The soil of Bihar exhibits considerable variation. The alluvial soil deposited by the rivers is a prominent soil type, primarily found in the north and eastern parts of the state. The alluvial soil is composed of fine silt, clay, and sand and is generally fertile and suitable for agriculture.

In the southern and western regions of Bihar, especially in the Chhotanagpur plateau and Kaimur plateau, red soil and lateritic soil dominate. These soils are typically reddish in color and have a higher concentration of iron oxide and aluminum oxide. While red soils have a sandy texture, lateritic soils are more clayey and less fertile compared to alluvial soils.

Additionally, in the Terai region of Bihar, which lies along the foothills of the Himalayas, there is a presence of Terai soil. This soil is a mix of alluvial and forest soil, characterized by its high organic content and suitability for agriculture.

Overall, the soil of Bihar can be classified into three major types: alluvial soil, red soil, and lateritic soil, with variations in texture, composition, and fertility.