Influence of Moisture Regime on the Genesis of Laterite Soils in South India II. Clay composition and mineralogy

The chemical composition of the clay fractions indicates reduction in SiO₂ and increase in Fe₂O₃ and Al₂O₃ with increase in rainfall in a similar manner to that of soils as reported in earlier communication. The clay minerals present are dominated by kaolinite under ell moisture regimes. Quartz is also noted in small qnantities in all clay fractions irrespective of the climatic conditions. Gibbsite occurs both in high and excessive rainfall groups of absent in low rainfall group. Laterization process, as judged by the visual intensity of gibbsite indicated by D. T. A. and X-ray diffraction patterns, is found to be enhanced with high and excessive rains concentrated in seven months having K index above one. With high rains a distributed over a pert Jd of nine months, tlie laterization process is found to be retarded. Dry spell of about five months (K index below one) appears to be essential for laterization. Excessive rains seem to be ineffective in further enhancement of laterization process.