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4.2.2 Land suitability for crops and fruit trees

The study area is mainly cultivated with durum wheat, wheat, barley, oat, bean, and white lupin. While wheat and beans are used as grain crops, the others are used as fodder crops. Other food crops are onion and chickpea that represent a widespread reality even in small surfaces. The plateau of Ben Slimane is the most suitable land system for agricultural purposes due to the flat or almost flat geomorphology. Here the highest yields of the area were found, especially for wheat (60q/ha). As described in the agricultural section (3.3 Land use and vegetation

A very general overview of the main land use and land cover of the study area is given Figure 18.

3.3.1) the farming system is quite simple, only fertilisation is common, while irrigation is found only in fruit tree plots along the Oued Nefifikh.

The study area is characterised by the presence of olive, grape and pomegranate plantations and ,as said in the agricultural section, fruit trees, could be exploited in a better way, but the agricultural management should pay more attention to fertilisation, chemical treatments, soil management and irrigation scheme development, where possible.

The water scarcity is always a problem in the area and it is the most limiting factor for intensive agricultural exploitation.

Given the above considerations, the Ben Slimane province land suitability assessment aims to achieve the following objectives:

Methodology

The methodology used for the evaluation refers to the Sys et al. parametric method (1991), based on F.A.O land evaluation framework (1983) for rainfed agriculture. Crop requirements are further adjusted to fit better with the Ben Slimane province.

The methodology consists in matching land characteristics against crop needs and assigning a suitability rating to each land characteristic. The method includes a first analysis of climatic data, like radiation, temperature, rainfall, and relative humidity, but due to the lack of data, the climate was considered homogeneous and suitable for all the analysed species.

Terrain and soil parameters taken into account are shown in Table 36. Values of ratings, as suggested by Sys et al. (1991), were slightly modified to match the characteristics of the study area. A weight was assigned to each parameter to point out the pressure of that characteristic in the evaluation process.

With the exception of soil depth, on soil parameters a weighted average was performed according to the root depth (control section) of each plant (Table 37).

Terrain

Soil

Slope (%)

Drainage

Rock outcrops (%)

pH

Surface stoniness (%)

EC (dS/m)

CaCO3 (%)

Depth (cm)

CEC (cmol(+)/kg soil)

Organic carbon (%)

Texture

Table 36 - Terrain and soil parameters used in land suitability assessment

Agricultural crops

Control section (cm)

Wheat

60

Barley

60

Sorghum

50

Chickpea

70

Onion

40

Safflower

75

Olive

120

Grape

80

Table 37 - Crops and corresponding control section

In line with 20th IAO Course final report (2000, not published), done in Tunisia, the mathematical method adopted to process all data was based on a formula, which was built up mixing the sum and the product of the parameters according to their weight. It was verified that this method was more powerful to assess the land suitability. The formula is reported below.

Results and discussion

For a more homogeneous analysis of the results, it is useful to subdivide the study area in the four land system.

The region of plateau is currenctly utilised mainly for agriculture. This area appears the most suitable for cultivation, with quite a good adaptability for all the species analysed.

Particularly for food crops, in the plateau of Ben Slimane, the suitability classes are the same for predominant land units. The range of suitability varies from S2 to N. For wheat the class S1 is found only in land unit 1 (Table 38). The other food crops have a low value due to the difference in the selected control section. For all the three species the predominant suitability class is S2 and the second most important class is S3 (Table 38).

Adaptability condition for fodder crops is wider, so it is possible to find more land units in class S1 and S2, both for barley and sorghum.

For fruit trees the conditions are slightly more suitable for olive trees than for vineyards. The most suitable locations for olive trees are in flat areas with vertisols and in undulating areas with plinthosols. The high adaptability of this plant is related to the low requirement of the species.

In the western scarp the predominant lands are not suitable for food crops (Table 38), but have a high value for fodder crops and for tree crops. For fodder crops some land units are ascribed to class S1 (Table 39), while land unit 20 and 21 are never suitable for all kind of crops (Table 38-Table 41).

In the eastern scarp the main limiting factors are the geomorphologic characteristics and the land units could only be utilised for sorghum (Table 39) and safflower cultivation (Table 41).

In the southern hills conditions are moderately better. The cultivation of food and fodder crops is possible only in some small areas where erosion process is limited and the soil is not degraded (Table 38 and Table 39); some limitations for fruit trees are also present (Table 40).

Finally it is very interesting to note the high safflower adaptability that can be developed as an interesting and profitable alternative. Table 41 shows a good adaptability of the species in all the land systems.

Figure 25 shows the crop surface distribution in relation to the suitability classes.

The suitability maps for the different crops are shown in Figure 26 - Figure 33.

Land system

Land Unit

Onion

Chickpea

Wheat

Area (km2)

Plateau

1

S2

S3

S1

87.41

2, 3, 17, 18

N

N

N

11.82

4

N

N

S3

7.78

5, 16

S3

S3

N

135.90

6, 7, 8, 9, 10, 11, 12, 13, 14, 15

S2

S2

S2

135.82

Western scarp

19, 20, 21

N

N

N

49.42

22

S2

S2

S2

4.68

23

S1

S2

S1

0.73

Eastern scarp

24, 25, 26, 27, 28

N

N

N

41.59

Southern reliefs

30

N

N

S2

5.40

31

S2

S2

S2

6.17

29, 32, 33, 34, 35, 36, 37

N

N

N

120.12

Table 38 - Land suitability for food crops

Land system

Land Unit

Barley

Sorghum

Area (km2)

Plateau

1, 6, 13

S2

S1

130.19

2, 3, 7, 15, 17, 18

N

N

11.70

4

N

S2

7.78

5, 8, 16

S3

S2

143.68

9, 11, 14

S2

S2

46.74

10, 12

S3

S3

37.24

Western scarp

19

N

S3

38.86

20, 21

N

N

43.05

22

S2

S1

4.68

23

S1

S1

0.73

Eastern scarp

24

N

S3

8.76

25, 26, 27, 28

N

N

32.83

Southern reliefs

30

S2

S2

5.40

31

S2

S1

6.17

29, 32, 33, 34, 35, 36, 37

N

N

120.12

Table 39 - Land suitability for fodder crops

Land system

Land Unit

Olive

Grape

Area (km2)

Plateau

1

S1

S3

87,41

2, 3, 4, 10, 12

S3

N

51,68

6

S2

S2

24,63

8

S1

S2

7,779

9, 11, 13, 14

S2

S3

64,89

7, 15, 17, 18

N

N

5,04

5 16

S3

S3

135,90

Western scarp

19

S2

S3

38,86

20 and 21

N

N

43,05

22

S1

S2

4,68

23

S1

S3

0,73

Eastern scarp

24, 25, 26, 27, 28

N

N

41,59

Southern reliefs

29, 32, 33, 34, 35, 36, 37

N

N

120,12

30

S2

S3

5,40

31

S2

S2

6,17

Table 40 - Land suitability for fruit trees

Land system

Land Unit

Safflower

Area (km2)

Plateau

1, 10, 12

S3

124.65

2, 3, 7, 15, 17, 18

N

11.70

4, 5, 6, 8, 9, 11, 13, 14, 16

S2

233.19

Western scarp

19, 20, 21

N

49.42

22, 23

S1

5.41

Eastern scarp

24

S3

8.76

25, 26, 27, 28,

N

32.83

Southern reliefs

29, 32, 33, 34, 35, 36, 37

N

120.12

30

S3

5.40

31

S2

6.17

Table 41 - Land suitability for safflower

Figure 25 - Crops surface distribution in relation to suitability classes

Figure 26 - Land suitability for onion

Figure 27 - Land suitability for chickpea

Figure 28 - Land suitability for wheat

Figure 29 - Land suitability for barley

Figure 30 - Land suitability for sorghum

Figure 31 - Land suitability for olive tree

Figure 32 - Land suitability for vineyards

Figure 33 - Land suitability for safflower


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