Reclamation of Acid Soils
Definition: Soils with pH < 6.5 due to leaching of bases and accumulation of Fe³⁺, Al³⁺, Mn²⁺.
Problems
- Toxicity: Al, Mn, Fe.
- Deficiency: Ca, Mg, P, Mo.
- Poor microbial activity & root growth.
Reclamation Methods
- Liming (main practice)
- Neutralizes soil acidity.
- Materials: Calcium carbonate (CaCO₃ – agricultural lime). Dolomite (CaMg(CO₃)₂). Quick lime (CaO). Slaked lime (Ca(OH)₂)
- Lime requirement calculated by Shoemaker–McLean–Pratt (SMP) buffer method.
- Organic amendments; Farmyard manure, compost, green manures → increase microbial activity & buffer capacity.
- Subsoil acidity management; Gypsum application improves Ca supply.
- Crop management; Grow acid-tolerant crops: Rice, potato, tea, pineapple, ryegrass.
- Reclamation of Saline Soils
Definition: Soils with EC > 4 dS/m, pH < 8.5, ESP < 15 (high soluble salts).
Problems
- High osmotic pressure → poor seed germination.
- Toxicity: Na⁺, Cl⁻, SO₄²⁻.
- Deficiency of Ca, K, micronutrients.
Reclamation Methods
- Leaching of salts; Apply good quality irrigation water + proper drainage. Leaching Requirement (LR) = minimum water needed to remove salts.
- Drainage: Essential for removing excess salts from root zone.
- Amendments (if sodium salts present): Gypsum (CaSO₄·2H₂O) replaces Na⁺ with Ca²⁺. Sulphur, sulphuric acid, iron pyrite.
- Crop management: Grow salt-tolerant crops: Barley, sugar beet, cotton, rice (CSR varieties). Use salt-tolerant varieties: CSR-10, CSR-23 (rice), KRL-19 (wheat).
2. Reclamation of Sodic (Alkali) Soils
Definition: Soils with
- ESP > 15
- pH > 8.5
- EC < 4 dS/m
Problems
- High exchangeable sodium → dispersion of clay, poor structure.
- Hard crust on drying, poor infiltration, low permeability.
- Deficiency: Ca, Zn, Fe.
- Toxicity: Na⁺, HCO₃⁻, CO₃²⁻.
- Poor seed germination, low microbial activity.
Reclamation Methods
- Chemical Amendments
- Gypsum (CaSO₄·2H₂O) → most common & effective.
- Others: Pyrite (FeS₂), Sulphur, Sulphuric acid, Iron sulphate.
- Mechanism: Ca²⁺ replaces Na⁺ from exchange complex → Na⁺ leached.
- Leaching: Essential after amendment to remove displaced Na⁺ salts.
- Organic Amendments; FYM, compost, green manures → improve microbial activity, CO₂ production (helps solubilize CaCO₃).
- Crop Management; Grow sodicity-tolerant crops: Rice, barley, cotton. Use tolerant varieties: KRL-1-4, KRL-19, CSR-36 (wheat).
3. Reclamation of Saline-Sodic Soils
Definition: Soils with
- EC > 4 dS/m
- ESP > 15
- pH variable (7.5–8.5 or higher depending on salts)
Problems; Contain both excess soluble salts (salinity) and exchangeable sodium (sodicity). High osmotic pressure + poor soil structure. Plant growth severely restricted.
Reclamation Methods
- Amendments
- Gypsum → supplies Ca²⁺ to replace Na⁺.
- Sulphur, sulphuric acid, iron pyrite → convert native CaCO₃ into available Ca²⁺.
- Leaching with good quality water; Removes excess salts along with displaced Na⁺. Proper drainage is essential.
- Crop Management; Salt-tolerant crops (barley, sugar beet, cotton). Rice–wheat system works well in reclaimed soils.
4. Reclamation of Calcareous Soils
Definition: Soils containing >10–15% free CaCO₃, pH 7.5–8.5. Common in arid & semi-arid regions.
Problems
- High CaCO₃ leads to:
- Phosphorus fixation → P deficiency.
- Micronutrient deficiencies: Fe, Zn, Mn.
- Low availability of N (due to ammonia volatilization).
- Poor response to fertilizers.
Reclamation Methods
- Fertilizer Management: Use acid-forming fertilizers: Ammonium sulphate, Urea, SSP (Single Superphosphate). Avoid lime-containing fertilizers.
- Micronutrient Application: ZnSO₄ for zinc deficiency. FeSO₄ or Fe-chelates for iron deficiency. Foliar spray of Fe/Zn is effective.
- Organic Amendments: FYM, compost → increase microbial activity & availability of P and micronutrients.
- Green Manuring & Crop Choice: Green manure crops like Dhaincha improve soil properties. Grow tolerant crops: sorghum, maize, pearl millet.
Reclamation of Waterlogged Soils
Definition: Soils where water table is within 2 m of surface → anaerobic condition.
Problems
- Poor aeration, root respiration inhibited.
- Accumulation of toxic substances (Fe²⁺, Mn²⁺, H₂S).
- Nitrogen loss (denitrification, leaching).
- Yield decline in sensitive crops (wheat, pulses).
Reclamation Methods
- Engineering Measures (Most effective)
- Surface drainage (open ditches, furrows).
- Sub-surface drainage (tile drains, perforated pipes).
- Pumping out groundwater (tubewells).
- Biological/Bio-drainage; Planting deep-rooted, high water-use trees: Eucalyptus, Poplar.
- Agronomic Practices; Ridge & furrow planting. Raised bed cultivation. Selection of waterlogging-tolerant crops: Rice, jute, sugarcane.
- Chemical Management; Application of gypsum or lime in sodic-waterlogged soils. Controlled irrigation scheduling to avoid standing water.
Key Points for ASRB NET
- Sodic soils → Amendments (Gypsum) + Leaching
- Saline-sodic soils → Amendments (Gypsum) + Leaching + Drainage
- Calcareous soils → Acid-forming fertilizers + Micronutrients (Zn, Fe) + Organic matter
- Waterlogged soils → Drainage (engineering) + Bio-drainage + Tolerant crops
