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

Table 5.1 Soil types of the TCP research area and their diagnostic criteria
Soil type
Drainage
Nyangong
Well drained
Ebom
Well drained
Ebimimbang Moderately well drained
Valley Bottom Poorly to very poorly drained
Topsoil Topsoil = 0-10 0-10 cm; cm; subsoil subsoil = 20-60 20-60 cm cm
Texture
(% clay topsoil)
35-70%, very clayey
20-50%, clayey
0-25%, sandy
variable
Texture
(% clay subsoil)
50-80% 50-80%
35-60%
20-45%
variable variable
5.2.1 Nyangong soils
The Nyangong soils are deep to very deep, well drained, yellowish brown to strong brown, clays
with dark yellowish brown to dark brown clay topsoils. They are developed on fine grained,
pyroxene rich gneisses and granites, or other igneous rocks. Soil depth of the deep soils (100 -
150cm) is limited by the occurrence of ferruginated gravel, stones, boulders or weathering
bedrock. Nyangong soils are characterised by a high clay content which can reach 80% in the
subsoils. The topsoils are none to slightly less clayey than the subsoils whereby the increase in
clay content with depth is gradual.
The topsoils are 10 to 20 cm thick with the first 5 to 10 cm having the darkest colours. They
have dark yellowish brown to dark brown colours and 40 to 70% clay. The subsoils have
yellowish brown to strong brown colours and clay contents of 50 to 80%. In places few reddish
mottles and/or laterite gravel is found in the deeper subsoils.
Locally on summits, upper slopes or very steep mountain slopes, moderately deep to very deep,
gravelly and stony soils occur as inclusions within the Nyangong soils. These have clay contents
in the subsoils of 40 to 50% and are less deeply and less intensively weathered than the typical
Nyangong soils. At the present scale of the survey, these soils could not be mapped separately.
The Nyangong soils are characteristic for altitudes above 500 m asl and are therefore found in
the mountains and hills in the eastern part of the TCP area. The complexes of hills and isolated
hills at altitudes above 500 m are also mainly covered with the Nyangong soils. The soils of the
eastern uplands form complexes ofNyangong and Ebom soils.
Full profile descriptions with analytical data of the Nyangong soils are given in Annex IV.
5.2.2 Ebom soils
The Ebom soils are deep to very deep, well drained brownish yellow to strong brown, clays with
yellowish brown to dark brown sandy loam to sandy clay topsoils. They are developed on
gneisses and migmatites. Soil depth of the deep soils (100-150 cm) is limited by plinthite,
laterite and/or quartz gravel or bedrock. A relationship between the occurrence of plinthite or
limited soil depth within 150 cm and topographical position, could not be detected and therefore
not mapped at the scale on the survey. The Ebom soils are characterized by their clayey subsoils
with less clayey topsoils whereby an increase in clay content with depth of about 10% generally
occurs within 20 to 25 cm of the surface.
The topsoils are 10 to 20 cm thick, have yellowish brown to dark brown colours (with the first
5 cm having the darkest colours), and have 20 to 40% clay (sandy loam to sandy clay). The
subsoils generally have 40 to 50% clay with an observed range of35 to 60% and have brownish
yellow to strong brown colours, with yellowish brown dominating. In a majority of the soils
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