Sodiumization of Some Alfisols in Toposequence Occurring in IndoGangetic Plain of Bihar

Sodiumization in two identical toposequences occurring in some Alfisols of the Indo-Gangetic plain in Bhagalpur district of Bihar is observed. Labradorite is the chief mineral source for the sodicity. The soils are almost identical in nature due to hydrological variability as influenced by depth of water table in differing landforms under sub-tropical situation. The formation of soils is both geologic and pedogenic in nature. They contain appreciable amount of MgO. The saturation extract of soils indicates high sodium content while anions are present in the order: HCO_3⁻ > SO_4^2- > Cl⁻. The ground water contains appreciable amount of Na⁺ ion and anions are in the order: sot > HCO_4^2- > Cl. High rainfall in a topographic position could have accentuated the process of sodiumization under differential wet-dry sequences.