Traditional Classification of Indian Soils

(Based on Ancient Indian Agricultural Knowledge & Observations)

Before scientific systems like USDA Soil Taxonomy were introduced, Indian farmers and early scientists classified soils using visible characteristics such as color, texture, origin, fertility, and response to crops. This indigenous system is still relevant for agronomic planning and local crop adaptation.

Major Soil Types in Traditional Indian Classification

1. Alluvial Soils

• Most extensive soil type in India (~43% of area)
• Formed by: Sedimentation by rivers (Ganga, Brahmaputra, Indus)
• Types:
  • Khadar: New alluvium, sandy, fertile, light-colored
  • Bhangar: Old alluvium, clayey, dark, contains kankar
• Fertility: Rich in potash; poor in nitrogen and phosphorus
• pH: Neutral to slightly alkaline
• Regions: Indo-Gangetic plains, coastal areas
• Important Crops: Wheat, rice, sugarcane, jute, oilseeds

2. Black Soils (Regur Soils or Cotton Soils)

• Formed from: Weathering of basaltic lava (Deccan Trap)
• Color: Deep black due to high Fe, Al & organic content
• Texture: Fine-textured, clayey
• Rich in: Ca, Mg, lime, iron
• Poor in: Nitrogen, phosphorus
• Swelling/shrinkage: Cracks during summer; sticky in rains
• Clay Mineral: Montmorillonite (high CEC)
• pH: Neutral to slightly alkaline
• Regions: Maharashtra, Gujarat, M.P., A.P., Karnataka, Tamil Nadu
• Important Crops: Cotton, sorghum, soybean, pulses

3. Red Soils

• Formed from: Weathering of crystalline igneous rocks
• Color: Red due to ferric oxide (Fe₂O₃)
• Texture: Loamy to sandy
• Poor in: Nitrogen, phosphorus, humus
• Mineral Type: Kaolinitic clay (low CEC)
• pH: Slightly acidic to neutral (6.5–7.5)
• Silica:Sesquioxide Ratio: ~2.0 (medium weathering)
• Regions: Tamil Nadu, Karnataka, Andhra Pradesh, Chhattisgarh, Jharkhand, M.P., eastern U.P.
• Important Crops: Groundnut, millets, pulses, vegetables

4. Laterite Soils

• Formed under: Tropical climate with heavy rainfall
• Process: Intense leaching removes silica, leaving oxides of Fe and Al
• Texture: Porous, gravelly
• Color: Red to yellow
• Minerals: Gibbsite (Al(OH)₃), Goethite (FeO(OH))
• Poor in: Lime, Mg, N, P
• Rich in: Fe and Al oxides
• pH: Acidic
• Regions: Western Ghats, Eastern Ghats, Kerala, Odisha, Assam
• Important Crops: Tea, coffee, cashew (with management)

5. Desert Soils (Arid Soils)

• Found in: Arid and semi-arid regions
• Texture: Sandy to loamy; low clay content
• Color: Light grey to yellowish brown
• Rich in: Salts (NaCl, CaCO₃)
• Poor in: Humus, nitrogen, moisture
• Structure: Loose and open
• Regions: Rajasthan, Haryana, Punjab, Gujarat
• Important Crops: Pearl millet, cluster bean, mustard (with irrigation)

6. Forest and Hill Soils

• Formed under: Forest cover and hilly terrain
• High in: Organic matter (O.M.)
• Texture: Loamy and silty
• Fertility: Moderate; depends on vegetation and slope
• pH: Acidic in high rainfall areas
• Regions: Himalayan states, Western and Eastern Ghats
• Important Crops: Tea, spices, temperate fruits

7. Peaty and Marshy Soils

• Formed in: Waterlogged conditions
• Color: Dark, almost black
• Rich in: Organic matter (peat), acidic
• Regions: Kerala (Kuttanad), coastal W.B., parts of Bihar
• Used for: Rice cultivation (requires proper drainage)

8. Saline and Alkaline Soils

• Found in: Poorly drained areas or with high evaporation
• White crust of salts on surface (sodium chloride, carbonate, sulfate)
• pH: > 8.5 (alkaline)
• Poor permeability and structure
• Regions: Western U.P., Punjab, Gujarat, Rajasthan
• Management: Gypsum application, leaching, drainage

Summary Table: Traditional Soil Classification

Important Facts for Exams

• Khadar: New alluvium; fertile
• Bhangar: Older alluvium; contains kankar
• Regur soils are rich in montmorillonite clay (high CEC)
• Red soils warm up faster → known as early soils
• Laterite soils are highly leached → poor in bases
• Peaty soils are acidic and organic-rich
• Saline-alkaline soils → reclamation by gypsum
• Traditional system is still used for field-level planning

Modern Classification of Soils (USDA Soil Taxonomy)

(Also known as the 7th Approximation System – 1975)

Introduction to Soil Taxonomy

The USDA Soil Taxonomy, developed and released in 1975 (based on the 7th Approximation), is a scientific, hierarchical system for classifying soils based on measurable and observable properties, rather than on how the soil formed (genesis).

Salient Features of Soil Taxonomy

Six Hierarchical Categories in Soil Taxonomy

The 12 Soil Orders in Soil Taxonomy

Application of Soil Orders in India

Key Points for Competitive Exams

• Soil Taxonomy was developed by USDA in 1975
• Based on measurable soil properties (not genesis)
• 12 soil orders – Each based on diagnostic horizons
• India primarily has 7 out of 12 orders
• Vertisols = Montmorillonitic black soils (high shrink–swell)
• Oxisols = Highly leached lateritic soils
• Histosols = Organic matter-rich swampy soils
• Spodosols, Andisols, Gelisols – Not found in India
• Entisols & Inceptisols are most widespread in India (young soils)