Chapter 3
Land resources (continued)

3.2 Soil Resources (continued)

TABLE 3.16
Extents of soil units

3.2.6 Soil Textures

Soil textures may vary within the range of textures defined for a particular soil unit. In the legend of the Exploratory Soil Map textural classes for individual soil units by soil mapping unit are presented. The three major textural divisions are subdived into 17 classes. The three major textural divisions are shown in the texture diagram.

Textural classes by major division are also listed below; percentage occurrence is presented in Table 3.17.

TABLE 3.17
Percentage occurrence of textural classes Texture class Texture Percentage

¹ Total extent where texture is applicable is 55 714 270 ha (96.9% of total area).

3.2.7 Soil Stoniness

The presence of coarse material (stoniness) in the soil profile has been inventoried separately from soil textures. The presence of coarse material is subdivided into six types:

Gravely (G)
Very gravely (VG)
Stony (S)
Bouldery (SB)
Stony/bouldery (SB)
Bouldery/stony (BS)

3.2.8 Soil Phases

Soil phases indicate land characteristics which are not considered in the definition of the soil units but are significant to the use and management of land. The soil phases recognized on the Exploratory Soil Map of Kenya can be grouped into phases indicating a mechanical hindrance or limitation (rocky, bouldery, boulder-mantle, stony, stone-mantle, gravel-mantle); phases indicating an effective soil depth limitation (lithic, paralithic, petro-calcic, piso-calcic, petro-ferric, piso-ferric); and phases indicating a physico-chemical limitation (saline, sodic and saline-sodic). Soil phases can occur alone (one soil phase or in combination (two or three phases). Some of these phases have been defined in the FAO-Unesco Legend, while others have been introduced in the Exploratory Soil Map. The soil phases and their extents are presented in Table 3.18.

3.2.9 Soil Mapping Unit Composition

At the exploratory level a soil mapping unit only rarely comprises a single soil; usually it consist of one main soil with minor associates. When the various soils of a soil mapping unit occur in a recognizable geographical pattern in defined proportions, they constitute a soil association; if such a pattern is absent, they form a soil complex.

The productivity potential of different soil units within a soil mapping unit consequently may vary widely. The suitability of soil association (soil complex) for specific use cannot be assessed without taking account of each individual soil unit within the association.

The legend of the Exploratory Soil Map does not provide explicit information in a quantified manner on the composition of the soil mapping units. This however has been provided to FAO by Stiboka in Wageningen in close cooperation with Kenya Soil Survey in Nairobi and the International Soil Reference and Information Centre in Wageningen (van der Pouw 1983).

The complete mapping unit composition table is presented in Technical Annex 1. This table consists of the percentage allocation of soil units by slope class, soil texture and soil phases for each soil mapping unit, and of information on landform and geology/parent material.

The composition of a example soil association (Ps3) is illustrated and explained in Figure 3.11.

3.3 Land Use Overlays

The land use and tse-tse infestation overlays have been integrated into the physical resources inventories. Consequently each agro-ecological cell is further characterized by the information contained in these overlays.

TABLE 3.18
Extents (%) of soil phases

¹ Total extent where soil phases occur is 28,096,674 ha (48.9 % of total area)

FIGURE 3.11
Example of soil mapping unit composition of soil mapping unit Ps3

TABLE 3.19
Extents of cash crop zones

TABLE 3.20
Extents of forest zones

TABLE 3.21
Extents of parkland areas

Tables 3.19, 3.20, 3,21, 3.22 and 3.23 present descriptions, map symbols, computer coding and extents of map units respectively of cash crop zones, forest zones, parkland areas, irrigation schemes and tse-tse infestation areas. Figures 3.12, 3.13, 3.14, 3. 15 and 3.16 present generalized maps of the above information and the details are presented in Technical Annex 3.

TABLE 3.22
Extents of initiation schemes

TABLE 3.23
Extent of tse-tse infestation areas

3.4 Computerized Land Resources Inventory

The computerized land resources inventory for Kenya records total extents of agro-ecological cells. Each cell contains information on the following:

-   Sequence number (NUM)

-   Province (PRV)

-   District (DIST)

-   Thermal Zone (TZ)

-   Length of Growing Period Zone (LGP)

-   Pattern of Length of Growing Period Zone (PAT)

-   Soil Mapping Unit (MPU)

-   Landform (LNDFM)

-   Geology/Parent Material (GEO)

-   Soil Unit (SOIL)

-   Soil Texture (TXT)

-   Soil Phases 1^st, 2^nd and 3^rd (PHASES)

-   Cash Crop Zone (CROP)

-   Forest Zone (FOR)

-   Irrigation Scheme (IRR)

-   Tse-tse Infestation Areas (TSE)

-   Parkland Area (PARK)

-   Extent in hectares (EXTENT).

The land resources inventory of Kenya consists of about 91 000 unique agro-ecological cells. For Kiambo District (code: 1) in Central Province (code: 1), the complete land resources inventory (651 cells) is presented in Technical Annex 1.

The computerized land resources inventory is available on diskettes (ASCII), in the form of a grid based geographic information system (GIS). For details on formats of the land resources inventory and the use of the geographic information system, reference should be made to Technical Annex 7.

FIGURE 3.12
Generalized map of cash crop zones

FIGURE 3.13
Generalized map of forest zones

FIGURE 3.14
Generalized map of parkland areas

FIGURE 3.15
Generalized map of irrigation schemes

FIGURE 3.16
Generalized map of tse-tse infestation areas