Soils of India

Subject: Geography | Unit: Physical Geography | Topic: Soils Exam: AP Group 2 (APPSC)

Introduction

Soil is the foundation of India's agriculture, which supports ~58% of the population. India's diverse geology, climate, and vegetation have produced eight major soil types, each with distinct properties that determine what crops can be grown. ICAR (Indian Council of Agricultural Research) classifies Indian soils, and this classification is a staple of competitive exams. Understanding soil types, their distribution, and their relationship to crops is essential for geography, agriculture, and AP-specific questions.

Context

Soil formation (pedogenesis) depends on parent rock, climate, vegetation, topography, and time. India's soils range from the highly fertile alluvial soils of the Northern Plains and coastal deltas to the nutrient-poor laterite soils of the Western Ghats. Soil degradation through erosion, salinization, and waterlogging threatens India's food security — the country loses about 5,334 million tonnes of soil every year.

Core Content

ICAR Classification: 8 Major Soil Types

Alluvial Soil (40-43% — Most Important)

• Found in Northern Plains, Narmada-Tapi valleys, and coastal plains
• Formed by depositional work of rivers
• Rich in: potash, phosphoric acid, lime
• Deficient in: nitrogen and humus
• Crops: Rice, wheat, maize, sugarcane, pulses, oilseeds

Two Subtypes:

Black Soil / Regur / Cotton Soil (15%)

• Parent rock: Cretaceous lava (basalt) — Deccan Trap region
• Area: ~5.46 lakh sq km; deep black due to titaniferous magnetite, iron, aluminium
• Develops cracks when dry (10-15 cm deep) — "self-ploughing" effect
• Extremely high moisture retention; becomes sticky when wet
• Rich in: iron, lime, calcium, potash, aluminium, magnesium
• Deficient in: nitrogen, phosphorus, organic matter
• Ideal for: Cotton (hence "cotton soil"), pulses, millets, tobacco, citrus, sugarcane

Red and Yellow Soil (18.5%)

• Found on crystalline igneous rocks in areas of low rainfall
• Color: Red (ferric oxide in topsoil), Yellow (hydrated ferric oxide in subsoil)
• Thin and poor in uplands; deeper and richer in lowlands
• Deficient in: lime, phosphate, nitrogen, humus, potash
• Crops: millets, groundnuts, potatoes, tobacco, wheat, cotton (with irrigation)

Laterite Soil (3.7-4.3%)

• Name from Latin "later" = brick (hardens like brick on air exposure)
• Formation: monsoon rains leach away lime and silica; iron oxide and aluminium remain
• Used as building material in southern India (Kerala, Karnataka)
• Rich in: iron, aluminium
• Poor in: nitrogen, potash, lime, organic matter
• Crops: rice, ragi, sugarcane, cashew, rubber, tea, coffee (with manuring)

Soil Erosion and Conservation

Types of erosion: Sheet erosion, Rill erosion, Gully erosion (ravines/badlands)

• Chambal valley ravines: classic example of gully erosion
• India loses ~5,334 million tonnes of soil every year

Conservation methods: Contour ploughing, Terrace farming, Strip cropping, Shelter belts, Afforestation, Check dams, Mulching

AP Connection

• Red soils cover most of Rayalaseema region — suited for millets, groundnut, pulses
• Black cotton soil in Guntur, Prakasam, Krishna districts — ideal for cotton and chillies
• Coastal alluvial soils in Godavari and Krishna deltas — highly fertile for rice
• Laterite soils in parts of Visakhapatnam hills — supports coffee plantations
• Sandy soils along the coastal belt — coconut and cashew cultivation
• AP's diverse soil types directly explain the regional crop patterns: rice in deltas, cotton in black soil belt, groundnut in Rayalaseema

Key Points Summary

1. ICAR classifies Indian soils into 8 major types
2. Alluvial soil covers maximum area (40-43%) and is most important for agriculture
3. Alluvial has two subtypes: Bhangar (old, kankar) and Khadar (new, fertile)
4. Black soil = Regur = Cotton soil — self-ploughing, cracks when dry, high moisture retention
5. Black soil forms from basalt lava (Deccan Trap); deficient in nitrogen and phosphorus
6. Red soil gets its color from ferric oxide (iron); found on crystalline igneous rocks
7. Laterite = "brick soil" — hardens on exposure to air; formed by leaching in heavy monsoon areas
8. Desert soil is sandy and saline but highly productive when irrigated (Indira Gandhi Canal)
9. Forest/Mountain soil has highest organic matter (40-50% humus)
10. Saline/Alkaline soils have white salt crust; local names: Reh, Kallar, Usar
11. Peaty/Marshy soils are waterlogged with high organic matter
12. India loses ~5,334 million tonnes of soil annually to erosion
13. Chambal valley = classic gully erosion example
14. Conservation methods include contour ploughing, terrace farming, and shelter belts
15. In AP: Red soil (Rayalaseema), Black soil (Guntur-Krishna), Alluvial (deltas)

Exam Strategy

• Most asked: Alluvial > Black > Red > Laterite in exam frequency
• Comparison questions: Bhangar vs Khadar, Black vs Red, Alluvial vs Laterite
• Association-based: Black soil = cotton = self-ploughing = Deccan Trap = basalt
• AP-specific: Know soil distribution by district — red in Rayalaseema, black in Guntur-Prakasam, alluvial in deltas
• Trick: Alluvial soil is deficient in NITROGEN (not potash — it is rich in potash)

Key Terms Glossary