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.
In the previous section, the trends in development of the farming systems in terms of land, labour and fertilizer productivity were analyzed. Specific analysis of productivity in systems is virtually impossible, but yield gap analyses can be presented on a commodity basis. A generic analysis of yield gaps using production ecological principles in terms of grain equivalents is presented for the countries south of the Sahara in Box 4.1. Unfortunately no commodity-specific analyses using this concept are available for Africa. Therefore, other measures of yield gaps are used for various commodities based on readily available information from field and farm experiences, as yield gaps can also be expressed using best farmer practice or best experimental practice (See Box 3.3, Chapter 3).
On average, yields, expressed in grain equivalents, could increase by 3-5 tonnes per hectare in semi-arid regions growing one crop per year, and by 13-17 tonnes per hectare in humid regions with two to three crops annually. If best technical means are used to eliminate the yield-limiting factors, these yields could be obtained. Detailed analyses show that water in the semi-arid Sahel region is not the main limiting factor (de Wit, 1992; Bindraban et al., 1999). Poor soil fertility (nitrogen and phosphorus shortfalls at crucial times in the growing season) limits growth rate and yield. Field experiments have confirmed this (Breman et al., 2001). The potential yields for many crops are at least 5-10 times the actual yields.
McMillan and Masters (2003) use a different approach to illustrate similar possibilities for increasing yields by comparing actual yield of cereals in Sub-Saharan Africa to yields obtained in other regions. Actual cereal yields in Asia have increased from 1.5 tonnes per hectare in 1960 to over 3 tonnes per hectare in 2000, while in Sub-Saharan Africa they increased from 0.7 tonnes per hectare in 1960 to 1 tonne per hectare in 2000. Although this increase of 43 percent is considerable, the gaps in yield of Africa compared with other continents has widened considerably over the past four decades.
Gaps in yield (attainable actual and potential actual) within Africa are far greater than the gaps cited between Africa and the rest of the world. Various crops typical for Africa when grown outside the continent produce higher yields. Sorghum, millet, rice, wheat and maize all respond dramatically to improved technology. Hybrid sorghums achieve yields exceeding 6 tonnes per hectare and top yields of over 10 tonnes per hectare are reported (NRC, 1996). Hence, technology already 'on the shelf' has the potential to enhance land productivity in Africa once adapted and fine-tuned to location specific situations. In the following subsections, constraints and opportunities to improved productivity of various crops and animals will be discussed. The most important crops in the four priority systems are maize, rice, sorghum, millet, legumes, cassava, yams, cocoa and coffee; important animals are cattle and goats. Most farming systems in Africa are based on a multitude of crops, often in combination with animals. Here the mixed cropping is studied at field level in an attempt to understand its complexity at farm level. The disappointing productivity trends for land, labour and inputs suggest that available technologies are not eagerly adopted by farmers. It is important to discover whether 'on the shelf' technologies can enhance the productivity of the majority of the African farming systems, or whether they are inappropriate and need adaptation.
The trends described above reinforce the general observation made in Chapter 3 - yield increases in Africa per hectare have not kept track with population increases. Where there are improvements to farming systems, they tend to be very modest, but there are exceptions. Egypt with its irrigated agriculture has had productivity increases similar to other irrigated areas in the world. However, in the rainfed systems, yields are increasing but not in pace with population increase. There is no simple explanation: low soil fertility and therefore very modest attainable yields; complicated systems with no applicable fine-tuned technologies; and pests, diseases and weeds that are reducing already very low attainable yields. This all leads to a bleak picture. However the potentials for improvement may be there. The lack of information on the production ecology of the systems, however, does not allow a comprehensive production ecological analysis.