Saline, Alkali and Acid Soils

Saline, Alkali and Acid Soils: Classification, Characteristics, and Reclamation

Understanding problem soils—saline, alkali (sodic), saline-alkali, and acid soils—is essential for sustainable agriculture and soil health management in India. These soils reduce crop productivity, degrade land quality, and require specialized management. This post explores their causes, properties, reclamation techniques, and comparative differences—vital for both students and farmers.

What are Saline and Alkali Soils?

Saline and alkali soils contain excessive amounts of soluble salts or exchangeable sodium. These salts are often chlorides (Cl⁻), sulfates (SO₄²⁻), carbonates (CO₃²⁻) and bicarbonates (HCO₃⁻) of sodium (Na⁺), calcium (Ca²⁺), and magnesium (Mg²⁺).

1. Saline Soils (White Alkali)

🔸 Characteristics:

• EC (Electrical Conductivity): > 4.0 dS/m at 25°C
• ESP: < 15%
• pH: < 8.5
• High concentrations of NaCl and Na₂SO₄
• White salt crust on surface (hence, white alkali)
• Flocculated structure → good aeration and permeability

🔸 Formation:

• Occurs in arid/semi-arid regions (Rainfall < 55 cm)
• Sources: Irrigation water, high water table, sea water, canal seepage

🔸 Reclamation:

• Leaching with good quality water
• Ensure proper drainage
• Use of intermittent ponding is more efficient than continuous ponding
• Crop: Rice is preferred in initial years

2. Alkali Soils (Sodic or Black Alkali)

🔸 Characteristics:

• EC: < 4.0 dS/m
• ESP: > 15%
• pH: 8.5–10
• Low infiltration rate
• Black color due to dispersed organic matter
• Dispersed and compact → poor aeration and water movement

🔸 Formation:

• Formed in regions with 55–90 cm rainfall
• Three stages:
  1. Salination
  2. Saline-Alkali formation
  3. Alkalization

🔸 Reclamation:

• Replace Na⁺ with Ca²⁺ using chemical amendments:
  • Gypsum (CaSO₄·2H₂O)
  • Iron Pyrite (FeS₂)
  • Sulfur, acids, or acid-forming materials
• Use of organic manures, green manures (e.g., Dhaincha)
• Leaching to remove released sodium salts
• Apply Zinc and higher doses of Nitrogen

🔸 Cropping System:

• Rice-Dhaincha (U.P.)
• Dhaincha–Rice–Berseem (Punjab)

3. Saline-Alkali Soils

🔸 Characteristics:

• EC: > 4.0 dS/m
• ESP: > 15%
• pH: < 8.5
• Difficult to manage due to poor structure and drainage

🔸 Causes:

• Aridity, poor drainage, use of brackish water
• Fluctuating water table
• Improper irrigation practices (e.g., alternating flooding and drought)

🔸 Reclamation:

• Combination of amendments + leaching + drainage
• Organic matter enhances microbial activity and soil structure

4. Acid Soils

Acid soils are covered in a separate topic. Briefly:

🔸 Characteristics:

• pH: < 5.5
• Common in high rainfall areas (Northeast, Western Ghats)
• Toxic levels of Al³⁺ and Mn²⁺
• Deficiency of Ca, Mg, P, Mo

🔸 Management:

• Application of lime (CaCO₃) or dolomite
• Use of acid-tolerant crops
• Organic manure to buffer pH

Key Differences: Saline vs. Alkali Soils

USAR Soils and Mechanical Reclamation

USAR soils are degraded sodic soils, mainly in Uttar Pradesh (1.2 million ha) and parts of Punjab & Haryana.

Mechanical Methods:

1. Scraping of salt crust
2. Leaching (only if water table > 3 m and no hardpan)
3. Flushing (washing remaining salts)
4. Ditching/Trenching
5. Drainage systems (to lower water table)

Agricultural Practices for Salt-Affected Soils

• Use salt-tolerant varieties
• Apply gypsum + organic manure
• Adopt crop rotation: Rice–Dhaincha, Dhaincha–Berseem
• Improve drainage systems
• Promote frequent light irrigation
• Green manuring improves physical condition and supplies weak organic acids

For Competitive Exams:

• Definitions of ESP, SAR
• Soil classification by EC, pH, ESP
• Differences between saline, alkali, and saline-alkali soils
• Reclamation methods: chemical, mechanical, and biological
• Regions affected in India (e.g., U.P., Punjab, Haryana)
• Soil amendments (gypsum, sulfur, FeS₂)
• Recommended cropping systems and salt-tolerant crops