Reclamation and Management of Problematic Soils

Introduction

Problematic soils exhibit severe physical, chemical, or biological constraints that render crop cultivation uneconomical without targeted interventions. According to the ICAR-Central Soil Salinity Research Institute (ICAR-CSSRI), India currently faces approximately 6.74 million hectares of salt-affected soils alone. Achieving long-term soil productivity necessitates an integrated triad of chemical amendments, physical soil modifications, and biological interventions.

1. Chemical Constraints and Quantitative Reclamation

• Sodic/Alkali Soils (ESP > 15%, pH > 8.5): Characterized by excess exchangeable sodium causing soil dispersion, deflocculation, and impaired aeration.
  • Reclamation Principle: Replacement of exchangeable sodium by calcium: Na₂-[Soil Clay] + CaSO₄ (Gypsum) → Ca-[Soil Clay] + Na₂SO₄ ↓ (leached)
  • Quantitative Assessment: Amendment volume is determined by the Gypsum Requirement (GR), calculated based on the soil Cation Exchange Capacity (CEC) and the difference between initial and desired Exchangeable Sodium Percentage (ESP).
• Saline Soils (EC > 4 dS/m): Characterized by high concentrations of soluble salts exerting severe osmotic stress on crops.
  • Reclamation Principle: Establishment of Sub-Surface Drainage (SSD) networks to lower the water table and interrupt capillary rise, followed by ponding and leaching.
  • Quantitative Assessment: The depth of water required to flush excess salts is given by the Leaching Requirement (LR): LR = EC_iw / EC_dw (where EC_iw is the electrical conductivity of irrigation water and EC_dw is the electrical conductivity of drainage water).
• Acid Soils (pH < 5.5): Suffer from aluminum and manganese toxicity alongside phosphorus fixation.
  • Reclamation Principle: Neutralization using agricultural lime: H₂-[Soil Clay] + CaCO₃ (Lime) → Ca-[Soil Clay] + H₂O + CO₂ ↑
  • Quantitative Assessment: Lime requirement (LR) is quantified using buffer methods such as the Shoemaker-McLean-Pratt (SMP) method.

2. Physical Constraints and Field-Scale Agronomic Interventions

• Heavy Clays and Low Permeability: Amending dense clay textures with sand is economically unviable at field scale. Viable engineering and agronomic solutions include Broad Bed and Furrow (BBF) systems, deep chisel ploughing (sub-soiling) to fracture subterranean hardpans, and large-scale incorporation of organic residues to improve aggregate porosity.
• Surface Crusting (e.g., Red Alfisols): Impedes seedling emergence due to rapid drying and structural breakdown. Remediation involves shallow tooth-harrowing, surface mulching with farmyard manure (FYM) or coir pith at 12.5 tonnes/ha, and increased seeding rates to facilitate collective mechanical emergence.
• Shallow Soils: Depth-restricted soils cannot support deep-rooted taproot systems. Recommended interventions include planting hardy, shallow-rooted species (such as minor millets and horsegram), constructing half-moon terraces on slopes, and employing deep-pitting techniques for horticultural crops.

3. Biological Constraints and Varietal Innovations

• Biological Degradation: Characterized by depleted Soil Organic Carbon (SOC < 0.5%), suppressed beneficial microflora, and parasitic nematode accumulation. Managed via in-situ green manuring with Sesbania aculeata (Dhaincha), halophilic bio-inoculants, and vesicular-arbuscular mycorrhizal (VAM) fungi.
• Stress-Tolerant Cultivars: Developed by ICAR-CSSRI to facilitate biological reclamation while sustaining economic yields:
  • Wheat: KRL-210, KRL-386
  • Rice: Basmati CSR-30, CSR-104
  • Mustard: CS-62

Conclusion

Reclaiming problematic soils requires moving beyond isolated chemical applications to an Integrated Soil Health Management (ISHM) approach. Combining stress-resilient cultivars with policy mechanisms such as the Soil Health Card Scheme and targeted central schemes for alkali soil reclamation is essential for achieving India's Land Degradation Neutrality targets under SDG 15.3.