[en] Landscape Ecological Survey of the Bipindi-Akom II ... - ITTO

Clay eluviationlilluviation is the redistribution of clay in the profile, resulting in an increase in
clay content with depth. Mobilized clay is transported downward and deeper in the profile where
it is immobilized (Driessen and Dudal, 1989). Cutans of clay on the structural elements in the
subsoil subsoil are evidence for recent illuviation. Biological activity may destruct these clay cutans. cutans.
These cutans are mainly found in the Ebimimbang soils in the western lowlands in the TCP
research area (40-350 m as!). All soils in the TCP research area have a clay increase with depth,
but cutans are rarely found in the eastern part. Clay movement is probably related to the past
when the soil was still less weathered and soil pH was somewhat higher than at present (van
Kekem et al., 1997).
In the oxidation phase, the presence of oxygen leads to the transformation of soluble ferrous
compounds to ferric compounds. These precipitate on soil particles, giving the soil its reddish
colour. The reverse occurs during the the reduction phase. The lack of oxygen oxygen causes causes dissolution
of ferric compounds, giving the soil the colour colour of non-ferrous minerals, forming its matrix (grey, (grey,
olive or blue matrix matrix colours). This soil soil forming process of oxidation-reduction is associated with
the fluctuation of the groundwater table. In the zone with alternating oxidizing and reducing
conditions, mottles are often formed (Driessen and Dudal, 1989). This soil forming process is
important in the Valley Bottom soils.
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