BharatNotes What is Soil Salinity and Alkalinity?
Salt-affected soils are degraded soils in which excess salts or sodium impair crop growth. Two distinct problems are grouped here:
- Salinity — too many soluble salts in the root zone, measured by the electrical conductivity of the saturation extract (ECe). Saline soils typically have ECe of 4 dS/m or more, ESP below 15, and pH usually below 8.5, often showing a white salt crust.
- Alkalinity / sodicity — too much exchangeable sodium on the clay complex, measured by the Exchangeable Sodium Percentage (ESP). Sodic (alkali) soils have ESP of 15 or more, ECe below 4 dS/m, and high pH (generally 8.5–10, sometimes above 11). They are often called "wet deserts" because the dispersed clay seals the surface.
Where both occur together, the soil is termed saline-sodic (ECe ≥ 4 dS/m and ESP ≥ 15).
Classification at a Glance
| Type | ECe (dS/m) | ESP | pH | Key behaviour |
|---|---|---|---|---|
| Saline | ≥ 4 | < 15 | usually < 8.5 | Salts flocculate clay; white crust |
| Sodic (alkali) | < 4 | ≥ 15 | 8.5–10+ | Clay disperses; poor drainage |
| Saline-sodic | ≥ 4 | ≥ 15 | variable | Combined stress |
Thresholds follow the U.S. Salinity Laboratory / USDA standard, widely used in India.
Extent and Significance in India
According to ICAR-CSSRI, about 6.73 million hectares of India's land is salt-affected, split roughly between saline soils (around 44%, across coastal and arid states) and sodic soils (around 47%, concentrated in the Indo-Gangetic plains of Uttar Pradesh, Punjab, Haryana and parts of Rajasthan and Gujarat). CSSRI's Vision 2050 projects this could rise to about 16.2 million hectares by 2050 if irrigation and drainage practices remain unchanged, threatening food security on otherwise fertile land.
Reclamation and Management
The principal remedy differs by soil type:
- Sodic/alkali soils — chemical amendment with gypsum (calcium sulphate), which replaces sodium with calcium, followed by leaching. CSSRI recommends roughly 10–15 tonnes of gypsum per hectare after levelling, bunding and ponding water. Through this gypsum technology, India has reclaimed roughly 2 million hectares of sodic land (CSSRI estimate), adding substantial grain to the national pool.
- Saline soils — managed mainly by improved drainage, leaching of salts, and salt-tolerant crop varieties rather than gypsum.
Complementary measures include sub-surface drainage in waterlogged saline tracts, salt-tolerant rice and wheat varieties, agroforestry on salty land, and organic amendments (pressmud, green manure, fly ash) to cut gypsum use.
UPSC Angle
Expect Prelims questions to hinge on the precise EC/ESP/pH distinction and on the fact that gypsum reclaims sodic, not saline, soils. For Mains GS3, link salinity to land degradation, waterlogging from canal irrigation, soil health, and sustainable/climate-resilient agriculture, citing CSSRI as the nodal institute. A common trap is treating "saline" and "alkaline/sodic" as synonyms — they are diagnostically different problems requiring different solutions.
