Alluvial soil is a depositional (azonal) soil formed by the silt, sand, and clay carried and laid down by rivers, floods, and marine action rather than by in situ weathering of underlying rock. In India it is the most widespread soil group, covering roughly 40 per cent of the land area — about 15 lakh square kilometres — across the Indo-Gangetic-Brahmaputra plains, the Narmada-Tapi valleys, and the coastal and deltaic tracts of the Mahanadi, Godavari, Krishna, and Kāverī. The Indian Council of Agricultural Research (ICAR) and the National Bureau of Soil Survey and Land Use Planning (NBSS&LUP) classify it within the orders Entisols and Inceptisols, reflecting its youthful, weakly developed soil profile. It is rich in potash and lime but generally deficient in nitrogen, phosphorus, and humus.
The defining classification of Indian alluvium is the distinction between Khadar and Bhangar. Khadar is the newer alluvium of the active floodplains, renewed annually by fresh silt during inundation, light in colour, finer in texture, and highly fertile. Bhangar is the older alluvium of the terraces above the flood limit, darker, more clayey, often containing concretionary nodules of impure calcium carbonate known as kankar. Coastal alluvium and deltaic alluvium form a further subtype, frequently marred by salinity and the presence of reh or kallar (saline-alkaline efflorescence). Because alluvial soils are constantly replenished and naturally porous, they need little fallowing and respond strongly to irrigation, making them the backbone of intensive cereal cultivation.
These soils sustain India's principal foodgrain belt: wheat and rice in the Punjab-Haryana-Uttar Pradesh tract, sugarcane and oilseeds, and jute in the Ganga-Brahmaputra delta of West Bengal. The Green Revolution of the late 1960s succeeded precisely because the alluvial plains combined level terrain, deep soils, and assured canal and tubewell irrigation. As of 2026, however, large stretches of Punjab and western Uttar Pradesh face declining fertility, waterlogging, salinisation, and falling water tables, prompting policy emphasis on the Soil Health Card scheme (2015), balanced nutrient use, and crop diversification away from the paddy-wheat monoculture. Riverine alluvium of the Brahmaputra valley remains vulnerable to recurrent flooding and bank erosion.
For the UPSC examination, alluvial soil is a high-frequency topic in the General Studies Paper I physical and economic geography syllabus and in the Geography optional. Prelims questions typically test the Khadar-versus-Bhangar distinction, the chemical composition (potash- and lime-rich, nitrogen-poor), and the kankar/reh terminology; mapping questions link soil type to the cropping pattern of a region. Mains answers should connect alluvial fertility to the geography of the Green Revolution, food security, and contemporary soil-degradation challenges, integrating ICAR/NBSS&LUP classification with the river systems that create the deposits.
Example
In 1968, the early Green Revolution concentrated high-yielding wheat in the Khadar alluvium of Punjab and Haryana, where annual silt renewal and tubewell irrigation tripled per-hectare cereal output within a decade.
Frequently asked questions
Khadar is the newer, finer, lighter alluvium of active floodplains, renewed by fresh silt each year and highly fertile. Bhangar is the older, darker, more clayey terrace alluvium lying above the flood limit and often containing kankar (calcium carbonate nodules).