Soils of Bihar
■ Bihar is primarily an agricultural state and almost all the economic activities are directly or indirectly dependent on soil.
The soil covering most of Bihar is thick alluvium which shrouds the Siwalik and older tertiary rocks. The soil is mostly fresh loam replaced every year by intermittent deposition of silt, clay and sand by different rivers. It lacks phosphoric acid, nitrogen and humus but potash and lime are generally present in large amounts.
There are three major types of soil in Bihar:
- Piedmont Swamp Soil
- Terai Soil
- The Gangetic Alluvium
■ Piedmont Swamp soil:
The word piedmont is derived from two Italian words 'pied' meaning foot and 'monte' meaning mountain. In geology, piedmont is defined as a landform created at the foot of a mountain or mountain range or say, area at the bottom of a mountain or mountain range. Such an alluvial region/zone in the humid climate is known as the Piedmont area or Piedmont zone.
Swamp refers to a seasonally flooded bottomland with more woody plants than a marsh and better drainage than a bog. Simply, it's a lowland region saturated with water.
Piedmont swamp soil is found in the area immediately below foothills which are sloping and largely composed of gravels and sand, with interspersed boulders brought down by floods produced by torrential rains. These areas are also known as Bhabar Plains or Upper Piedmont Zone.
They are occasionally with sand and clay beds. Composition to these soils, their porosity, and their inability to retain water are some factor that makes them unfit for cultivation.
In Bihar, this type of soil is found in the northwestern part of West Champaran district.
■ Terai Soil:
The area below the Bhabar is merged with the alluvial plains composed of finer materials called Terai Plains. The underground streams of the Bhabar belt re-emerge in this belt.
The soil in the Tarai is composed of coarse-grained sand and clays with gravel. It is alluvial and fine to medium textured. Terai Soils are rich in nitrogen and organic matter but deficient in phosphate. This soil is suitable for Paddy, Sugarcane and Jute cultivation.
In Bihar, this type of soil is found in the northern part of the state along the border of Nepal.
■ The Gangetic Alluvium:
In the Indo- Gangetic plain the Alluvial soils are derived from the sediments deposited by rivers. Thus the parent material of these soils is all of transported origin. The alluvial soils are immature and have weak profiles. They differ in consistency from drift sand to rich loams and from silts to stiff clays.
The proportion of nitrogen is generally low, but potash, phosphoric acid and alkalies are adequate, while iron oxide and lime vary within a wide range. The porosity and texture provide good drainage and other conditions make it most favourable for agriculture.
Geologically, the alluvium of the Great plain of India is divided into newer or younger Khadar and older Bhangar soils.
Khadar
- It is composed of newer alluvium and forms the flood plains along the river banks.
- The banks are flooded almost every year and a new layer of alluvium is deposited with every flood. This makes them the most fertile soils of Ganges.
- The soils are generally grey to ash grey or pale brown in colour and its texture varies mostly from clayey to sandy loam.
- It is generally highly leached and is low in humus and nitrogen and poor in lime.
- It is less calcareous and carbonaceous i.e. less kankary (कांकरी).
- It corresponds to the Recent Period.
- This soil is suitable for Wheat, Paddy, Maize, Gram, Sugarcane etc.
Bhangar
- It is the older alluvium along the river beds forming terraces higher than the flood plain (about 30 metres above the flood level).
- It is of a more clayey composition and is generally dark-coloured.
- A few metres below the terrace of the Bhangar are beds of lime nodules known as “Kankar”.
- It corresponds to the mid-Pleistocene period.
- This soil is more suitable for paddy while other crops include Jute, Sugarcane, Arhar (pigeon peas) etc.
Alluvial soil is mainly found in almost the entire plains of Bihar, except the sub-Himalayan hills and forest soils which is mostly found in the northern parts of West Champaran district. It covers the entire landmass of the north of the Ganges. There is a considerable area to the south of the Ganges with alluvial deposits in the districts of Bhagalpur, Munger, Patna, Nalanda, Gaya, Aurangabad, Nawada, Rohtas and Bhojpur.
Calcareous alluvial soil: It contains a high content of carbonate of lime and is found in a vast patch in the portion of Bihar plain covering parts of Saran, Champaran, Muzaffarpur, Darbhanga and Saharsa districts.
This soil is suitable for litchi plants.
Other soil types in Bihar:
■ Sandy soil: This type of soil is locally known as 'Baluahi' and is found near the banks of the river.
■ Kewal Soil: This type of soil is a mixture of clay and loam and is very productive with high water retention capacity. This soil is suitable for Rabi crops like Wheat, Gram, Peas and Barley etc as these crops depend on sub-soil moisture to a great extent.
One variety of Kewal in the Barh subdivision is known as Tal soil. This remains submerged during the rains and is suitable for growing rice but the main produce is Rabi crop.
It is light to dark grey in colour with texture ranges from medium to heavy and pH varies between 7 and 8.
■ Peaty soils: These are found in the area of heavy rainfall and high humidity, where there is good growth of vegetation resulting in the accumulation of dead Organic Matters (OM) in large quantities which gives rich humus and organic content to the soil. OM in these soils goes even up to 40-50 per cent.
It occurs widely in the northern part of Bihar.
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