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

The present study confirms that deep, moderately well to well drained yellowish brown brown tropical
clay soils predominate in the TCP research area. These soils also described as 'les sols
ferrallitiques jaunes sur les roches acides (gneiss)' are characterized by Martin and Segalen (1966)
as follows:
topsoil (3-10 cm): 15 to 20% clay, ± 3.5% organic matter (CIN = 15), CEC < 8 meqllOO g, base
saturation between 12 and 20% and pH < 4.5;
subsoil (> 10 cm): 35-50% clay, low in organic matter « 3.5%), CEC between 5 and 7 meq/l00
g and base saturation < 10%.
Vertical clay movement is described. The mineralogical composition of the clay is: 50-60%
kaolinite, 35-45% goethite and < 10% gibbsite and the Si02/Al203 ratio is between 1.1 and 1.6.
5.2 SOIL TYPES AND CLASSIFICATION
The soils in the Bipindi - Lolodorf - Akom II area have been subdivided into four main soil types.
This subdivision is based on soil drainage and texture in both topsoil and subsoil (table 5.1).
Well drained, deep deep to very deep deep1, 1, yellowish brown to strong brown clay clay soils, classified according
to FAO-Unesco (1990) as Xanthic Ferralsols, are dominant in the area. These well drained soils
are further subdivided according to the clay content in topsoil and subsoil into:
Nyangong soils which which are very clayey soils soils with no or only a a gradual increase in in clay content
with depth. The clay contents contents of ofthe the subsoils range between 50 and 80%.
- Ebom soils which are clay soils with a gradual to strong differentiation in clay content between
topsoils and subsoils. subsoils. The clay clay contents of the subsoils range between 35 and 60%.
The moderately well drained soils are:
Ebimimbang soils which are moderately deep to very deep clay soils with sandy topsoils. The
clay contents of the subsoils range between 20 and 45%.
The poorly to very poorly drained soils are:
- Valley Bottom soils soils which which are moderately deep to very very deep soils, locally stratified and with
variable textures in topsoils and subsoils.
The first three soil types are named after villages in the TCP area in which regions these
corresponding soil types dominate. The Valley Bottom soils are, as the name implies, restricted
to the valleys and occur all over the area.
Soil depth, soil stoniness stoniness and and the occurrence occurrence of plinthite in the subsoils subsoils are are other criteria for further further
subdivision of the soils. During the present reconnaissance survey it has, however, not been
possible to find systematic relationships between these factors and positions in the landscape.
Therefore, these criteria have not been used to further subdivide the four main soil types mentioned
above.
Soil depths classes are as follows: shallow 0-50 cm; moderately deep 50-100 cm; deep 100-150 cm cm and very very deep
>150 >150 cm.
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