[en] Landscape Ecological Survey of the Bipindi-Akom II ... - ITTO
[en] Landscape Ecological Survey of the Bipindi-Akom II ... - ITTO
[en] Landscape Ecological Survey of the Bipindi-Akom II ... - ITTO
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Next to kaolinite, <strong>the</strong> aluminum hydroxide gibbsite, is moderately abundant in <strong>the</strong> Nyangong<br />
and Ebom soils. Gibbsite forms in richer par<strong>en</strong>t material (Driess<strong>en</strong> and Dudal, 1989; 1989; Mohr et<br />
al., 1972; van Kekem et al., 1997). The drainage conditions <strong>of</strong> <strong>the</strong> Ebimimbang soils, are less<br />
good wh<strong>en</strong> compared to <strong>the</strong> two o<strong>the</strong>r soil types. This might be <strong>the</strong> explanation for <strong>the</strong><br />
differ<strong>en</strong>ce in gibbsite cont<strong>en</strong>ts <strong>of</strong> <strong>the</strong> differ<strong>en</strong>t soil types.<br />
Vermiculite, chlorite and smectite are clay minerals which are abs<strong>en</strong>t or only pres<strong>en</strong>t in<br />
relatively small amounts in <strong>the</strong> TCP research area. area. Micas (illite) are moderately abundant in<br />
some soil samples, but no relation relation is found with <strong>the</strong> differ<strong>en</strong>t soil types. Feldspars and quartz<br />
are abs<strong>en</strong>t or only pres<strong>en</strong>t in small amounts <strong>the</strong> clay fractions.<br />
The iron hydroxide goethite is moderately abundant in all soils, whereas whereas <strong>the</strong> iron oxide hematite<br />
is abs<strong>en</strong>t in <strong>the</strong> three main soil types <strong>of</strong> <strong>the</strong> TCP area. Goethite is formed under a soil climate<br />
with suffici<strong>en</strong>t moisture in <strong>the</strong> dry season season ev<strong>en</strong> if <strong>the</strong> soils are well drained. It gives <strong>the</strong> soil a<br />
yellowish brown colour (Bilong, 1992). Driess<strong>en</strong> and Dudal (1989) (1989) state that goethite is formed<br />
wh<strong>en</strong> <strong>the</strong> iron conc<strong>en</strong>tration is low, <strong>the</strong> organic matter cont<strong>en</strong>t is high, <strong>the</strong> temperature is low<br />
and/or soil pH is lower than 4.0.<br />
5.4.6 Nutri<strong>en</strong>t cont<strong>en</strong>ts<br />
Combining bulk d<strong>en</strong>sity data data and chemical chemical data makes it possible to calculate <strong>the</strong> total total amounts<br />
<strong>of</strong> nutri<strong>en</strong>ts pot<strong>en</strong>tially available for plant growth. The data give an indication <strong>of</strong> <strong>the</strong> fertility <strong>of</strong><br />
<strong>the</strong> differ<strong>en</strong>t soils. The calculated nutri<strong>en</strong>t cont<strong>en</strong>ts for <strong>the</strong> three main soil types are averages <strong>of</strong><br />
four four to six pr<strong>of</strong>iles. Table 5.5. 5.5. shows <strong>the</strong> <strong>the</strong> nutri<strong>en</strong>t cont<strong>en</strong>ts cont<strong>en</strong>ts in kg/ha for a soil column <strong>of</strong> 1 meter<br />
deep. The majority <strong>of</strong> <strong>the</strong>se nutri<strong>en</strong>ts, however, are conc<strong>en</strong>trated conc<strong>en</strong>trated in <strong>the</strong> upper 20 cm <strong>of</strong> <strong>the</strong> soil<br />
pr<strong>of</strong>ile. pr<strong>of</strong>ile.<br />
The Nyangong soil has a relatively high nitrog<strong>en</strong> cont<strong>en</strong>t (12.5 ton/ha), whereas whereas available<br />
phosphorous and potassium are pres<strong>en</strong>t in relatively relatively small amounts <strong>of</strong> 8 and 360 kg respectively<br />
(Table 5.5.). Magnesium and calcium amounts are 195 and 1065 kg/ha, respectively. The Ebom<br />
soil has less less total nitrog<strong>en</strong> (8900 (8900 kg/ha), but a moderate amount <strong>of</strong> phosphorous (28 kg/ha). The<br />
Ebimimbang soil also has a moderate amount <strong>of</strong> available phosphorous (24 (24 kg/ha) but <strong>the</strong> total<br />
nitrog<strong>en</strong> nitrog<strong>en</strong> amount is low (7000 kg/ha). The pot<strong>en</strong>tially available K, Mg and Ca amounts are in <strong>the</strong><br />
same order <strong>of</strong> magnitude for all three soils.<br />
Table 5.5 5.5 Average nutri<strong>en</strong>t cont<strong>en</strong>ts <strong>of</strong> <strong>the</strong> Nyangong, Ebom and Ebimimbang soils in kg/ha kg/ha<br />
(soil column <strong>of</strong> <strong>of</strong> 1m)<br />
Soil type Total Total N Available P K Mg Ca<br />
Nyangong soil (n=6) 12500 8 8 360 195 1065<br />
(7371-24338) (3-16) (168-805) (168-805) (86-336) (607-1876)<br />
Ebom soil soil (n=4) 8900 8900 28 755 175 1785<br />
(5616-13022) (5-59) (361-1601) (60-306) (867-3558)<br />
Ebimimbang soil soil (n=6) 7000 24 370 165 165 1810<br />
( 4963-8757) (11-42) (11-42) (176-395) (27-535) ( (1295-2088) 1295-2088)<br />
The nutri<strong>en</strong>t nutri<strong>en</strong>t cont<strong>en</strong>ts <strong>of</strong> <strong>the</strong> soils in <strong>the</strong> TCP research area area are comparable with data data from o<strong>the</strong>r<br />
studies on on humid tropical forest soils (Anderson and Sp<strong>en</strong>cer, 1991; Gillman et al., 1985).<br />
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