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

Table 5.3 Soil physical physical characteristics of the Nyangong, Nyangong, Ebom and Ebimimbang soils
Soil type type Depth Texture Texture Texture Texture Bulk Bulk density AWe
(clay%) (silt%) (silt%) (sand%) (g/cm3) (%)
Nyangong I 35-70 10-20 10-40 1.03 10
2 50-80 50-80 5-15 10-40 1.21 12
3 1.26 7
Ebom I 20-50 5-20 40-60 1.22 17
2 35-60 35-60 5-15 30-50 1.37 16
3 1.4 1.4 12
Ebimimbang I 0-25 5-15 60-90 1.3 11
2 20-45 5-15 40-80 1.55 15 15
3 1.63 n.a.
Soil depth classes: I = 0-20cm; 2 = 20-60 cm; 3 = 60-90cm. Bulk density values are the average of at least 4
observations. A AWC= WC= Available Water Content (one or two observations per soil depth class).
The Valley Bottom soils are dominated by a sandy texture, but in fact all all texture texture classes classes may may
occur in in all possible possible sequences. Stratification is characteristic for these soils. In general, general, the
Valley Valley Bottom soils have have 5-30% clay and 40-90% sand sand in the topsoil. The subsurface horizons
generally are more sandy.
5.3.2 Bulk density
The ranges ranges in bulk bulk densities densities of of the the soils soils in the TCP research research area area are 0.8 to lA g/cm3 in in the
topsoils topsoils (0-10 cm) and 1.0 to 1.7 g/cm g/cm 3 in the subsoils (20-90 cm) (Table 5.3). The bulk
densities of all three three main soil soil types increase strongly with depth, depth, as as effects effects of cultivation cultivation and and
organic matter matter content decrease. decrease. The The increase of of the bulk densities with depth take place 'within
25 25 cm from from the the surface. The The bulk densities of of the Nyangong/Ebom soils and the Ebimimbang
soils are within the normal range of 1.0 to 1.6 g/cm g/cm3 3 and 1.2 to 1.8 g/cm g/cm 3 as given by Landon
(1991) for clayey and sandy soils, respectively.
3 as given by Landon
(1991) for clayey and sandy soils, respectively.
Average values of bulk densities for the Nyangong, Ebom and Ebimimbang soils at three depths
(0-20 cm, 20-60 cm and 60-90cm) are given in Table 5.3. The Nyangong topsoils have bulk
densities of around 1.0 g/cm3, and below 20 cm the bulk densities increase to values of 1.2 to
1.3 g/cm3. The topsoils and subsurface horizons of the Ebom soils have bulk densities around
1.2 and lA g/cm3 Average values of bulk densities for the Nyangong, Ebom and Ebimimbang soils at three depths
(0-20 cm, 20-60 cm and 60-90cm) are given in Table 5.3. The Nyangong topsoils have bulk
densities of around 1.0 g/cm3, and below 20 cm the bulk densities increase to values of 1.2 to
1.3 g/cm
, respectively. Bulk densities of the Ebimimbang soils are the highest of the
TCP research area, i.e. 1.3 g/cm 3 for the topsoils and 1.5 to 1.7 g/cm 3 for the subsoils. There is
thus an increasing bulk density with a decreasing clay content.
3 • The topsoils and subsurface horizons of the Ebom soils have bulk densities around
1.2 and 1.4 g/cm3 , respectively. Bulk densities of the Ebimimbang soils are the highest of the
TCP research area, i.e. 1.3 g/cm3 for the topsoils and 1.5 to 1.7 g/cm3 for the subsoils. There is
thus an increasing bulk density with a decreasing clay content.
The Ebimimbang soils have less stable aggregates than the Ebom and Nyangong soils (Waterloo
et al., 1997), resulting in vertical clay movement and lower permeability of the Ebimimbang
soils. The higher bulk densities of the Ebimimbang Ebimimbang soils are explained by the lower aggregate
stability and higher sand sand contents of these soils.
Topsoils under agriculture have decreased organic matter contents and less roots resulting in
higher bulk densities densities compared to identical soils soils under forest (pers. comm. comm. Yemefack, 1996). 1996).
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