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

Next to kaolinite, the aluminum hydroxide gibbsite, is moderately abundant in the Nyangong
and Ebom soils. Gibbsite forms in richer parent material (Driessen and Dudal, 1989; 1989; Mohr et
al., 1972; van Kekem et al., 1997). The drainage conditions of the Ebimimbang soils, are less
good when compared to the two other soil types. This might be the explanation for the
difference in gibbsite contents of the different soil types.
Vermiculite, chlorite and smectite are clay minerals which are absent or only present in
relatively small amounts in the TCP research area. area. Micas (illite) are moderately abundant in
some soil samples, but no relation relation is found with the different soil types. Feldspars and quartz
are absent or only present in small amounts the clay fractions.
The iron hydroxide goethite is moderately abundant in all soils, whereas whereas the iron oxide hematite
is absent in the three main soil types of the TCP area. Goethite is formed under a soil climate
with sufficient moisture in the dry season season even if the soils are well drained. It gives the soil a
yellowish brown colour (Bilong, 1992). Driessen and Dudal (1989) (1989) state that goethite is formed
when the iron concentration is low, the organic matter content is high, the temperature is low
and/or soil pH is lower than 4.0.
5.4.6 Nutrient contents
Combining bulk density data data and chemical chemical data makes it possible to calculate the total total amounts
of nutrients potentially available for plant growth. The data give an indication of the fertility of
the different soils. The calculated nutrient contents for the three main soil types are averages of
four four to six profiles. Table 5.5. 5.5. shows the the nutrient contents contents in kg/ha for a soil column of 1 meter
deep. The majority of these nutrients, however, are concentrated concentrated in the upper 20 cm of the soil
profile. profile.
The Nyangong soil has a relatively high nitrogen content (12.5 ton/ha), whereas whereas available
phosphorous and potassium are present in relatively relatively small amounts of 8 and 360 kg respectively
(Table 5.5.). Magnesium and calcium amounts are 195 and 1065 kg/ha, respectively. The Ebom
soil has less less total nitrogen (8900 (8900 kg/ha), but a moderate amount of phosphorous (28 kg/ha). The
Ebimimbang soil also has a moderate amount of available phosphorous (24 (24 kg/ha) but the total
nitrogen nitrogen amount is low (7000 kg/ha). The potentially available K, Mg and Ca amounts are in the
same order of magnitude for all three soils.
Table 5.5 5.5 Average nutrient contents of the Nyangong, Ebom and Ebimimbang soils in kg/ha kg/ha
(soil column of of 1m)
Soil type Total Total N Available P K Mg Ca
Nyangong soil (n=6) 12500 8 8 360 195 1065
(7371-24338) (3-16) (168-805) (168-805) (86-336) (607-1876)
Ebom soil soil (n=4) 8900 8900 28 755 175 1785
(5616-13022) (5-59) (361-1601) (60-306) (867-3558)
Ebimimbang soil soil (n=6) 7000 24 370 165 165 1810
( 4963-8757) (11-42) (11-42) (176-395) (27-535) ( (1295-2088) 1295-2088)
The nutrient nutrient contents of the soils in the TCP research area area are comparable with data data from other
studies on on humid tropical forest soils (Anderson and Spencer, 1991; Gillman et al., 1985).
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