[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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The pH2 <strong>of</strong> <strong>the</strong> Nyangong Nyangong topsoils topsoils and subsoils subsoils is in <strong>the</strong> range <strong>of</strong> 3.5 to 4.5 (extremely (extremely acid).<br />
Khanna and Ulrich (1984) (I 984) define <strong>the</strong> pH range 3.8-4.2 as <strong>the</strong> aluminum buffer range, which<br />
means that aluminum is exchanged against hydrog<strong>en</strong> with decreasing pH.<br />
The pH <strong>of</strong> <strong>the</strong> Ebom soils is 3.5-5 in <strong>the</strong> topsoils and 4-5 in <strong>the</strong> subsurface horizons (very<br />
strongly to extremely acid). The pH values <strong>of</strong> <strong>the</strong> Ebom soils are only slightly higher than those<br />
<strong>of</strong> <strong>the</strong> Nyangong soils, and <strong>the</strong>y are intermediate betwe<strong>en</strong> <strong>the</strong> Nyangong and Ebimimbang soils.<br />
The pH values <strong>of</strong> <strong>the</strong> Ebimimbang topsoils are 1-1.5 units higher than those <strong>of</strong> <strong>the</strong> Nyangong<br />
and Ebom soils. The topsoil pH is 5-6 (medium to strongly acidic), and <strong>the</strong> subsurface soil pH<br />
is 4.5-5.5 (strongly to very strongly acid). This marked gradi<strong>en</strong>t in pH with depth is<br />
characteristic for soils in <strong>the</strong> cation exchange capacity buffer (4.2-5). Cations are exchanged<br />
against hydrog<strong>en</strong> to buffer changes in pH. Soils with pH values within this range are<br />
characterized by sharp differ<strong>en</strong>ces in chemical characteristics (Khanna and Ulrich, 1984), which<br />
is confirmed by <strong>the</strong> base saturation data <strong>of</strong> Ebimimbang topsoils and subsurface horizons.<br />
The Valley Bottom soil has pH values that resemble those <strong>of</strong> <strong>the</strong> Ebimimbang soil. The topsoil<br />
pH is betwe<strong>en</strong> 5 and 6 and <strong>the</strong> subsurface pH is betwe<strong>en</strong> 4.5 and 5.5.<br />
All subsoils have pH values betwe<strong>en</strong> 3.5 and 5.5. In <strong>the</strong>se pH ranges manganese (Mn),<br />
aluminum (AI), iron (Fe) and trace elem<strong>en</strong>ts as copper (Cu), zinc (Zn) and borium (B) are<br />
available for plant growth (Euroconsult, 1989; Landon, 1991). In g<strong>en</strong>eral <strong>the</strong> aluminum<br />
conc<strong>en</strong>trations <strong>of</strong> <strong>the</strong> soils in <strong>the</strong> TCP research area are high and exchangeable potassium (K),<br />
magnesium (Mg) and calcium (Ca) conc<strong>en</strong>trations are very low in <strong>the</strong> soil solution (see Table<br />
5.4b.). Crops grown on <strong>the</strong>se soils may experi<strong>en</strong>ce nutri<strong>en</strong>t defici<strong>en</strong>cies. High aluminum<br />
conc<strong>en</strong>trations in <strong>the</strong> soil solution are toxic to many crops. Low pH values as found in <strong>the</strong><br />
Nyangong soils, facilitate <strong>the</strong> formation <strong>of</strong> iron and phosphate aluminium compounds. This<br />
phosphate phosphate is not available to plants. The somewhat higher topsoil pH values might be explained<br />
by rec<strong>en</strong>t agricultural activities which include <strong>the</strong> burning <strong>of</strong> vegetation by which alkaline ashes<br />
are are formed. formed.<br />
5.4.2 Organic carbon and total nitrog<strong>en</strong><br />
The organic carbon and related total nitrog<strong>en</strong> cont<strong>en</strong>ts <strong>of</strong> <strong>the</strong> topsoils differ significantly<br />
betwe<strong>en</strong> betwe<strong>en</strong> <strong>the</strong> <strong>the</strong> four four soil soil types. types. The The observed observed organic organic carbon carbon range within within <strong>the</strong> survey survey area area is 2%-9% 2%-9%<br />
and <strong>the</strong> total nitrog<strong>en</strong> cont<strong>en</strong>ts range from 0.15%-0.5%. The topsoils have significantly higher<br />
organic organic carbon carbon and and total total nitrog<strong>en</strong> nitrog<strong>en</strong> cont<strong>en</strong>ts cont<strong>en</strong>ts than <strong>the</strong> subsoils. subsoils. Fig. 5.2. shows shows <strong>the</strong> <strong>the</strong> relation relation betwe<strong>en</strong> betwe<strong>en</strong><br />
organic carbon and total nitrog<strong>en</strong> conc<strong>en</strong>trations for for all all samples. The The CIN value calculated with<br />
regression regression analysis analysis on all data is 13 (R2 = 0.94).<br />
The Nyangong topsoils have organic carbon cont<strong>en</strong>ts betwe<strong>en</strong> 4% and 9% and total nitrog<strong>en</strong><br />
cont<strong>en</strong>ts betwe<strong>en</strong> 0.25% and 0.4%. The CIN values <strong>of</strong> <strong>the</strong> topsoils are betwe<strong>en</strong> 12 and 18. The<br />
subsurface horizons have organic carbon cont<strong>en</strong>ts betwe<strong>en</strong> 1 1% % and 3 3% % and total nitrog<strong>en</strong><br />
cont<strong>en</strong>ts betwe<strong>en</strong> 0.1 % and 0.15% (Table 5.4a.). In <strong>the</strong> subsoils <strong>the</strong> organic carbon cont<strong>en</strong>t drops<br />
rapidly to below 0.5%. The CIN values <strong>of</strong> <strong>the</strong> subsurface horizons are in <strong>the</strong> range <strong>of</strong> 10 to 14.<br />
2 With pH, we mean pH(H 20), 20), unless o<strong>the</strong>rwise indicated.<br />
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