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<Sourcebook of Alternative Technologies for Freshwater Augumentation in Africa>


1.4.3 Savanna Wetland Cultivation

Technical Description

This technique involves the cultivation of valley wetlands found in the plateau savanna regions of Africa (called dambos in southern Africa; Figure 24). Dambos are a multipurpose land and water resource being used for water supply, grazing and cultivation. Dambo catchments were thought to act as hydrological reservoirs, storing water in the rainy season and releasing it through evapotranspiration from the dambo surface and dry season stream flow. This was used as a basis for legislative protection of wetland but has not been supported by more recent hydrological investigations (Owen et al., 1995).

Figure 24. Dambo distribution in southern Africa (Bell et al., 1987).

 


Erosion plot and gully monitoring studies suggest that garden cultivation does not appreciably increase soil losses from dambos.

Figure 25

Figure 25. Dambo land use recommendations (Bell et al., 1987).

This technology may be called micro-scale irrigation and involves the utilisation of water around the periphery of a wetland using conventional agricultural methods (Figure 25).

Garden cultivation appears best suited to the upper wet zone of the dambo and should not normally exceed 10% of the total catchment area.

Extent of Use

Dambos are used for small- scale cultivation on farms ranging in area from 15 to 20 000 ha in Zimbabwe. Discouraged by colonial legislation, they have been developed entirely through local initiatives.

Operation and Maintenance

Depending upon the season, raised beds may be necessary to protect crops from water logging.

Level of Involvement

This technology is entirely farmer-initiated and managed.

Costs

There are no additional costs relative to conventional cultivation techniques incurred through the use of this technology.

Effectiveness of the Technology

Studies have shown that the upper dambo zone, which normally remains wet throughout the year, offers an insurance against years when rain-fed crops fail. Gardens on dambos provide food security through the production of staple crops, dietary variety through the production of vegetables, and also cash income to farmers and their families.

Suitability

This technology is suitable for shallow, seasonally-waterlogged depressions at the head of a drainage network. Such depressions are quite common and therefore this method is suitable for increasing crop production in these areas.

Environmental Benefits

Experiments carried out jointly by the University of Loughborough and the University of Zimbabwe have shown that there are no adverse environmental consequences.

Advantages

The small size of dambos (0.1 to 1 km wide by 0.5 to 5 km long) suggests that a small-scale approach is most suitable. It provide food security in years of poor rain-fed agricultural production and allows some dry season cultivation.

Disadvantages

Perceptions of environmental risk, which have not been dispelled by the limited data available, remain.

Cultural Acceptability

The practice has been developed by local people, who have no cultural problems with it.

Further Development of the Technology

There is a potential for considerable expansion of wetland cultivation in Africa which will probably require a clarification of the policy situation and removal of restrictive legislation. The impact on the environment should be investigated further.

Information Sources

Bell, M., R. Faulkner, P. Hotchkiss, R. Lambert, N. Roberts, and A. Windram 1987. The Use of Dambos in Rural Development, with Reference to Zimbabwe. Loughborough University, University of Zimbabwe.

Owen, R., K. Verbeek, J. Jackson, and T. Steenhuis (Editors) 1995. Dambo Farming in Zimbabwe: Water Management, Cropping and Soil Potentials for Smallholder Farming in Wetlands. Conference Proceedings. University of Zimbabwe, CIIFAD 193 p.

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