Introduction
India possesses approximately 6.73 million hectares (Mha) of salt-affected soils, which significantly curtail agricultural productivity. Sustainable reclamation requires a precise diagnostic classification based on USDA criteria—Electrical Conductivity (EC), Exchangeable Sodium Percentage (ESP), Sodium Adsorption Ratio (SAR), and soil pH—to differentiate between saline (white alkali) and sodic (black alkali) soil environments.
Characteristics of Saline Soil Reclamation (White Alkali)
Saline soils are chemically defined by an EC > 4 dS/m, ESP < 15%, SAR < 13, and pH < 8.5. The primary reclamation mechanism relies on the physical removal of excess neutral soluble salts (primarily chlorides and sulfates of sodium, calcium, and magnesium).
- Hydro-Physical Leaching: Flooding or continuous ponding with good quality water dissolves and flushes excess salts below the root zone. The volume of water needed is determined using the Leaching Requirement (LR = ECiw / ECdw).
- Subsurface Drainage (SSD) Systems: Installation of perforated corrugated PVC pipes embedded in gravel filters lowers shallow, saline water tables, preventing secondary salinization as demonstrated by ICAR-CSSRI interventions in Haryana and Gujarat.
- Agronomic Interventions: Surface mulching is employed to arrest capillary rise and subsequent salt deposition on the surface layer. Initial cropping cycles prioritize high salt-tolerant species such as barley, sugarbeet, mustard, and halophytic species like Salvadora persica.
Characteristics of Sodic Soil Reclamation (Black Alkali)
Sodic soils are characterized by an EC < 4 dS/m, ESP > 15%, SAR > 13, and pH > 8.5. High exchangeable sodium causes deflocculation and clay dispersion, resulting in poor aeration, low hydraulic conductivity, and crusting. Reclamation requires chemical replacement of exchangeable sodium prior to salt leaching.
- Chemical Amendments: Application of calcium-supplying agents like Gypsum (CaSO4·2H2O) or acid-formers like Iron Pyrites (FeS2) replaces exchangeable sodium with calcium on the soil exchange complex:
2Na+[Soil] + CaSO4·2H2O → Ca2+[Soil] + Na2SO4↓
The displaced soluble sodium sulfate (Na2SO4) is then safely leached out. - Physical and Mechanical Practices: Deep subsoiling and chiseling break through sodium-induced impermeable hardpans (such as calcic or natric horizons), improving water infiltration and root penetration.
- Biological and Organic Management: In-situ green manuring with Sesbania aculeata (Dhaincha) generates carbonic and organic acids during decomposition, mobilizing native calcium carbonate (CaCO3). Cultivation of sodicity-tolerant crop cultivars like CSR-30 Basmati rice and KRL-210 wheat ensures economic yields during the transitional reclamation phase.
Conclusion
Successful rehabilitation of salt-affected lands depends on tailored physical, chemical, and biological strategies. Integrating diagnostic recommendations from Soil Health Cards with schemes like PM-PRANAM and ICAR-CSSRI land reclamation models ensures sustained soil health restoration, improved water productivity, and national food security.