Alluvial soil (locally known as Kachari soil) is found all over this region except the hilly areas ofWest Champaran in Shiwalik range. The mountainous areas of Shiwalik range has forest or mountain soil. The soil here is the result of deposition of sediments brought by Gandak, Burhi Gandak,Mahananda, Kosi and Saryu rivers.
North plain soils can be classified into four types. i. Piedmont Swamp Soil ii. Terai Soil iii. Alluvium Soil iv. Domat Soil
i. Terai Soil
➤ This type of soil is found in Northern part in a narrow belt along the border of Nepal to the South of Someshwar range and from West Champaran to Kishanganj and Araria districts.
➤ This soil is heavy in texture in the Western part while the soil of the South-East region has high texture due to the influence of the Kosi and Mahananda rivers.
➤ This soil is grey to yellow in colour which is not well drained and neutral to moderately acidic in reaction. It is rich in lime and has small gravels.
➤ It has a medium order of fertility. The lowland Terai soil is more fertile compared to upland Terai soil.
➤ In the lowland Bhadai and Aghani crops like rice, sugarcane, jute, maize, vegetables and oilseeds are grown while the uplands remain mostly barren with growth of mainly millet, marua, kulthi, sweet potato, arhar, etc.
ii. Piedmont Swamp Soil
➤ This soil is found in North-Western part of West Champaran district. This soil is shallow to deep and has rocks and pebbles.
➤ This soil is mostly clayey, rich in organic matter and neutral in reaction. This supports good rice crop, maize and barley crops.
➤ Marshy land has been developed in this soil at some places due to excessive rain and moisture. It is light brown or yellow in colour and acidic in nature due to the predominance of forests.
iii. Alluvium Soil
➤ This soil lies South of the Terai Soil belt. This is a broad belt which tapers towards North-West and broadens in the South-East.
➤ This soil is thicker towards North and thinner towards South and has medium productivity.
➤ Important crops grown in this soil are jute, paddy, wheat, maize, pulses like gram, masur, khesari and oilseeds like mustard, etc.
➤ The soil is deficient in phosphorus and nitrogen due to which it resembles as brown and white in colour.
The soil is further divided into two types, such as:
New Alluvium or Khadar Soil
➤ This is a newer alluvium soil which is found in lowlands and in the vicinity of rivers where fresh deposits renew it periodically.
➤ It is sandy in the upper reaches while silty in the lower section. The soil is less calcareous and carbonatic than Bhangar soil and has less kankar concentration.
➤ Surface of Khadar soil is levelled due to periodic deposition of silt. Khadar soil is suitable for crops like wheat, paddy, etc.
➤ Due to having better drainage except in river beds, it has low percentage of humus and nitrogen and little lime, thus is more suitable for many crops.
➤ It is dark brown in colour. It is extended in Ganga valley and lower valleys of Gandak, Burhi Gandak, Kosi and Mahananda rivers.
➤ It is mainly found in flood prone regions and is extensively found in Purnia and Saharsa districts. Jute is also grown in this soil in the North-Eastern parts of Bihar due to having higher rainfall.
Old Alluvium or Bhangar Soil
➤ This is an older Alluvial soil which is found in Western parts of Ghaghara-Gandak Doab and Burhi Gandak. It is mostly loamy with high clay factor.
➤ Its drainage is poor due to high clay concentration. This makes the soil sticky.
➤ Kankar or carbonaceous compounds are abundant in this soil.
➤ The difficulty in its tillage makes it suitable for paddy cultivation. It is rich in lime (more than 30%) and potash which makes it suitable for sugarcane cultivation.
➤ This soil is under the process of denudation. The sub-soil has an impervious clay layer.
Bhangar has two varieties of soils such as :
— Balsundari Soil It is found from the Southern part of Purnea to Saharsa, Darbhanga, Muzaffarpur, Siwan, Saran and Gopalganj district. It is rich in lime which is suitable for fruits like mango, banana and litchi, and crops like paddy, sugarcane, wheat, maize, tobacco, etc.
— Bhat Soil The Central-Western North Bihar plains in the lower Gandak valley have Bhat or calcareous soil. It is a chemical variant of the alluvial soil.
iv. Domat Soil
➤ It is found in a broad belt in the South-western portion of the North-Bihar plain.
➤ The Eastern region is dominated by young calcareous alluvial soils while Western part especially Siwan and Saran districts have young calcareous alluvial soil with saline and alkali soil.
➤ The Eastern domat soil is white to olive grey in colour but appears dark grey in the vast lowlying area of this region which are known as ‘Chaurs’. This soil has medium to high fertility.
➤ Important crops which are grown in this soil are maize, paddy, wheat, sugarcane, tobacco, etc. Mango and litchi are also grown here especially in Muzaffarpur and Vaishali districts and Banana is majorly grown in Vaishali district, especially around Hajipur city.
