1. Saline Soils
Saline soils are those in which the electrical conductivity (EC) of the saturation extract is > 4 dS/m and the Exchangeable Sodium Percentage (ESP) is < 15. Their pH is usually below 8.5. They were once called “white alkali” soils because a white crust of salts often appears on the surface.
How saline soils form (Salinization)
Salinization describes the gradual buildup of salts in the soil profile. It happens mainly in dry climates where:
- Rainfall is too low to flush salts out of the root zone (insufficient leaching), and
- High evaporation draws water upward through the soil, leaving salts behind at or near the surface.
Major problems for crops
- Reduced water uptake: High salt lowers the osmotic potential of soil water, so roots must work harder to take up water.
- Poor nutrient uptake: Salt stress often reduces the plant's ability to absorb nutrients, slowing growth.
- Lower microbial activity: Many beneficial soil microbes decline in salty soils, harming decomposition and nutrient cycling.
- Ion toxicity: Specific ions (e.g., chloride, sulfate) can be toxic to sensitive crops.
2. Management & Reclamation
Reclaiming saline soils usually aims to remove or relocate salts from the root zone and to improve soil structure and fertility. Successful reclamation combines drainage, irrigation management, organic amendments, and careful cultural practices.
2.1 Reclamation measures
- Leaching with good-quality water: Apply sufficient irrigation water to flush salts below the root zone (provided drainage is available).
- Open drainage channels: Construct lateral and main drains (typical guideline: ~60 cm deep × ~45 cm wide) to carry away leachate and lower the water table.
- Sub-surface drainage: Tile drains or buried pipes can be effective where surface drainage is not feasible; they reduce shallow water tables and prevent secondary salinization.
2.2 Irrigation management
- Blend waters: If only saline water is available, mixing it proportionally with better-quality water reduces the salinity load.
- Alternate furrow irrigation: Watering alternate furrows lowers salt buildup around plant roots compared with continuous flooding.
- Micro-irrigation: Drip, sprinkler, and pitcher systems use water efficiently and keep salts from concentrating at the soil surface as much as flood irrigation does.
2.3 Fertilizer and organic amendments
- Extra nitrogen: Adding about 20–25% more N than standard recommendations can help compensate for low N availability in saline soils.
- Organic matter: Farmyard manure, compost, and other organic inputs improve soil structure, increase microbial activity, and release organic acids during decomposition that help mitigate salt effects.
- Green manures: Crops such as sunhemp, daincha, and kolingi add biomass and nutrients and help improve soil physical and chemical conditions.
2.4 Soil and cultural practices
- Bed design: Avoid sowing seeds at the center of raised beds where salts commonly accumulate; instead, slope beds and place seeds just above the waterline.
- Alternate furrow irrigation: Useful to displace salts away from seed rows and rooting zones.
- Mulching: Straw or similar mulches reduce evaporation from the soil surface and can lower salt concentration in the root zone within a few weeks.
Crop Choice / Crop Management
Crops are to be chosen based on the soil salinity level. The relative salt tolerance of different crops is as follows:
Relative tolerance of crops to salinity
| Plant species | Threshold salinity (dS m-1) | Plant species | Threshold salinity (dS m-1) |
|---|---|---|---|
| Field crops | Vegetables | ||
| Cotton | 7.7 | Tomato | 2.5 |
| Sugarbeet | 7.0 | Cabbage | 1.8 |
| Sorghum | 6.8 | Potato | 1.7 |
| Wheat | 6.0 | Onion | 1.2 |
| Soybean | 5.0 | Carrot | 1.0 |
| Groundnut | 3.2 | Fruits | |
| Rice | 3.0 | Citrus | 1.7 |
| Maize | 1.7 | - | - |
| Sugarcane | 1.7 | - | - |
3. Summary
Saline soils are a major constraint in dry regions but are manageable. Understanding salinization, applying proper drainage and irrigation techniques, and improving soil health with nutrients and organic matter can restore productivity and help farmers maintain yields in affected areas.
References / Further reading
- ICAR & State Agricultural University publications on salt-affected soils
- Central Soil Salinity Research Institute (CSSRI) resources
- Textbooks on soil science and land reclamation
