Friday, May 27, 2011

Enough land, enough water

Sub-Saharan Africa (SSA) has enormous potential for developing and increasing rice production. There is tremendous scope for developing rainfed lowland rice areas, augmenting the area under irrigation, and raising yield levels in farmers’ fields through diffusion and adaptation of rice technology to local conditions.

The total area of land potentially suitable for crops in Africa is estimated to be 874 million ha (Mha), but only 150 million ha is harvested yearly. According to the United Nations Environment Program (UNEP), Africa only uses about 4% of its water resources.

In SSA only 3% of crop land is irrigated (representing 5 Mha). The total irrigation potential in the principal river basins of SSA amounts to 35 Mha. Therefore, there are still abundant untapped opportunities to expand rice production in SSA for a versatile crop such as rice that can be grown across a wide range of agro-climatic zones.

Rice in Africa is mainly grown under rainfed conditions, unlike Asia, where 55% of rice is grown under irrigation. From the about 8.4 Mha of land under rice cultivation in SSA in 2007, about 40% is located in the upland ecology (contributing 19% to total rice production), 37% in the rainfed lowland ecology (contributing 48% to total rice production) and 14% in the irrigated ecology (contributing 33% to total rice production). The remaining 9% is covered by deep-water and mangrove rice.

Upland rice farming is constrained by frequent drought, low soil fertility (due to deficiencies of nitrogen and phosphorus) and soil acidity. Weed competition constitutes the most important yield-reducing factor, followed by drought, blast, soil acidity and low soil fertility. Many of the poorest rice farmers depend on the upland ecology. Typical average rice yield under upland growth conditions is about 1 t/ha. With the use of robust varieties, and improved management practices to rebuild soil fertility and capture rainwater, there is potential to increase yields in the uplands by 2 to 4 t/ha.

Lowland rice cultivation offers great prospects for expansion, intensification and diversification. Estimates of available rainfed lowland areas range between 138 Mha and 238 Mha. The soils in lowland ecologies are generally less fragile and floodwater conditions promote the growth of nitrogen-fixing bacteria and blue-green algae that produce enough nitrogen to sustain 3 t/ha rice yield year after year.

The main constraints to rice production are water control and weed management. The attainable yield is from 3 to 6 t/ha, while the actual yield is typically between 1 and 3 t/ha. Rainfed lowlands also have great potential to diversify rice systems, e.g. by growing vegetable crops after rice, or through combined rice-fish culture.

Irrigation for rice comes in many different forms in SSA and ranges from small (20 ha) stream diversion based systems to large (>10,000 ha) gravity or pump-based systems. Though developing new large irrigated rice schemes may perhaps not be possible, there is much scope for using the potential of existing irrigation infrastructure.

For instance, the substantial yield increases achieved in the Sahel (Mali and Senegal), show that irrigated rice is a feasible option in the sub-region. Attainable rice yields with full water control are in the range of 7 to 9 t/ha, while actual paddy yields on farmers’ fields are from 3 to 6 t/ha.

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