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close this bookSustaining the Future. Economic, Social, and Environmental Change in Sub-Saharan Africa (UNU, 1996, 365 p.)
close this folderPart 3: Environment and resource management
close this folderAgricultural development in the age of sustainability: Crop production
View the document(introduction...)
View the documentIntroduction
View the documentThe ecological zones of Sub-Saharan Africa
View the documentGeneral crop production constraints and potentials for overcoming them
View the documentTechnologies with potential for sustainable resource management
View the documentWomen's underexploited potential
View the documentSuggested approaches to sustainable production
View the documentSummary
View the documentConclusions
View the documentAcknowledgements
View the documentReferences

General crop production constraints and potentials for overcoming them


Paulino (1987) reports that cereals (wheat, maize, sorghum, millet, rice) constitute 54 per cent by calories of the food crops grown in Sub-Saharan Africa, while root and tuber crops (cassava, yams, potatoes, and taros) make up 27 per cent of calories. All other crops (plantains and bananas, grain legumes, fruits and vegetables, etc.) make up the balance of 19 per cent. Many traditional varieties of these crops are low yielding and the improved varieties released do not seem to have made an impact in the Sub-Saharan Africa region. De Bruijn and Fresco (1989) report relatively small increases in cassava yield (23 per cent) compared with maize (55 per cent) in developing countries during 1984-1986 compared with 1961-1965. The yield increases shown in figure 11.1 are small compared with the population increase, which stood at 71 per cent in Africa during the same period. The small increases in production and yield of cassava and maize during the two decades illustrate the small average effect of introducing improved crop varieties into Africa. Increases in other major crops such as yams, rice, wheat, sorghum, and millet were similarly low in comparison with human population increases. Sweet potato, which produces more dry matter per unit area and time than any other crop in Sub-Saharan Africa, is not a preferred crop, but, fed to pigs and poultry, it can be converted to protein and fats.

Fig. 11.1 Area, yield, und production of cassava and maize in Africa, 1961-1965, 1974-1976, and 1984-1986 (Source: adapted from de Bruijin and Fresco 1989)

Insufficient and excess rains, as well as management and socioeconomic factors, also result in reduced productivity. Across the ecological regions of Sub-Saharan Africa constraints are related to the amount and distribution of rains and to poor soil conditions for plant growth. Rainfall in Sub-Saharan Africa is highly variable, ranging from excessive in places such as Debunscha, Cameroon, with 10,000 mm average annual rainfall to about 200-300 mm in some areas of West Africa. Drought-induced crop losses in the drier areas of Sub-Saharan Africa occur frequently (Matron 1987). In the tropical zone, drought-induced crop losses may occur during years in which the rains are poorly distributed (Ter Kuile 1987; Lawson 1985). The incidence of diseases and pests is enhanced by rainfall and soil condition. An example is the noxious weed spear grass (Imperata cylindrica), which thrives in areas where forest vegetation is replaced by grass. Many diseases such as Pythium and Phizoctonium rots occur mainly in high-rainfall areas, as does cassava bacterial blight, Xanthomonas manihoti, which requires high humidity to survive (Lawson and Terry 1984), while the cassava mealybug (Phenacoccus manihoti MF) is very serious during dry seasons (Nwanze et al. 1977; Herren 1989). Multiple soil nutrient deficiencies, especially in areas with a high cropping intensity, low inherent soil fertility characterized by low cation exchange capacity (CEC), high acidity, rapid organic matter decomposition, high P fixation, high erodibility, and leaching -all compounded by a dominance of low activity clay (Kang and Juo 1981) - render most of the soils in Sub-Saharan Africa unsuitable for intensive crop production using available technologies.

Farmers with few resources, a large proportion of whom are women, dominate in Sub-Saharan Africa. They may manage efficiently at their resource level, which, unfortunately, is low in productivity. High resource inputs require more efficient and demanding managerial skills, which should be demonstrated by profit margins in competitive markets and not by ability to survive. Women who dominate in farming have very limited access to production resources.

Institutional and policy constraints have been discussed by Vallaeys et al. (1987), Olayide and Idachaba (1987), and other authors in Mellor et al. (1987). They emphasize the underdeveloped marketing and input/output infrastructure of the agricultural sector, low investment in research, amounting to about 0.5 per cent of gross agricultural product (Vallaeys et al. 1987), poor research-extension-farmer linkages, which reduce the effectiveness of technology transfer (Collinson 1987), and the high dependence of agricultural inputs on imports, which are becoming increasingly costly as foreign exchange becomes scarce. Yet the prices of farm outputs decline.

Potentials for overcoming constraints

In spite of the constraints enumerated above, crop production in SubSaharan Africa could increase tremendously if adequate human and institutional resources were available to manage the biophysical resources. To buttress this statement, Ruttan (1988) noted that the achievement of the level of development attained by developed countries will depend upon Africa's commitment to the investment in the institutional and physical infrastructure required to exploit the production potential of the resources with which Africa is endowed. De Wit et al. (1979) report a calculation by de Hoogh et al. (1976) that shows that, whereas the potential arable land in tropical Africa is 643 million ha, the area in use is only 174 million ha, or 27 per cent.

The same data indicate that yield expressed in 1965 grain equivalent for Africa was only 74,000 million out of a potential 9,474,000 million kilocalories, i.e. only 0.8 per cent. Thus the biophysical resources available in Sub-Saharan Africa and elsewhere in the world are grossly underutilized. Because these calculations were based upon biophysical potentials (fertilizer and water are not limiting, diseases and pests are controlled, optimal available solar radiation is captured), it was concluded that the main obstacles to increased crop production are socio-economic (capital, institutions, policy, culture). Sub-Saharan Africa could resolve its food deficit problem if even 25 per cent of this estimation were attained. How do we manage the resources of crop production (including human, with an emphasis on women farmers) so that resources are sustained? This question calls for a re-examination of the technologies available and their usefulness in sustained resource management.