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

The Valley Bottom soils have organic carbon contents contents of 2.5-6.5% 2.5-6.5% in the topsoils. The total
nitrogen contents of the topsoil are comparable with the other soils. The subsurface horizons
show organic carbon and total nitrogen contents similar to those of the Ebom and Ebimimbang
soils.
5.4.3 Available and total phosphorous
The available phosphorous content in the topsoils of the Nyangong soils ranges between 4 and
11 ppm (low), in the Ebom and Ebimimbang soils between 10 and 26 ppm (moderate) and in the
Valley Bottom soils between 30 and 60 ppm (moderate to high). With depth, available
phosphorous contents drop rapidly to values below 5 ppm and are invariably approaching 0 in
all subsoils.
Total phosphorous contents of the topsoils are high in the Nyangong soils and range between
400 and 600 ppm. With depth, these values go down to 50-250 ppm. The Ebom and Ebimimbang
soils have 150-400 ppm total phosphorous in the topsoils and 50-250 ppm in their subsoils. Total
phosphorous contents of the Valley Bottom soils are not available.
Higher available phosphorous contents coincide with higher pH values as at higher pH values
phosphorous is less fixed in aluminium and iron complexes than at lower pH ranges. The higher
available phosphorous contents of the Valley Bottoms are explained by colluvial enrichment.
Table 5.4b 5.4b Ranges in some chemical chemical characteristics of the four soil types types in the TCP TCP research
area
Soil type Depth Depth K+ Mg++ Ca++ TEB Al+++ Al+++ ECEC ECEC CEC CEC BS
(%)
Nyangong 1 0.1-0.5 0.2-0.8 1-2 1.5-3.5 4-9 6-10 10-20 10-20
2 0-0.1 0-0.5 0.2-0.6 0.5-1.2 2-6 5-7 6-9 5-15
Ebom 1 0.1-0.9 0.4-1.6 0.5-4 2-5 0.5-6 4-9 12-25 10-50
2 0-0.2 0-0.5 0-0.5 0.3-1 2-5 3-6 5-8 5-20
Ebimimbang 1 0.1-0.7 0-1.5 1-8 3-7 0-3 3-10 4-12 50-100
2 0-0.2 0-0.5 0-2 0.2-1.5 1-2.5 1.5-1 2-6 10-70
Valley 0-0.5 0.3-1.5 0.5-4 4.5-6 0-3 5-7.5 7-17 15-50
Bottom 2 0-0.1 0-0.2 0-0.5 0.5-0.8 0-1.5 0.5-2 1-8 20-40
Soil depth: 1 = topsoil, generally 0-10 cm; 2 = subsurface horizon of about 20-60 cm depth. TEB = Total
Exchangeable Bases. ECEC = Effective Cation Exchange Capacity. CEC = Cation Exchange Capacity. BS = Base
Saturation. All values, except BS, in meq per 100 g.
5.4.4 Cation exchange capacity and exchangeable bases
The cation exchange capacities (CEC) of the topsoils in the study area are low to moderate with
CEC values of 4-20 mellOO gr soil. With depth the CECs drop rapidly to low levels of 1 to 9
me/lOO gr in the subsurface horizons to even lower levels in the subsoils. The relatively higher
CEC values occur in the topsoils topsoils of the Nyangong Nyangong and Ebom soils and are between between 10 and 25
mell me/lOO 00 g soil. These higher values are directly related to the higher organic matter levels of
these soils.
The exchange exchange complex complex is dominated dominated by aluminium aluminium (AI) and Al saturation saturation percentages percentages of 30 to
80% are common. The highest saturation values occur in the soils with the lowest pH values,
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