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close this bookSustaining the Future: Economic, Social, and Environmental Change in Sub-Saharan Africa (UNU, 1996, 365 pages)
close this folderPart 3: Environment and resource management
close this folderAgricultural development in the age of sustainability: Crop production
View the document(introductory text...)
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

Suggested approaches to sustainable production

Wisdom from farmers' production systems

Systems that have a high potential for sustainability mimic natural ecosystems and ensure continuity in supply of some important resources for plant growth, e.g. vegetation, nutrients, and water, and prevent their losses from soils by erosion. These systems are those practiced by farmers whose habitats scientists are trying to understand. Biological control is one of the benefits of maintaining the ecological diversity of plants and animals.

Therefore, approaches that incorporate farmers' relevant knowledge and experience into designs for improvement will most likely be sustainable, as has been shown in the examples of mimicking natural ecosystems. The Association of Farming Systems Research and Extension (Norman 1982; Okigbo 1989; Hildebrand 1990) emphasizes approaches requiring a thorough diagnosis of existing systems and conditions before designing any improvements and experimenting and testing them in farmers' fields. Improvements will definitely be necessary because the existing farmers' systems, developed in a given set of conditions (such as shifting cultivation at low population densities with bush path highways), break down when practiced in situations for which they are not meant.

Such improvements should gradually build up from existing systems (Hildebrand 1990) instead of replacing them completely. When replacement is the adopted approach, the system breaks down and frustration occurs, as was noted by Nye and Greenland (1960: v), who reviewed the effectiveness of technologies generated in Europe and applied in tropical Africa and observed that "after a quarter of a century of experiment in the African tropics, we have failed to introduce to the forest regions any method of staple food production superior to the system of natural fallowing used in shifting cultivation." The current research emphasis on multiple cropping, agro-forestry, including alley systems, and mulching of various kinds to produce plant cover for the soil represents a refinement of farmers' shifting cultivation to fit emerging situations.

Requirements of new technologies

To be sustainable, new technologies should address the whole farm and interactions in plant production systems (Hildebrand 1990). Donor interest in Farming Systems Research and Extension (FSR/E) may no longer be strong, as was shown by the funding problems of FSR/E and the complete absence of donors during a recent international meeting (AFSR/E annual meeting, East Lansing, Michigan, September 1992). Yet sustainability and FSR/E are compatible concepts because whole farm situations and interactions of their components need to be understood. An implication is that the days of neatly laid out field experiments with one or two factors and high environmental controls may be over (Federer, personal communication, 1991). High levels of variability are to be expected at farm level and more attention to interactions than to the main effects may pay off in understanding farmers' reel situations and problems.

Sub-Saharan Africa and water problems

At optimum water supply and disease and pest control, Linnemann and his co-workers (1979) showed that the potential annual grain production in Sub-Saharan Africa was about 10 billion metric tons. Burningh et al. (1975) estimated that the potential agricultural area in Africa in 1965-1973 was 23 per cent of Africa's total land area. Out of this area, only 6 per cent is cultivated, with a yield of 1,000 kg/ha, i.e. about 10 per cent of the 10,000 kg/ha potential. Burningh et al. (1975) concluded that the problem is one more of social and economic than of biophysical potential. Nevertheless, biophysical factors are of great importance if this potential is not exploited in a sustainable manner. Many of the improved crop varieties currently in use in Sub-Saharan Africa do not yield as much as they would if adequate water were available. In the humid zones of West and Central Africa, water distribution is such that crops are oversupplied for certain months of the year and undersupplied in others. A lack of water is also noted in some areas in the humid zone because of poor distribution, which often reduces the duration of crop growth (de Wit et al. 1979). Eastin et al. (1969) have shown that moisture stress adversely affects inflorescence development and grain filling and leads to inefficient use of nutrients. With stress, either fertilization is inhibited or grains that are already fertilized abort. Irrespective of breeders' expected yields, crop yields decline because of the reduced duration of growth attributed to the moisture stress of cereal grains (de Wit et al. 1979) or of roots and tubers (Lawson 1985). An urgent technical input is to ensure timely water distribution for plant growth. Even for cassava, which is tolerant of moisture stress, storage root yield is decreased during the dry season months of the transitional zone of West Africa (Lawson 1985).

Implications for plant breeding

For most plant breeders, favourable yields are based on high economic yields and the high harvest indices of improved varieties per unit of space and time. Varieties are usually evaluated in monocropping systems using the recommended levels of fertilizer and pest control. Evidence now available suggests that these values need to be reassessed in plant production systems aimed at sustainable development. To conserve soil resources, there is a need to conserve biological life: living organisms can be adversely affected by pesticides and other chemicals; ploughing accelerates soil and nutrient losses owing to erosion and leaching; good harvests at the expense of leaves, stems, and other plant parts may be detrimental because the additional vegetative materials needed for mulching the soil are lost. In highly vegetative plants, nutrients that could have been leached off or volatilized from soil may be held in plant parts and later released during decomposition.



Fig. 11.3 Effects on cassava root yields of insecticide protection applied to intercropped cowpeas in an IITA experiment in southern Nigeria, 1987/88 (Source: unpublished data from IITA Experimental Service)

The age of sustainability calls for a modification of breeding objectives. It may require new approaches in testing improved varieties and a re-examination of selection procedures. A trait lost may be hard to recover at later stages in a breeding cycle. An example is cassava, whose shoot and root yields may be reduced significantly by spraying cowpea intercropped with the cassava as compared with unsprayed cowpea and cassava (fig. 11.3). Without a systems approach, this interaction may be missed because cowpea protected from insect attack by spraying yielded higher than when unsprayed. Thus the limited objective of increasing cowpea yield is achieved but the broader objectives of ecological balance and of increasing total yield are not attained.

The lack of involvement of users in the development of technologies can lead to non-acceptance of the results. The success of intensive agricultural development in Taiwan is mainly the result of farmer pressure on researchers. In a study of 150 selected projects by US firms, Merrill-Sands (1992) reported a failure rate of about 67 per cent and a success rate of 15 per cent in cases where user influence on the products developed was characterized by hostility and distrust. The exact opposite, 67 per cent success and 14 per cent failure, was observed when client pressure or demand-pull led to product development. The high rate of cassava (TMS 30572) and sweet potato (TIB1) adoption in West Africa, particularly in Nigeria and Cameroon, respectively, appears to relate more to their development in unfertilized soil, which may have simulated the farmers' soil conditions, than to any other factor.

Virtually all the crops that generate export income, such as cocoa, coffee, and oil-palm, are declining in importance in the world market. For increased export earnings, Sub-Saharan Africa may need to produce specialized products in which it commands some advantages. The luxuriant vegetation, fruits, and nuts in African landscapes contain important oils, some protein, lubricants, and condiments (Okigbo 1980). Their potential benefits to Sub-Saharan Africa and in the world market remain unknown. For example, the cash income derived from some protected isolated stands of trees (Elaeis guineensis, Irvingia gabonensis, Raphia spp., and Bytyrospermum paraatoxum) in southern Nigeria in 1980 was at least 2.3 naira per tree per day or over 10 naira (US$0.5) at 1980 rates (Okafor 1980). Multiplication and improvement of important plants can be effected by biotechnology, which also has considerable potential in health care (medicine, nutrition) and in the chemical and cosmetic industries. New, improved crops with desirable characteristics, as well as cheap pest and disease control measures, are other potential benefits of biotechnology that Sub-Saharan Africa may miss out on if action is not taken to utilize existing facilities and create new ones if necessary.

Enhancing women's productivity

To attain sustainable development arising from the increased agricultural productivity of Sub-Saharan Africa, the human resource potentials of both men and women should be developed. Concrete efforts should be geared towards enhancing the productivity of all those involved in food crop production. As women are now responsible for the bulk of the food crops produced on small farm holdings, the emphasis should be on providing them with access to the resources and inputs necessary to increase their productive capacity (specific resources have already been discussed).