Agriculture Reference
In-Depth Information
deforestation. On the plateau, elements released by surface degradation are transported
deep into the profile. Al is concentrated as kaolinite and gibbsite and Si is
leached. On slopes, lateral water flow is more intense and greater amounts of Al are
leached resulting in a relative concentration of as quartz sand. Podzolisation occurs
in these sandy areas, starting from low-lying areas and progressing upslope as the
slope develops. This transformation is related to percolating water and starts at the
plateau edges from where it progresses towards the centre, further contributing to slope
development. In French Guiana, contrasting systems occur in which podzolisation
progresses from the centre to the edges. In the latter case, podzolisation is initiated by
the formation of a perched water table following clay eluviation and deposition lower
in the profile (Boulet
et al.,
1984). The properties of very old soils (palaeosols) are
discussed in Section II.4.4.3.
Local differences in parent materials (Section II.2.2), drainage, topography and
the biota may lead to large differences between soils over short distances. Pedogenetic
processes may be conditioned by the characteristics of the original parent material.
As discussed earlier in this chapter, clear differences may result between soils formed
on different parent materials although these diminish with soil age (Chesworth, 1973a).
