Africa is rich in both natural and human resources, yet nearly 200 million of its people are undernourished because of inadequate food supplies. Comprehensive strategies are needed across the continent to harness the power of science and technology (S&T) in ways that boost agricultural productivity, profitability, and sustainability -- ultimately ensuring that all Africans have access to enough safe and nutritious food to meet their dietary needs. This report addresses the question of how science and technology can be mobilized to make that promise a reality.
High-yielding varieties of a many different crops are commonly grown throughout the world. These varieties have been the key to a dramatic increase in yield, and formed the heart of the Green Revolution in Asia. The increase in harvest index (grain: total biomass ratio) from 0.3 to 0.5 caused this change. Furthermore, better growing conditions created more growth and therefore more total biomass. The full productivity rise due to these two major changes is only achieved in optimal growing conditions, eliminating the effects of growth- and yield-limiting and growth- and yield-reducing factors. When these prerequisites cannot be met, well-adapted landraces that may be less affected by the growing conditions are often less risky and preferred.
The proportions of farmers' fields planted with improved varieties in 1998 in Africa were around 40 percent for rice, 17 percent for maize, 26 percent for sorghum and 18 percent for cassava. Except for cassava, these were lower proportions than in Asia (about 65 percent for rice, 70 percent for sorghum) and Latin America (about 65 percent for rice, 46 percent for maize, 7 percent for cassava) (Evenson and Gollin, 2001). Until recently, the Green Revolution research paradigm in Africa has resulted in productivity gains mainly in farming/production systems that are most similar to the major cropping systems of Asia - namely the irrigated rice-wheat systems.
In Africa, where few farmers have access to either irrigation or affordable chemical inputs, and where growth- and yield-reducing factors contribute to large pre- and post-harvest losses, farmers' actual yields are typically a fraction of the genetic potential, even for their current varieties (De Jager et al., 2001). In this situation, research may be more efficiently directed at closing the yield gap by focusing on growth- and yield-limiting and growth- and yield-reducing factors. This research needs to address both technical and economic aspects. Technology-driven options require the development of varieties with properties such as salt tolerance and resistance to the prevailing pests and diseases. Moreover, given the diversity of production environments and farming systems, crop improvement research needs to use agro-ecological approaches that develop new varieties to fit into local niches, placing a premium on farmer participatory approaches (DeVries and Toenniessen, 2002). Research also needs to be directed at understanding and resolving factors that limit access to fertilizers, that make fertilizers use more efficient and that make irrigation more appropriate and less costly for small farmers. The latter research agenda includes work on technical, institutional and policy measurements and are addressed in further chapters.
CLIMATE AND WEATHER
The productivity potential of crops in Africa is quite high due to solar radiation and high temperature. Incoming radiation and temperature were once factors unaffected by humans, but that has changed in the last century. Scientific evidence on global warming points to a rise in average temperatures of 1.4-5.8 Celsius over the next century (Wilson, 2001). A sustained increase in mean ambient temperatures beyond 1 Celsius will cause significant changes in forest and rangeland cover, species distribution and composition, migration patterns and biome distribution. The African continent is particularly vulnerable to the impacts of climate change because of widespread poverty, inequitable land distribution, and high dependence on rainfed agriculture (IPCC, 2001). Most models predict more frequent and severe extreme weather events in the tropics generally, including both localized drought and flooding. Some drought episodes, particularly in southeast Africa, are associated with El Niño-Southern Oscillation (ENSO) phenomena, which have occurred more frequently in the last several decades.
Arid and semi-arid subregions and the grassland areas of eastern and southern Africa, as well as areas currently under threat from land degradation and desertification, are particularly vulnerable to global warming. A reduction in rainfall projected by some climate models for the Sahel and southern Africa, if accompanied by high inter-annual variability, could be detrimental to the hydrological balance of the continent and disrupt various water-dependent socio-economic activities. Variable climatic conditions may render the management of water resources more difficult, both within and between countries.
The productivity of coastal waters is dependent on ocean processes like upwelling, the health of mangrove forests, coral reefs, and seagrass beds and the amount and quality of runoff from the rivers. The western side of Sub-Saharan Africa includes some of the important upwelling ecosystems in the world. The wealth of estuaries, deltas, coastal lagoons, and coral reefs also contribute significantly to the diversity of fish life in the region (Koranteng, 2003).
Higher temperatures will also be accompanied by rising sea levels and more frequent occurrences of extreme weather events, such as flooding, droughts, and violent storms, causing changes in agricultural practices. Several African coastal zones, some of which already are under stress from population pressure and conflicting uses, would be adversely affected by sea-level rise associated with climate change. Of particular concern are the coastal zones of Angola, Cameroon, Gabon, The Gambia, Nigeria, Senegal, and Sierra Leone. Studies also indicate that a sizable proportion of the northern part of the Nile Delta could be lost to agriculture through a combination of inundation and erosion.
Climate change has particularly exacerbated soil degradation in the dry areas - pastoral, agro-pastoral, and sparse (arid) systems. Prolonged drought has already led to several ecological consequences, including (a) elimination of grass cover in some areas; (b) elimination of some bushes and acacia stands with shallow roots; (c) drop in the groundwater table, especially near wells and watering holes; (d) an increase in shifting sands; (e) increased wind erosion of fine soil components; and (f) increased evapotranspiration, accompanied by drying or cracking of soils (Oldeman, 1999). Recent evidence suggests that rainfall variability may be a more important determinant of the health of a rangeland and its soils than overgrazing (UNEP, 1997).