Introduction
Problematic soils are soils that possess severe inherent physical, chemical, or biological constraints that render them uneconomical and unsuitable for normal crop cultivation without targeted reclamation measures. According to data from the ISRO Desertification and Land Degradation Atlas (2021) and ICAR, between 97.85 and 120.7 million hectares of India's geographical area suffer from degradation, posing significant risks to national food and nutritional security.
1. Chemical Constraints and Reclamation
- Acidic Soils (pH < 5.5): Characterized by aluminum (Al), iron (Fe), and manganese (Mn) toxicity, alongside severe fixation and deficiency of phosphorus and molybdenum.
- Reclamation: Neutralization through agricultural lime (CaCO₃) or dolomite. The reaction proceeds as: Clay-2H⁺ + CaCO₃ → Clay-Ca²⁺ + H₂O + CO₂↑.
- Agronomic Interventions: Application of basic slag, rock phosphate, and cultivation of acid-tolerant crops like tea and potato.
- Sodic / Alkali Soils (pH > 8.5, ESP > 15%, EC < 4 dS/m): Characterized by excessive exchangeable sodium causing clay dispersion, deflocculation, surface crusting, and poor hydraulic conductivity.
- Reclamation: Chemical replacement of exchangeable sodium using gypsum (CaSO₄·2H₂O) or iron pyrites: Clay-2Na⁺ + CaSO₄ → Clay-Ca²⁺ + Na₂SO₄ (subsequently removed by leaching).
- Agronomic Interventions: Incorporation of organic amendments, green manuring (Dhaincha - Sesbania aculeata), and growing tolerant crops like barley and Karnal grass.
- Saline Soils (EC > 4 dS/m, pH < 8.5, ESP < 15%): Dominated by soluble neutral salts (chlorides and sulfates of sodium, calcium, and magnesium), resulting in high osmotic pressure, physiological drought, and specific ion toxicity.
- Reclamation: Mechanical flushing and leaching of soluble salts beyond the root zone using good quality irrigation water, facilitated by subsurface tile drainage systems (CSSRI model). Chemical amendments are ineffective here.
- Agronomic Interventions: Use of salt-tolerant cultivars (e.g., Wheat KRL-210, CSR-10 rice) and furrow planting.
2. Physical Constraints and Reclamation
- Subsurface Hardpan and Soil Compaction: Dense layers restrict vertical root penetration, reduce aeration, and impede infiltration.
- Reclamation: Deep chiseling or subsoiling up to 50 cm depth once every three years; biological perforation using deep tap-rooted crops such as pigeon pea (Cajanus cajan).
- Surface Crusting: Common in sesquioxide-rich red and lateritic soils following rainfall events, which hampers seedling emergence.
- Reclamation: Shallow intercultural operations (blind harrowing), surface mulching, incorporation of farmyard manure (FYM) or coir pith, and utilizing higher seeding rates.
- Excessive Permeability / Coarse Sandy Soils: Extremely high percolation rates cause severe nutrient leaching and poor moisture retention.
- Reclamation: Compaction with heavy rollers at optimum moisture, application of tank silt, and bentonite clay lining.
3. Biological Constraints and Reclamation
- Low Soil Organic Carbon (SOC < 0.5%): Severely suppresses biological activity and microbial nutrient mineralization.
- Reclamation: Conservation agriculture practices (zero tillage, permanent soil cover), green manuring with Sesbania, and in-situ residue retention using equipment like the Happy Seeder.
- Soil Sickness and Pathogen Buildup: Monocropping and indiscriminate agrochemical use deplete beneficial rhizosphere flora while fostering soil-borne pathogens and plant-parasitic nematodes.
- Reclamation: Diverse crop rotations, biofumigation with brassica cover crops, inclusion of antagonistic trap crops like marigold (Tagetes spp.), and bio-inoculants such as Trichoderma and Vesicular Arbuscular Mycorrhizae (VAM).
Conclusion
Reclamation of problematic soils necessitates a paradigm shift from ad-hoc chemical treatments toward Integrated Soil Health Management. Leveraging diagnostic frameworks such as the Soil Health Card alongside policy interventions like PM-PRANAM and India's Bonn Challenge commitment to restore 26 million hectares of degraded land by 2030 will be crucial for securing Land Degradation Neutrality under SDG 15.3.