Soils of Bihar

Introduction

• Soil is a key natural resource supporting agriculture, industry, and overall economic activity.
• Bihar’s plains rest on a thick alluvial cover, deposited over time by rivers from the Himalayas.
• Most soils here are young alluvial loams, rejuvenated annually by fresh silt, sand, and clay.
• Deficient in: Nitrogen, Phosphoric acid, Humus
• Adequate in: Potash and Lime

Major Soil Types in Bihar

Bihar has three main soil categories:

1. Piedmont Swamp Soil

• Found in: North-western West Champaran
• Formed in low-lying, swampy piedmont zones below the Siwaliks.
• High moisture, clayey texture.
• Very suitable for paddy cultivation.

2. Terai Soil

• Found along: Indo-Nepal border (northern Bihar)
• Formed where underground Bhabar streams reappear.
• Features:
  • Poorly drained, moist, silty, rich in organic matter
  • High in nitrogen, low in phosphate
• Supports crops like: Rice, Wheat, Sugarcane, Jute
• Region naturally hosts tall grasses & dense forests.

3. Gangetic Alluvial Soil

Covers almost the entire Bihar plain; the most important soil type.

Formation

• Deposited by rivers of the Indo-Gangetic system
  (Ganga, Ghaghara, Gandak, Kosi, Son, Mahananda, Bagmati)

Characteristics

• Young, porous, loamy soils with weak profile development.
• Mostly sandy loam to clay loam.
• Kankar (lime nodules) common in older alluvium.
• Excellent fertility — constantly renewed by floods.

Chemical Nature

• Low nitrogen
• Adequate potash, phosphates, and alkalies
• Variable iron oxide and lime

Crops

• Highly productive for:
  Rice, Wheat, Maize, Lentils, Sugarcane, Jute, Tobacco, Oilseeds, Vegetables, Fruits

Sub-Types of Alluvial Soils

(a) Bhangar (Older Alluvium)

• Found on higher terraces above flood plains.
• Darker, more clayey.
• Contains kankar layers a few meters below the surface.

(b) Khadar (Newer Alluvium)

• Found on the active floodplains.
• Replenished annually by river floods.
• Lighter, sandy, highly fertile — best for agriculture.

Key Features of Bihar’s Soil Profile

• Formed mostly by riverine deposition.
• Soil fertility varies but is generally high.
• Agriculture in Bihar thrives because soils respond well to irrigation.
• Soil diversity allows cultivation of both Kharif & Rabi