Clay Illuviation and Pedoturbation in SAT Vertisols

Abstract

For a long time the apparent uniform distribution of clay throughout Vertisols was considered to be effect of haploidisation within the pedon caused by pedoturbation and in some cases the observed gradual increase in clay content with depth was thought to be due to inheritance from parent material. Recent systematic pedological studies on Vertisols that have no stratification in the parent material and no clay skins, indicated that their Bss horizons contain clay even up to 20%; an increase from the eluvial horizon. Such depth distribution of clay is due to clay illuviation process was confirmed by micro-morphological investigation of the thin sections, which indicated the presence of >2% impure clay pedofeatures. Thus the clay enriched Bss horizons in Vertisols suggests that pedoturbation was too much favoured as an important pedogenic process in Vertisols by the past researchers till early nineties, who envisaged pedoturbation would obliterate all evidence of illuviation. But in reality, pedoturbation in Vertisols is only a partially functional process, which cannot overshadow the more significant long-term clay illuviation process. Although the micro-morphological study of soil thin sections is a unique analytical tool to confirm clay illuviation process, for many of the national soil science laboratories it is truly a very distant facility. In its absence some simple analytical data are of much help in ensuring the clay illuviation process with certainty as major pedogenic process in Indian Vertisols, which are described in this chapter.