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Irrigation and drainage
Evolution of irrigation development
Sierra Leone’s irrigation potential was estimated at 807 000 ha in 1981 (Table 4). The breakdown of cultivable land into upland and lowland is given in Table 5. It shows the relative importance of the four classes of lowlands, with a total area of 1.165 million ha: inland valley swamps (IVS), bolilands which are drainage depressions, mangroves in the coastal tidal zone, and annually flooded riverine grasslands. It should be noted, however, that these 1.165 million ha correspond to the total area of lowlands. Lowland suitable for development is about 807 000 ha, corresponding to the above irrigation potential, leaving aside environmental aspects.
Irrigated agriculture is poorly developed in Sierra Leone, and no recent data on its extent are available. Generally, areas with good water control and having the possibility of more than one crop a year are very limited. In 1992, 1 000 ha were reported to be irrigated for sugar cane production and 28 360 ha of wetland had been equipped for rice cultivation, although most of it was not operational. Thus the area equipped for irrigation was 29 360 ha in 1992. In 1992, 126 000 ha of non-equipped wetlands and inland valley bottoms were cultivated, bringing the total water managed area in 1992 to 155 360 ha (Table 4 and Figure 2).
Simple drip irrigation systems (bucket & hose type) are currently being introduced to Sierra Leone by an NGO, which distributed about 500 kits in 2003 after test systems met with approval. The NGO plans to ship another about 4 000 kits to the country.
Role of irrigation in agricultural production, the economy and society
The main irrigated crop is rice, and five principal rice ecosystems are generally identified:
- Rainfed upland, where most rice is produced (about 64 percent of total national rice area).
- Inland valley swamp (IVS), accounting for another 26 percent of the total area under rice. Only a small portion, less than 5 percent, of the inland valley swamp rice area has been developed, permitting partial water control.
- Coastal mangrove swamp.
- Bolilands, which are lowland depressions in the interior that are seasonally flooded and are generally characterized by fragile soil fertility.
- Riverine grassland (deepwater), which is also seasonally flooded, but with much better fertility characteristics than the bolilands.
The reduced fallow period, induced by increasing population pressure, has had adverse impacts on the soil fertility for upland cropping. The IVS have relatively more fertile soils than the upland areas and can support a higher cropping density. Although the government has attempted to develop double cropping of rice by developing the IVS for irrigation, the high cost of development and weak extension capability has so far made this option unsuccessful.
Rice yields in traditional wetland are about 1.5 tonnes/ha, while in upland areas they are around 1 tonne/ha. In farmer-managed demonstration plots, yields reach an average of 3.2 tonnes/ha. The other two main crops grown in wetlands, namely cassava and sweet potato, have an average yield of 2.2 tonnes/ha and 2.7 tonnes/ha respectively.