Chemistry of pedogenesis in Indo‐Gangetic alluvial plains

Abstract

SUMMARYFive soil pedons–two aquic and two udic Haplustalfs and one petrocalcic Natrustalf–from the Indo‐Gangetic alluvial plain of Western Uttar Pradesh were investigated to evaluate the pedogenetic processes. Sand/silt ratios indicate that parent material discontinuities are insignificant. Higher K content and lower SiO2/R2O3 ratios of the non‐clay fractions in Bt, rather than in the A, horizons suggest maximum weathering at or near the surface.An almost linear relationship between decrease in molar SiO2/R2O3 and % increase in clay to about 100cm depth in all the pedons, presence of clay argillans in Bt horizons (where % clay, fine/coarse clay ratio and bulk density values are greatest), all indicate that the development of argillic horizons in these soils was due, at least partly, to lessivage of clay. Fe in clay fractions decreases with depth whilst Al increases, but in the fine earth both increase steadily with depth. This, together with crystalline iron concretions in the lower Bt horizons, suggests that in Haplustalfs these horizons are gaining clay by neoformation/ reorganization of illuviated constituents, especially A12O3.