The accumulation of water-soluble salts in the soil, to levels harmful to crops, is known as:

Salinisation (also spelt salinization) is the process by which water-soluble salts, such as those of sodium, calcium and magnesium (chlorides, sulphates and carbonates), build up in the soil, especially near the surface. When salt levels become high, the soil becomes unfit for most crops.

Causes of salinisation:

Natural causes:

• In arid and semi-arid regions, groundwater rises to the surface through capillary action, and when the water evaporates, the dissolved salts are left behind.
• Salts may be present in the parent rock or deposited by wind and sea spray in coastal areas.

Human-induced (secondary) causes:

• Over-irrigation and poor drainage cause the water table to rise (waterlogging), bringing salts to the surface.
• Use of saline groundwater for irrigation.
• Seepage from unlined canals.

Effects:

• High salt concentration makes it difficult for plant roots to absorb water (physiological drought).
• Some salts, especially sodium, are toxic to plants and damage soil structure, making it hard and impermeable.
• Crop yields fall, and in severe cases the land becomes barren, often showing a white crust of salt on the surface.

Where it occurs in India:

• In the canal-irrigated areas of Punjab, Haryana, Uttar Pradesh and Rajasthan, especially in the command areas of large irrigation projects.
• In coastal areas of Gujarat, the Sundarbans and the deltas of the east coast.
• In the Rann of Kutch, where salt deposits are naturally high.

Reclamation of saline and alkaline soils:

• Providing proper drainage to wash out excess salts (leaching with good-quality water).
• Adding gypsum (calcium sulphate) to alkaline (sodic) soils, which replaces sodium with calcium.
• Growing salt-tolerant crops such as barley, cotton, sugar beet and some rice varieties.
• Adding organic matter and green manure.
• The Central Soil Salinity Research Institute (CSSRI), Karnal (Haryana), works on reclaiming such soils.

Why not the other options?

• ✗Leaching is the removal of soluble minerals from the upper soil by percolating rainwater, which is the opposite process.
• ✗Podzolisation is a process in cool, humid coniferous forests, which forms acidic, ash-grey soils (podzols).
• ✗Laterisation forms laterite soils in hot, wet-dry tropical climates.