Problem hydromorphic soils in north-east Thailand. 2. Physical and chemical aspects, mineralogy and genesis.

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Abstract
The Roi Et soil, which occurs on the extensive seasonally wet low terrace, is a silt loam with low clay contents in the surface horizon; the clay content increases with depth. The soil is seasonally water-saturated and seasonally dry, has considerable porosity, but has a dense ploughpan at a depth of about 0.2 m and a dense substratum below 1.4 m. The soil is strongly acid with a low base saturation and a very low cation exchange capacity. The silt and sand are 98% quartz. Disordered kaolinite is the main clay mineral. About a fifth of the clay fraction is soil chlorite - a strongly Al-interlayered vermiculite in the upper horizons but partially Al-interlayered in the substratum. The interlayers contain a small amount of ferrous iron. The quartz contents in the clay fractions range from one tenth in most of the profile to about three tenths in the surface horizon, with a corresponding decrease in kaolinite. The kaolinite in the upper horizons shows signs of dissolution. These data are in accordance with hypothetical clay eluviation-illuviation and long-continued Fe redistribution and ferrolysis, the ferrolysis involving clay alteration and dissolution under conditions of alternating reduction and oxidation of Fe. (Abstract retrieved from CAB Abstracts by CABI’s permission)

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