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Abstract

Large areas in the plains of Indus and Ganges rivers are sodic in nature. In these plains alkali soils occur in patches along with normal (non-alkali) soils in the immediate vicinity.  In spite of alkali soils having very poor water transmission characteristics, clay skins are present in both alkali and adjoining normal soils. In alkali soils A horizon has lower clay content than B horizon. However, clay content of the B horizon of alkali as well as adjoining normal soil is almost identical. In order to determine the genesis of clay skins and apparent higher clay content in B horizon, three alkali soils and one adjoining non alkali soil were investigated. Uniformity of parent material of alkali and adjoining normal soils has been indicated through mineral assemblage studies using XRD.  Increase in K2O content of sand and silt fraction with depth indicated lack of in-situ clay formation in B horizon.  Absence of decreasing SiO2 to R2O3 ratio in clay fraction of alkali soils and non alkali soil, and lack of total clay to fine clay ratio maxima in the B horizon of alkali soil suggest absence of clay migration in these soils. Occurrence of large number of argillans, and infillings of pure clay in both A and B horizons of these soils suggest the origin of such coatings to be a process other than leaching of clay. Micromorphological investigation indicating presence of pure clay argillans and clay fillings support erosion in A horizon leading to loss of clay.  Large scale fluctuations in ground water table, together with ustic soil moisture-regime resulted in deposition of dispersed clay locally on the peds of both alkali as well as normal soils of this region.

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