1t0SC7l

nutrients (Mn, B, Zn, Cu, etc.) remain in the ash (see Section 3.3.2). Nutrients stored in the ash
layer are mobilised during periods of rainfall and are transferred to the soil by percolating water
or washed away by sheet erosion. In the soil, part remains available for crop nutrition and crop
removal while another part is leached. Decomposition of soil organic matter, combined with a
lack of fresh input of organic matter, result in decreasing C and N content during the cropping
period (see Section 3.3.2).
pH
Organic Carbon
7
6
pH
5
4
%
4
3
2
1
3
YCA OCA FV
FV YOP YANA
0
YCA OCA FV
FV YOP YANA
Land Use types
Land Use Types
Available P
Sum of Bases
15
10
P (ppm)
12
9
6
3
Bases (cmol/g)
8
6
4
2
0
YCA OCA FV
FV YOP YANA
0
YCA OCA FV
FV YOP YANA
Land Use Types
Land Use Types
Total acidity
Bulk density
Acidity(Cmol/g)
7
6
5
4
3
2
1
0
YCA OCA FV
FV YOP YANA
Density (g/cm3)
1.6
1.4
1.2
1.0
0.8
YCA
OCA FV
FV YOP
YANA
Land Use Types
Land Use Types
0,8 1,2 1,4 1,6
1
0-10 (Ebim) 10-20 (Ebim) 0 -10 (Nyan) 10-20 (Nyan)
Figure 3.8. Some soil chemical and physical property changes under perennial crop and sole annual crop
compared to virgin forest.
Keys: YCA= Young cocoa plantations (4 to 7 year old); OCA = Old Cocoa plantations (more than 15 year
old); YOP= Young mature oil palm plantation; YANA= Pineapple field (sole annual crop); FV =
Virgin Forest (control); Ebim = Ebimimbang soils; Nyan = Nyangong/Ebom soils.
Physical changes in soils. During the cropping phase of the shifting cultivation as practised in the
area, the direct impact of rain drops and sunshine on exposed soil results in increased rain splash
and subsequent sheet erosion. This, combined with a decrease in organic matter content of the
43