Rajasthan Saline & Alkaline Soils GK

PART - 16: Saline & Alkaline Soils of Rajasthan#

Detailed Index#

📖 16.1 Chemical Diagnostics & Triangular Classification

According to the standards of Pedology and the United States Salinity Laboratory (USSL, Riverside), Salt-Affected Soils are classified into three distinct categories based on their three main chemical parameters—Electrical Conductivity (EC), Exchangeable Sodium Percentage (ESP), and Soil Reaction (pH value):

📖 16.2 Detailed Chemical Differences (Saline vs Alkaline)

                     [Salt-Affected Soils]
                              │
        ┌─────────────────────┴─────────────────────┐
        ▼                                           ▼
[1. Saline Soil (White Alkali)]              [2. Alkaline Soil (Black Alkali)]
 • Main Salts: NaCl, Na₂SO₄, CaCl₂, MgSO₄    • Main Salts: Na₂CO₃, NaHCO₃
 • Surface White Crust (White efflorescence)  • Dark Brown/Black Color (Humus dissolution)
 • Soil particles remain Flocculated          • Soil particles become Dispersed
 • Physical water permeability normal         • Permeability & aeration completely blocked
 • Reclamation: Leaching with fresh water     • Reclamation: Chemical amendments (Gypsum, Pyrite)

1. Saline Soil (Solonchak)#

2. Alkaline/Sodic Soil (Solonetz) / क्षारीय#

📖 16.3 Local Nomenclature & Terminology

Traditional terminology used for saline and alkaline soils in various regions of Rajasthan:

📖 16.4 Geological Causes of Salinity & Alkalinity

The formation of salt-affected soils in Rajasthan is not only a result of natural processes, but human-induced canal indiscretion is also responsible for it:

                  [5 Primary Sources of Salinity Formation]
                                  │
   ┌────────────────┬─────────────┼────────────────┬────────────────┐
   ▼                ▼             ▼                ▼                ▼
[Remnants of    [Climatic       [Canal Waterlogging: [From Saline    [Saline Water
 Tethys Sea     Evaporation]     'Sem' Problem]      Groundwater]    from Rann of Kutch]
 Rocks]

1. Palaeo-geographic Remnants (Tethys Sea) / पुरा-भौगोलिक अवशेष#

• Western Rajasthan has been geologically a part of the Tethys Geosyncline.
• Natural deposits of Mica-schist and marine salts exist in the subsurface rocks. During weathering, these salts continue to dissolve in groundwater and soil.

2. Arid Climate & Rapid Capillary Action#

• Average annual rainfall in western Rajasthan is only 10-30 cm, while Potential Evapotranspiration (PET) rate is more than 200 cm.
• Due to low rainfall, salts cannot leach downward. In summer, when the surface becomes extremely hot, subsurface moisture is drawn toward the surface through capillary tubes. Water evaporates and the dissolved salts are left behind on the surface as a white crust.

3. 'Sem' (Waterlogging) Problem in Canal Command Areas / नहरी कमान क्षेत्रों में 'सैम' की समस्या#

4. Continuous Irrigation with Saline & Alkaline Groundwater / खारे एवं लवणीय भू-जल द्वारा निरंतर सिंचाई#

• About 60-70% of tube wells and wells in western and central Rajasthan (Jodhpur, Nagaur, Barmer, Pali, Jalore) have saline or alkaline water (EC > 4 dS/m, RSC > 2.5 meq/L).
• Repeated use of this water causes soluble sodium ions to deposit on soil clay particles, turning fertile fields into alkaline Usar.

5. Marine Winds & Tidal Flow from Rann of Kutch#

• Border areas of Sanchore, Barmer, and Jalore are connected to the Rann of Kutch. South-west monsoon winds carry marine salt particles and deposit them on the surface.

📖 16.5 Spatial Distribution in Rajasthan

About 3.74 lakh hectares of land in Rajasthan is severely affected by salinity and alkalinity:

📖 16.6 Adverse Impacts on Soil Health & Plant Physiology

Biological crises arising from concentration of salts and sodium in soil:

[Increase in Salt Concentration] ──> [Osmotic Pressure of Soil Solution becomes very high]
                                              │
               ┌──────────────────────────────┴──────────────────────────────┐
               ▼                                                             ▼
[Physiological Drought]                                    [Specific Ion Toxicity]
 • Roots cannot absorb even when water is present           • Concentration of Na⁺, Cl⁻, BO₃³⁻ in cells
 • Endosmosis stops; exosmosis causes plant to dry          • Tip burn of leaves

📖 16.7 Scientific Reclamation Measures

A. Reclamation of Saline Soil — Physical Methods#

Since salts in saline soil are water-soluble, their reclamation is done only through water management without chemicals:

B. Reclamation of Alkaline/Sodic Soil — Chemical Amendments#

To remove exchangeable sodium (Na⁺) from alkaline soil, use of chemical amendments providing divalent calcium (Ca²⁺) ions is essential:

[Alkaline Soil: Na⁺ adsorbed on clay] + [Gypsum: CaSO₄·2H₂O]
                         │
                         ▼ (Ion Exchange Reaction)
[Reclaimed Soil: Ca²⁺ adsorbed on clay] + [Sodium Sulphate: Na₂SO₄ (water-soluble salt)]
                         │
                         ▼ (Leaching / Drainage by irrigation water)
              [Na₂SO₄ flows out of the field]

1. Use of Gypsum (CaSO₄·2H₂O) — Best & Most Common#

• Mechanism: Calcium (Ca²⁺) present in gypsum displaces harmful sodium (Na⁺) sitting on soil particles and attaches itself. The displaced sodium forms water-soluble sodium sulphate (Na₂SO₄), which is washed away by leaching:

$$2Na\text{-Clay} + CaSO_4 \rightleftharpoons Ca\text{-Clay} + Na_2SO_4 \downarrow$$

• Rajasthan Government provides heavy subsidy on gypsum to farmers for alkaline land reclamation.

2. Use of Iron Pyrites (FeS₂)#

• Suitability: In those alkaline soils where limestone (CaCO₃) is already naturally present.
• Mechanism: Pyrites reacts with air and water in soil to form sulphuric acid (H₂SO₄), which converts insoluble lime in soil into active calcium.

C. Biological & Agronomic Measures#

📖 16.8 Salt-Tolerant Crops & Varieties

In salt-affected areas, salt-resistant species are selected instead of normal crops:

📖 16.9 Institutional Efforts & Specific Projects

📖 16.10 Key Exam Pointers

Exam Revision#

Saline Soil: pH < 8.5, EC > 4.0 dS/m, ESP < 15%, Solonchak, White Usar (NaCl, Na₂SO₄) -> Alkaline Soil: pH > 8.5, EC < 4.0 dS/m, ESP > 15%, Solonetz, Black Usar (Na₂CO₃ dissolves humus) -> Geological Causes: Tethys Sea remnants, arid capillary action, Sem problem (Badopal, Hanumangarh) -> Soil Reclamation: Gypsum ($CaSO_4 \cdot 2H_2O$) for Alkaline soils ($$2Na\text{-Clay} + CaSO_4 \rightleftharpoons Ca\text{-Clay} + Na_2SO_4 \downarrow$$), Leaching & Sub-surface Drainage (SSD) for Saline soils -> Green Manure: Dhancha (Sesbania aculeata, acidic sap pH ≈ 4.0) -> Salt-Tolerant Crops: Barley (Jau - most tolerant cereal), Kharchia-65 wheat, Sugarbeet -> Institutions: RAJAD Project (Kota CAD with Canada CIDA), CSSRI Karnal, CAZRI Jodhpur -> 16.10 Comparative Study

AI-Friendly Tags#

rajasthan-gk, rajasthan-soils, saline-soils, alkaline-soils, solonchak, solonetz, gypsum-reclamation, dhancha-green-manure, sem-problem, badopal-hanumangarh, rajad-project, cssri, cazri, comparative-study