Soils & Agro-Climatic Zones of Bihar: Terai, Balal, Alluvial & Forest Soils
A complete scientific classification of soils in Bihar for 72nd BPSC. Terai soil, Khadar (New Alluvial), Bangar (Old Alluvial), Karail-Kewal soils, and the 3 Agro-Climatic Zones (Zone 1, 2, 3A, 3B).
1. Three Broad Soil Classifications in Bihar
Bihar’s soils are fundamentally shaped by the depositional activity of the Ganga and its tributaries, and the weathering of the Chhota Nagpur crystalline plateau. Soils are divided into: (1) North Bihar Plain Soils, (2) South Bihar Plain Soils, and (3) Southern Plateau Margin Soils.
| Zone Name | Districts Covered | Rainfall | Major Crops |
|---|---|---|---|
| Zone I (North-West Alluvial Plain) | 13 Districts (Saran, Champaran, Vaishali, Darbhanga) | 1,040 – 1,450 mm | Rice, Wheat, Sugarcane, Maize |
| Zone II (North-East Alluvial Plain) | 8 Districts (Purnea, Katihar, Saharsa, Kishanganj) | 1,200 – 1,700 mm | Jute, Maize, Pineapple, Makhana |
| Zone III-A (South-East Alluvial Plain) | 6 Districts (Bhagalpur, Banka, Munger, Jamui) | 990 – 1,250 mm | Rice, Wheat, Pulses, Mango |
| Zone III-B (South-West Alluvial Plain) | 11 Districts (Patna, Nalanda, Bhojpur, Gaya, Rohtas) | 900 – 1,150 mm | Rice, Wheat, Lentils, Gram |
2. Karail-Kewal & Tal Soils in South Bihar
Karail-Kewal soil is heavy clayey, dark grey soil found in South Bihar (Rohtas, Bhojpur, Patna, Gaya) with high moisture retention capacity, ideal for wheat and rabi pulses.
Tal soil occupies the continuous depression along the southern bank of the Ganga (8 to 10 km wide from Fatuha to Lakhisarai) which stays waterlogged during monsoons and yields bumper pulse crops in rabi season.