Matching technologies to agricultural regions

The most appropriate technologies to use will vary from place to place depending on a wide range of circumstances. A broad classification may be made based on climate, Figure 2, and the traditional agricultural background of local people. Table 3 links technology options to agricultural regions and Table 4 links them to countries.

Irrigation has been associated with the flood plains of large perennial rivers. Major examples include the Niger River in Niger, Mali and northern Nigeria, the Senegal River in Mauritania and Senegal and the Juba and Shebelli Rivers in Somalia. Outside the region the Nile in Sudan and Egypt is famously associated with irrigation. These areas have always been prime sites for large-scale irrigation schemes and have long traditions of smallholder irrigation. For instance, in Niger, during the wet season, floating rice is planted in the riverbed at the beginning of the rains and is flooded as the river rises. Later, from November to April, small vegetable gardens are cultivated on the riverbanks and alluvial terraces that are not flooded during peak flow in January-February. When the floods recede crops such as sweet potatoes, maize and onions are planted and irrigated from shallow groundwater. Small pumps are gaining increasing acceptance in many countries wherever spare parts and fuel are readily available.

Desert and semi-desert

This zone is characterized by very low, erratic rainfall (less than 500 mm per annum), which renders purely rainfed agriculture impossible. The major agricultural activity is nomadic stock raising with camels, goats, sheep and cattle being the principal stock. In this zone the most important form of smallholder irrigation development is likely to be water harvesting. Spate irrigation could also be practised in occasional watercourses as well as shallow groundwater development.

In some places such practices are traditional. For example, in the Lower Omo Valley in Ethiopia, (rainfall 300 mm/year), fodder and food crop production depends almost entirely on seasonal floodwater from the River Omo and recession farming in the old river channels. Successful systems of run-off farming have also evolved in the adjacent Woito Valley.

The techniques of run-off agriculture are still at an experimental stage in Africa (see Tanzania box). The success of smallholder schemes in these regions is to a large extent dependent on the acceptability of settlement to the nomadic tribes who generally populate this area. Without their enthusiastic cooperation any irrigation development is likely to be unsuccessful.

Water harvesting is the only alternative to making a living through semi nomadic stock raising or famine relief. Where these semi nomadic people have become destitute, as is happening in vast areas of Ethiopia and Somalia, they may be prepared to settle on permanent smallholder irrigation schemes. The future prospects for this zone are not promising because of the increasingly tight definitions of boundaries and territories and continuing encroachment of agriculture into traditional pastures.

An example of the establishment of water harvesting by semi-nomadic tribes was in Turkana in northern Kenya in the early 1980s. There were reports of local resistance in the form of apathetic attitudes and inherent scepticism towards the idea that crops could be produced on what was traditionally regarded as grazing land. Once there was demonstrable success in increasing fodder production the level of participation grew rapidly and a large number of fields were under regular cultivation producing grain, fodder and wood.

Dry savannah agriculture

This zone extends over large areas of Africa. It differs from the desert and semi-desert zone in having a higher annual rainfall of 500-600 mm (occasionally up to 1 000 mm) which falling in a single three to six month long rainy season. The main form of agriculture is sedentary stock raising in some areas and arable farming in others. The types of irrigation likely to succeed in these areas are water harvesting and irrigation of river flood plains and other extensive plains, either in the wet season with bunds to control occasional floodwaters or with exploitation of shallow groundwater throughout the year.

An example of successful run-off agriculture comes from Burkina Faso where an NGO initiated a combined agro-forestry and water-harvesting project. In 1979 a small experimental area of micro catchments for fuelwood trees was established with farmer participation. The farmers involved subsequently adopted these runoff-farming techniques and used them to improve their traditional erosion control methods, thus increasing their normal agricultural production. Fields long abandoned are being reclaimed and farmers are increasing infiltration through the construction of simple contour bunds.

Humid savannah agriculture

In this zone the annual rainfall is normally between 1 000-2 000 mm falling either in two rainy seasons close to the equator or as one long rainy season further north or south. This is sufficient to grow two rainfed crops in countries close to the equator (e.g. Rwanda, Burundi, Central African Republic) and one rainfed crop in more northerly or southerly areas. The role of irrigation in this zone is therefore to (a) improve the yields of existing crops, such as maize, groundnuts and cotton, (b) by reducing risks; extending the length of the growing season or allowing a second (or third) crop to be produced in the dry season, and (c) allowing new areas of land to be developed for crop production through drainage of swampy areas for dry season cropping or water control for wet season rice growing.

In general, in countries with adequate agricultural land reserves, the main emphasis should be primarily on the development of improved agronomic techniques in rainfed agriculture. However, where the available agricultural land is scarce and the population pressure is high there will be an inevitable acceleration in the development of irrigation. Rwanda is a prime example of this with an average population density over 200 persons/km².

The physical types of irrigation will largely depend on the topography of the areas but most irrigation will be on river flood plains or extensive plains. Emphasis will be on supplementary irrigation in the dry season, followed by control of water in the wet season for rice cultures. Irrigation of small areas from channels and non-seasonal irrigation in flood plains and extensive plains will be important in localised areas.

Humid tropical forest agriculture

This zone is the wettest region with annual rainfall in excess of 1 500 mm, usually falling in two main wet seasons. This zone therefore differs from others in that it is wet throughout most of the year and has no major constraints to rainfed agriculture, except during the short intervening dry season. The major irrigation issues will be concerned with water control and drainage rather than with irrigation per se, although supplementary irrigation can be practiced particularly for crops, such as vegetables grown in the short dry season as in parts of Nigeria. The most important will be small areas commanded from weirs and channels, such as the inland valley swamps of Sierra Leone, Liberia and Guinea. In the wet season, deep-water rice may be grown in the same small swamps. In Togo and Benin the main form of irrigation will involve small to medium sized earth dams commanding the downstream areas by channels and with various lifting techniques, for irrigating upstream of the dams. In coastal regions there are large areas of rice grown in the mangrove swamps and in river estuaries during the wet season. Sierra Leone has 20 000 ha of mangrove swamps cropped with a potential for 74 000 ha.

High tropical and subtropical plateau agriculture

The high tropical and sub tropical plateaus, which are greater than about 1 500 m above sea level are characterized by low temperatures, particularly in the cool seasons away from the equator, which can restrict the choice of crops. Rainfall varies from 500 mm/year upwards.

The most suitable form of irrigation will vary depending on topography and rainfall but will generally involve small areas commanded by channels. In the high veld of Zimbabwe many small farm dams have been constructed in small catchments that are used for smallholder irrigation and stock watering. The techniques employed in Zimbabwe tend to use modern technology with sprinkler irrigation being very important. In the Rumphi district of Malawi small channels are lead away from streams to suitable areas for irrigation, which may be several kilometres away. In many of the areas (e.g. South Tanzania, Zambia, Malawi), supplementary irrigation of cash crops such as tea and coffee during the extended dry season is practised commercially and opportunities exist to extend this to smallholder schemes.

Figure 2: Agricultural regions of Africa in relation to smallholder irrigation

Source: Kay et al 1985

Table 3: Relative importance of small-scale irrigation in agricultural regions

Region	River flood plains			Swamp irrigation	Hill irrigation	Rainwater harvesting
	Wet season	Dry season	Groundwater
Desert and semi-desert			2			1
Dry savannah agriculture	2		2			1
Humid savannah agriculture	2	1	3		3
Humid tropical forest agriculture	3	1		3	1
Pastoral stock raising						1
Semi-nomadic stock raising						1
High tropical and sub-tropical Plateau agriculture					1
Irrigated agriculture	2	1	3

NOTE 1 very important, 2 fairly important, 3 less important
Source Kay et al 1985

Table 4: Summary of smallholder irrigation technologies by country

Country	River flood plains			Swamp irrigation	Hill irrigation	Rainwater harvesting
	Wet season	Dry season	Groundwater
Angola
Benin
Botswana
Burkina Faso
Burundi
Cameroon
Central African Republic
Chad
Congo
Congo Dem Rep
Cote d'Ivoire
Equatorial Guinea
Ethiopia
Gabon
Gambia
Ghana
Guinea
Guinea Bissau
Kenya
Lesotho
Liberia
Malawi
Mali
Mauritania
Mauritius
Mozambique
Namibia
Niger
Nigeria
Rwanda
South Africa
Senegal
Sierra Leone
Somalia
Swaziland
Tanzania
Togo
Uganda
Zambia
Zimbabwe