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Because the focus was on agricultural land-use planning, it was assumed that land- utilization types of the preservation forest and settlement area were static.
4. Results
4.1. Erosion hazard analysis
Comparison between estimated soil loss and tolerable soil loss generated an erosion hazard map of the Cianjur watershed, based on current agricultural land-use
Fig. 7 , that
identified the erosion hazard area where intolerable soil loss was predicted. This area was grouped into four classes that indicated how urgently management was needed. Estimated soil
loss for the watershed under current agricultural land-use ranged from 0 in flat forest areas to 344 t ha
−1
year
−1
in very steep areas of Vegetable dry fields; tolerable soil loss ranged from 25 to 60 t ha
−1
year
−1
. Although no significant erosion estimated soil loss tolerable soil loss was predicted in 4416 ha 74 of the watershed area, estimated soil loss was predicted to exceed
tolerable soil loss on 1219 ha 26 of the watershed area; in some areas covering 466 ha, mostly utilized as Vegetable dry field estimated soil loss was very high 200 t ha
−1
year
−1
. The relationship between land-utilization type and estimated soil loss in current agricultural land-use
is summarized in Table 2
, particularly for current agricultural land-use. The results indicate that practiced Vegetable dry field and Starchy crop dry field urgently required better land
management practices in terms of cropping and management factor and conservation control practice factor.
Full-size image 38K
Fig. 7. Erosion hazard map. ESL: estimated soil loss and TSL: tolerable soil loss. Table 2.
Relationship between land-utilization type, estimated soil loss and tolerable soil loss in current agricultural land-use
Land-utilization type
Range of
estimated soil
loss t ha
−1
year
−1
Range of
tolerable soil
loss t ha
−1
year
−1
Paddy field 1 0.6
–78.0 43
–60
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Land-utilization type
Range of
estimated soil
loss t ha
−1
year
−1
Range of
tolerable soil
loss t ha
−1
year
−1
Paddy field 2 0.5
–26.1 36
–50 Tea plantation
4.9 –167.3
35 –45
Vegetable dry field 12.8
–344.2 25
–50 Starchy crop dry
field 12.8
–341.9 35
–50 Mixed garden 1
4.1 –184.7
25 –40
Mixed garden 2 3.9
–164.9 35
–43 Forest garden
0.1 –85.5
25 –38
In cases where the current land-utilization type caused significant soil loss, land management practice improvements and land-utilization-type conversions were considered that could reduce
soil loss. The following measures are listed in order, starting with the most preferred measure, according to the convenience of application: 1 alteration of the cropping and management
factor through adoption of a minimum tillage system. 2 Alteration of the conservation control practice factor through better conservation control practices. For instance, an irregular strip
planting system should be changed to a contour planting strip planting across the slope and hedgerow system. 3 Land-utilization-type conversion or alteration of the slope length and
steepness factor by terracing; both of these last two options are last choices, considering the high investment and potential social constraints.
4.2. Land suitability analysis
