Abstract
AbstractFourteen soil profiles from southwestern Indiana were studied to determine the effects of loess thickness and natural soil drainage on the profile distribution of clay and free oxides (CBD‐extractable) of Fe, Al, Mn, and Si. In all soils, Fe and Al curves follow the clay curve, suggesting that the oxides are adsorbed on clays and move with them. Natural soil drainage had little effect on profile distribution of clay, Si or Fe. Free Al2O3 contents increase slightly with poorer drainage. With thinning loess, clay and free Fe2O3 distribution changes little, free Al2O3 contents increase slightly, free MnO2 curves have more pronounced minima and maxima, and free SiO2 increases significantly in fragipan horizons. We propose that free silica moves down the profile in solution and precipitates, possibly with aluminum hydrous oxides on clays. The resulting silica or alumino silicate binds particles together to form the hard, brittle soil material of fragipans.
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