nalanda soil test shows [2]. Soil-test-based balanced and integrated nutrient management through Soil Health Cards (over 25 crore issued by July 2025) is the policy response [2].
• Problems of drier alluvium: salt and alkali build-up (reh/kallar) in the irrigated plains of Punjab, Haryana and western UP lowers yields. The fixes are gypsum, better drainage and careful canal irrigation.
• Floods and fertility: the same yearly floods that renew khadar also wreck lives and property, for example on the Kosi and in Assam. Embankments that stop floods also stop the fresh silt, so flood control must be weighed against soil renewal.