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BIHAR

Geographical position and climate

Bihar state is located between 24°17' and 27°31'30''N latitude and longitudes of 83°19' and
88°17'E with an average length of 483 km to the east-west and average width of 385 km to the
north-south.Based on rainfall, temperature, terrain and soil characteristics, Bihar state has been
broadly delineated into three agro-climatic zones. Zone I – North West Alluvial Plains zone
comprises, west and east Champaran, Gopalganj, Siwan, Saran, Sitamarhi, Muzaffarpur,
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Vaishali, Madhubani, Darbhanga and Samastipur with an area of 32665km . Zone II – North
East Alluvial Plain zone comprises, Purnea, Katihar, Saharsa and Begusarai districts. Zone III –
South Bihar Alluvial Plains zone is located in the south of river Ganga and comprise of Gaya,
Aurangabad, Rohtash, Bhojpur, Patna, Nalanda, Munger and Bhagalpur. The total geographical
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area of this zone is 44875.5 km .
The climate is characterized by tropical to subtropicalclimate, humid to sub humid
monsoon type. The mean annual rainfall varies from 2000 mm near the northern and north
eastern corner of state to a minimum of 1000 mm on the western border along the Ganga axis.
The mean annual temperature varies from 24 to 26°C with mean summer temperature ranging
between 28 and 33 °C and mean winter temperatures between 17 and 19 °C. Central portion of
Purnea district is warmer in June and very cold in January as compared to Madhepura and
Saharsa, where maximum and minimum temperatures are 40 °C and 8.3 °C, respectively.

Soils
The soil are grouped as sub-Himalayan and forest soils, recent alluvial tarai soils, young alluvial
calcareous soils, calcareous saline soils, non-calcareous non saline soils, and recent alluvial
calcareous soils.The upland soils are well drained to moderately well drain. The medium low
lands and the low land soils although of good moderate permeability, have become somewhat
poorly drained due to high water table in the areas. In North East Alluvial Plain zone, the soils
are very light to medium textured except for those in between the natural levees of Ganga and
Kosi and Mahananda and away from the influence of running water of rivers. Even the heavy
textured soils under the influence of Kosi and Mahananda have sandy substratum below 40 to
100 cm depths. The soils are mostly moderately acidic to neutral. Very acidic soils are found in
northeast parts with heavy rainfall and high permeability. The soils are moderately rich to poor in
nitrogen (especially in Gopalganj and Siwan districts), moderated to very low in available
phosphorous and medium to high in available potash. Soils are deficient in zinc and iron mostly
induced by high available calcium.
In south Bihar alluvial plains zone, the soils of this zone are moderately well drained to
somewhat poorly drained, moderately acidic to slightly alkaline and medium textured to heavy
texture soils. The Diara land soils with their undulating landscapes are generally very light to
medium heavy textured but all underlain by sandy layers within 80 to 100 cm of their surface
and very well drained to moderately well drained, neutral to slightly alkaline in reaction. Their
fertility status varies widely from poor to very fertile depending upon their physiographic
positions but all are under moisture stress due to the occurrence of sandy substratum.