Soil Types of the Andaman & Nicobar Islands: A Tropical Pedology Guide

The Andaman and Nicobar Islands, an Indian archipelago in the Bay of Bengal, exhibit a soil mosaic shaped by volcanic geology, intense tropical weathering, coastal dynamics, and dense forest cover. Three primary soil groups dominate, with localized variants adding complexity.

1. Laterite Soils (Dominant in Uplands)

• Formation: Intense chemical weathering of basalts and other mafic/ultramafic rocks under high temperature and rainfall (>3,000 mm/yr).
• Characteristics: Red to reddish-brown; high iron/aluminum oxides (Fe₂O₃, Al₂O₃); low silica; acidic (pH 4.5–5.5); well-drained, porous, good aeration.
• Fertility: Low inherent fertility—nutrient leaching is severe. Respond well to liming, organic matter, and balanced fertilization.
• Distribution: Hilly interiors, elevated plateaus, sloping terrain across both island groups.

2. Alluvial Soils (Coastal & Valley Floors)

• Formation: Fluvial deposition by streams and rivers; marine alluvium in tidal zones.
• Characteristics: Gray to dark brown; stratified texture (sand, silt, clay); neutral to slightly acidic; good water-holding capacity; high organic matter in older deposits.
• Fertility: Most agriculturally productive soils in the islands. Support coconuts, areca nut, banana, rice, vegetables, spices (cinnamon, nutmeg, clove, black pepper).
• Distribution: Coastal plains, river valleys, low-lying areas near creek mouths.

3. Beach Sands (Littoral Zones)

• Composition: Quartz, coral fragments, shell debris, heavy minerals; coarse, single-grained.
• Properties: Excessively drained; very low water/nutrient retention; saline; alkaline near shore.
• Agricultural suitability: Poor without major amendments (organic matter, clay, irrigation). Coconut palms tolerate them best.
• Distribution: Active beaches, dune systems, raised coral reefs.

Minor but Notable Soil Types

• Black Cotton Soils (Vertisols): Clay-rich, shrink-swell, in depressed basins; high fertility but difficult tillage.
• Peat/Muck Soils: Organic-rich, waterlogged swamps (e.g., Saddle Peak area, Great Nicobar).
• Saline/Alkaline Soils: Tidal flats, mangrove margins; require reclamation for cultivation.

Agricultural Implications

The islands' farming systems reflect soil geography: plantation crops (coconut, areca nut, spices) dominate coastal alluvials and amended laterites; root crops (cassava, sweet potato, taro) and fruit trees (mango, papaya, jackfruit) occupy mid-slopes; paddy rice is confined to terraced valley bottoms with water control. Shifting cultivation (jhum) by indigenous communities (Shompen, Nicobarese) persists in interior forests.

Soil conservation is critical—steep slopes, intense rainfall, and seismic vulnerability (2004 tsunami altered coastal soils dramatically) demand terracing, contour planting, and mangrove buffer preservation.