BharatNotes What is Black Soil (Regur)?
Black soil — known in India as regur or black cotton soil — is a dark, clayey, highly moisture-retentive soil derived from the weathering of the basaltic lava of the Deccan Traps. The Deccan Trap flood basalts erupted roughly 66 million years ago, across the Cretaceous–Paleogene (K–Pg) boundary (Deccan Traps, geological dating). As this basalt weathered under semi-arid conditions, it produced a deep, fine-grained, clay-rich soil. In modern soil taxonomy (USDA / NBSS&LUP), regur is classified as a Vertisol — a soil order defined by its very high clay content and shrink–swell behaviour.
Key Features
- Texture: highly argillaceous (clayey); clay content can exceed 60%, making the soil heavy and fine-grained.
- Shrink–swell behaviour: swells and becomes sticky when wet; shrinks and develops wide, deep cracks when dry. These cracks let the topsoil tumble in, giving regur its "self-ploughing" (self-mulching) property and high water-retention capacity.
- Colour: deep black to chestnut-brown, attributed to iron, titaniferous magnetite and humus content.
- Chemistry: rich in lime, iron, magnesia, alumina and potash; deficient in nitrogen, phosphorus and organic matter (humus).
- Workability: difficult to plough when wet (sticky) and very hard when dry, so it is best tilled immediately after the first rains.
Distribution in India
Regur covers a major share of India's geographical area and is concentrated on the Deccan and Malwa plateaus.
| Aspect | Detail (as per soil-survey data) |
|---|---|
| Share of India's area | About 15–16% of total geographical area |
| Leading state | Maharashtra (largest share of black-soil area) |
| Other key states | Madhya Pradesh, Gujarat, Karnataka, Andhra Pradesh, Telangana, Tamil Nadu |
| Parent material | Deccan Trap basalt (and Malwa lavas) |
| Taxonomic class | Vertisol |
Agricultural Significance
Regur's outstanding moisture-retention makes it ideal for rain-fed cotton, the crop that gives it its popular name. Other important crops include wheat, jowar (sorghum), millets, linseed, castor, tobacco, sunflower, pulses and oilseeds; where irrigation is available, sugarcane and rice are also grown. The soil supports India's major cotton and sugarcane belts, especially in Maharashtra and Gujarat. Because regur is naturally low in nitrogen, phosphorus and humus, farmers supplement it with fertilisers and organic manure for sustained yields.
UPSC Angle
For Prelims (GS1), focus on the parent rock (basalt), the Vertisol classification, the self-ploughing/shrink–swell property, the nutrient profile (rich in lime/iron/magnesia, poor in N/P/humus), and the cotton link. For Mains (GS1/GS3), regur is relevant to agriculture, cropping patterns and rain-fed farming in the Deccan. A common exam trap is confusing the chemical richness (lime, iron) with nutrient poverty (nitrogen, phosphorus) — regur is both. This is a foundation concept that underpins the wider question family on Indian soils, agro-climatic regions and the Deccan Plateau.
