Land capability is a qualitative methodology to classify land resources basied on soil, topography and climate parameters without taking into account the yield and social economic conditions.
The classification is based on soil protection and it evaluates the most suitable kind of land use to achieve this target like rainfed agriculture, extensive grazing, or forestry.
According to Sys et al. (1991) the principles used for the capability classification are:
The conservation practices required aim to prevent chemical and physical soil degradation and to improve the soil's physical properties. This classification system is a general approach, not related to a specific land utilisation type.
The land capability classification identifies the eight classes described in Table 26 and the classes thresholds were slightly modified to fit better into the reality of the study area.
The parameters taken into account for land capability are reported in (*) L (Loam), SL (Sandy loam), LS (Loamy sand), Si (Silt), SCL (Sandy clay loam), SiCL (Silty clay loam), SiL (Silty loam), CL (Clay loam), SiC (Silt clay), SC (Sandy clay), S (Sand), and C (Clay).
Table 27. For soil texture, soil stoniness, available water capacity, pH, organic matter content, and carbonate a weighted average was done at a control section of 50cm. The "erosion" parameter comes from Van Zuidam (1986) erosion assessment (see chapter 4.3). Then all the factors were rated according to Table 26, ranging from 1 to 8. The land capability class was then ascribed to the highest value of the limiting factor.
Arable lands are included in class I to IV according to their potentiality and limitation for a sustainable agricultural system. Non arable lands, included from class V to VIII, are grouped in relation to their potential use for rangeland, forestry, and wildlife.
As a general comment land capability classification can be considered to perform the best result in land that is not yet cultivated and it’s more difficult to apply it on land already occupied.
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Class |
Description |
|
Class I |
soils that have slight limitations that restrict their use. |
|
Class II |
soils that have moderate limitations that reduce the choice of plants or require moderate conservation practices. |
|
Class III |
soils that have severe limitations that reduce the choice of plants or require special conservation practices, or both. |
|
Class IV |
soils that have very severe limitations that restrict the choice of plants or require very careful management, or both. |
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Class V |
soils that have little or no hazard of erosion but have other limitations, impractical to remove, that limit their use mainly to pasture, range, forestland, or wildlife food and cover. |
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Class VI |
soils that have severe limitations that make them generally unsuited to cultivation and that limit their use mainly to pasture, range, forestland, or wildlife food and cover. |
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Class VII |
soils that have very severe limitations that make them unsuited to cultivation and that restrict their use mainly to grazing, forestland, or wildlife. |
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Class VIII |
soils and miscellaneous areas that have limitations that preclude their use for commercial plant production and limit their use to recreation, wildlife, or water supply or for aesthetic purposes. |
Table 26 - Land capability classes and their description (modified from Landon, 1984)
The central part of study area (Figure 23), the plateau of Ben Slimane, results the best area for agricultural practices.
Some part of this area, characterised by Vertisols, is actually utilised for agriculture while the remaining part is covered by cork oak forest. The limitations of this area are due to many factors. The main ones are: the texture (clayey soils), the excessive presence of stones, and the poor drainage. For these reasons in the lands of the plateau it is impossible to find the first two classes of land capability but they are all included in class III or IV.
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Class |
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Parameters |
I |
II |
III |
IV |
V |
VI |
VII |
VIII |
|
Slope (%) |
0-2 |
0-2 |
4-10 |
11-32 |
>33% |
>33% |
>33% |
|
|
Evidence of erosion |
No sign to slight |
No sign to slight |
Moderate |
Moderate |
High |
High |
Very high |
|
|
Surface stoniness (%) |
0-5 |
6-14 |
15-39 |
40-79 |
>80 |
>80 |
>80 |
|
|
Soil stoniness(%) |
0-9 |
10-27 |
28-59 |
>60 |
>60 |
>60 |
>60 |
|
|
Soil depth (cm) |
>100 |
>80 |
>60 |
>40 |
>30 |
<30 |
<30 |
|
|
Soil drainage |
Never saturated |
Rarely saturated |
Rarely saturated |
Saturated for short period |
Saturated for long period |
Saturated for long period |
Saturated for long period |
|
|
Soil texture (*) |
L, SL, LS |
Si, SCL, SiCL, SiL, CL |
SiC, SC |
S, C |
Any |
Any |
Any |
|
|
Rock outcrops |
From very few to few |
Common |
Many |
Abundant |
Dominant |
Dominant |
Dominant |
|
|
Available water capacity |
>70 |
50=<x<=70 |
35<=x<50 |
20>=x>35 |
<20 |
<20 |
<20 |
|
|
Organic matter (%) |
>1 |
>0.8 |
>0.6 |
>0.4% |
>0.2 |
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|
Carbonate (%) |
0 |
<5 |
<20 |
>20 |
>20 |
>20 |
>20 |
|
|
pH |
6<=x<=8 |
6<=x<=8 |
5-6 or 8-9 |
5-6 or 8-9 |
<5 or >=9 |
<5 or >=9 |
<5 or >=9 |
|
(*) L (Loam), SL (Sandy loam), LS (Loamy sand), Si (Silt), SCL (Sandy clay loam), SiCL (Silty clay loam), SiL (Silty loam), CL (Clay loam), SiC (Silt clay), SC (Sandy clay), S (Sand), and C (Clay).
Table 27 - Land capability factors (modified from Landon, 1984)
In class IV the limiting factors are also the insufficient presence of organic matter, the excess of carbonates and the inadequate depth of soils.
The western scarp area has the same characteristics as the plateau for land capability, but where the slope increases the class capability changes to VI or VII like in land unit 20 and 21.
Southern reliefs, currently exploited with poor agriculture, are included in class VI principally becouse of the steepness of the slopes. The same restrictions are present in the eastern scarp area. This region is mainly covered with a plantation of Pinus halepensis and is not suitable for agriculture.