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Part 3: Environment and resource management
Agricultural development in the age of
sustainability: Crop production
Agricultural development in the age of sustainability: Livestock production
The fuelwood/energy crisis in Sub-Saharan Africa
The case for mineral resources management and development in Sub-Saharan Africa
Agricultural development in the age of sustainability: Crop production
The ecological zones of Sub-Saharan Africa
General crop production constraints and potentials for overcoming them
Technologies with potential for sustainable resource management
Women's underexploited potential
Suggested approaches to sustainable production
Humphrey C. Ezumah and Nkoli N. Ezumah
It is estimated that by the year 2025 the population of Sub-Saharan Africa will double. A major concern is how to feed the population of over 480 million (without South Africa) whose 3 per cent rate of annual population increase is about the highest in the world. Climatic, ecological, and socio-economic problems plague Africa. Poor infrastructure for crop production, handling, and marketing, compounded by climatic extremes, causes fluctuations in food availability and subsequently hunger. About 100 million inhabitants of SubSaharan Africa (or 25 per cent) consume less than 80 per cent of the requirements recommended by the Food and Agriculture Organization of the United Nations (FAO), including the proportion filled by food imports (World Bank 1989). Because the food security of the majority of the Sub-Saharan African population that is dependent upon farming is directly influenced by agriculture, emphasis on agricultural productivity and related activities will most likely alleviate the food deficits of the most vulnerable sector. Production not only must increase but should be sustained in the long term.
The concern for sustainable development is reflected in the growing literature and policy initiatives on the issue. Definitions range from those that base sustainability on ecological balance to those that combine ecological with socio-economic concepts. Dover and Talbot (1987) view a sustainable production system as one whose productivity continues indefinitely with no noticeable degradation of the ecosystem. Earlier, Conway (1985) emphasized sustainability as the ability of a system to maintain its level of productivity in spite of a major disturbance such as is caused by an "intense or large perturbation." These definitions do not give the degree or level of production to be maintained and at what pressure on the environment. Thus the boundaries have not, according to Lynam and Herdt (1988), been ascertained in these definitions. In this paper, the explanation of sustainability that incorporates biophysical, socio-economic, and cultural concepts given by Okigbo (1989) is preferred. He defines a sustainable agricultural production system as "one which maintains an acceptable and increasing level of productivity that satisfies prevailing needs and is continuously adapted to meet the future needs for increasing the carrying capacity of the resource base and other worthwhile human needs" (1989: 3). Thus a production system leads to the development of people if it results in advancement from the current position. Development attains a sustainable level when its processes are controlled and perpetuated by resources within the reach of, and/or controlled by, the system such that any external influences do not upset the equilibrium attained. Highly developed people (or societies) attain a high quality of life using resources that they control or that are accessible to them to "own, maintain or hire" (Okigbo 1989).
The objective of this paper is to examine how agricultural development can be oriented to be highly productive and sustainable. Therefore the main discussion areas in this paper are:
· The ecological zones of Sub-Saharan Africa: their major crops and production constraints.
· General crop production constraints and the potential for over coming them.
· Technologies with potential for sustained resource management.
· Women's underexploited potential.
· Approaches to sustainable crop production in Sub-Saharan Africa.
The ecological zones of Sub-Saharan Africa
Sub-Saharan Africa has over 23 million km2 of land with a potential arable area estimated at 643 million hectares and forest at 700 million hectares, which is being cleared at the rate of 3.7 million hectares per year (World Bank 1989). Only 174 million hectares of the land are currently under cultivation. Sub-Saharan Africa is demarcated into five major ecological zones, which are determined mainly by rainfall and relief (table 11.1).
The humid forests of West and Central Africa
In the humid forests of West and Central Africa, tree crops such as oil-palm (Elaeis guineensis), cocoa (Theobroma cacao), rubber (Hevea braziliensis), and protected economic woody plants are grown in plantations or in multistorey associations with root and tuber crops. Rice is a major crop in both swamps and upland areas in the humid forest zone. Compound land (land immediately adjacent to the compound or homestead, often in permanent cultivation) is particularly important in these areas. Household refuse, including ash and plant and animal wastes, is used to maintain a stable multistorey plant production system. Protected trees, perennial herbaceous plants, including plantains and bananas, together with raffia are mixed with vegetables, spices, yams, and some maize in farms around the homesteads. The trees gradually decrease in number or completely disappear from farms as the distance from homesteads increases.
Soil fertility and structural instability are the most important plant production constraints of this zone. Luxurious forest growth soon gives way to eroded land when clearing is followed by intensive cropping (Kang and Juo 1981; Lal 1989). Soil acidity is common, and weeds, which flourish in the heavy rains, compete with tree and other food crops. Another important effect of forest clearing is loss of plant genetic diversity, exposure of soil to wind and water erosion, and the extinction of useful plant resources (Okigbo 1989). This resource waste is further accentuated by high average human (63 persons/km2 in West Africa and 10/km2 in Central Africa) and animal population pressure, intensive farming, overgrazing, construction development, hunting, and burning. A reduction in maize yield in this zone owing to cloudy skies and reduced insolation has been observed (IITA 1983).
The Southern Guinea Savanna and Derived Savanna
The humid forest of the Southern Guinea Savanna, sometimes called the sub-humid zone of West Africa, has been mostly cleared and cropped for a long period and has been overtaken mainly by grasses and shrubs. At an early stage of succession from forest to savanna is the Derived Savanna, which is better known as Guinea Savanna (Ter Kuile 1987). Rainfall in the Derived Savanna may be slightly higher than that in the Southern Guinea Savanna (table 11.1). Sorghum and maize are important cereals, and root crops (cassava and yams) grow and yield highly.
Table 11.1 Major eco-zones and characteristics in Sub-Saharan Africa
|Zone||Number of humid months||Mean annual rainfall||Growing period (days)||Main soils|
|1. Forest: coastal West some Africa and Central Africa||7-9 +||1400-4000 + (mostly unimodal)||270-365||Mostly acidic (ultisols and oxisols); non-acid (inceptisols, entisols, verti sols, alfisols, etc.)|
|2a. Derived Savanna||6-7||1300-1500 (bimodal, some areas)||240-270||Moderately leached soils (alfisols, some ultisols, etc.)|
|2b. Southern Guinea Savanna||5-6||1200-1500 (partially bimodal)||190-240||Mainly alfisols and related soils; acidic ultisols and oxisols in some wetter areas; also entisols and vertisols in some areas|
|3. Northern Guinea Savanna||4-5||880-1300 (unimodal)||140-200||As above, with greater proportion of non-acid alfisols|
|4. Sudan Savanna 2 4||500-880||90-140 (unimodal)||Alfisols and some drier aridisols, etc.|
|5a. Eastern and southern African highlands||7-12||750-1000 (unimodal)||270-365||Ultisols, oxisols, vertisols|
|5b. Eastern and southern African highlands||5-6||750-1000 (bimodal)||190 240||Alfisols, ultisols. oxisols|
Source: Adapted from Papadakis (1966); FAO (1978); Kowal and Kassam (1978); Lawson (1979).
The high infestation of tse-tse fly debars the use of oxen as sources of power; therefore labour at peak growing seasons is a major constraint. This zone is poorly served by roads and marketing systems. Weeds, particularly the parasitic Striga, attack the dominant cereal crops. The soils are relatively rich and are structurally more stable than humid forest soils but are frequently deficient in some major nutrients, whose efficiency may be reduced by negative interaction with minor elements, e.g. phosphorus (P) and zinc (Zn).
The Northern Guinea Savanna
The Northern Guinea Savanna of West Africa, also called the sorghum-millet belt of West Africa, receives lower rainfall than the southern part. It is excellent for maize growth and some of the highest yields in West Africa are obtained from this zone (IITA 1984). Sorghum is also important. However, drought at critical stages of maize development frequently reduces grain yields. High soil temperatures and high evaporation rates are also important constraints (Hullugale 1989). The parasitic weed Striga attacks cereals and grain legumes (cowpea), the two important food-crop groups grown in the Northern Guinea Savanna. The soil is more favourable for cropping and responds to N, P, and S applications. Soil erosion caused by wind and soil crusting and capping has also been reported (Charreau 1970).
The Sudan Savanna
The Sudan Savanna is located to the north of the Northern Guinea Savanna. Rainfall is unimodal, its duration is uncertain, and crop failures are common. Millet and cowpeas are the major food crops in this area. Cereals are grown on about 70 per cent of the total cultivated area of the Sudan Savanna (Matron 1987). Cotton and groundnuts are the major commercial crops and are sometimes grown for export.
The eastern and southern African highlands
The generalizations about the preceding zones are modified by high elevation in Rwanda, eastern Zaire, Burundi, and the mountainous plains of eastern Africa. The monsoon tropical climate and the high incidence of radiation result in extremely high productivity.
In the area of the eastern and southern highlands where rainfall is unimodal, high maize yields are recorded. However, rainfall may limit production. Banana is an important staple and groundnuts are also grown commercially. Coffee and tea, particularly the former, are export crops.
In the area where rainfall is bimodal (March/April to May and November to January), the short duration of the rainfall requires very intensive labour in land preparation and planting, the consequences of which are frequent crop losses. The crops grown are maize, coffee, and bananas. High population pressure on the soils of both highlands, with only 5-7 months of rainfall, causes low productivity. Soil loss is high, particularly in the communal lands of Zimbabwe, where it is reported at 50 tons/ha/yr (Whitlow 1987) and results in reduced yields of crops (Collinson 1987).
There are, therefore, three broad zones: (a) the humid forest zones of West and Central Africa, (b) the savanna zone, demarcated by the level of available rainfall, and (c) the highlands, including plateaux.
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.
Technologies with potential for sustainable resource management
Good technologies with missing links
In Sub-Saharan Africa, considerable efforts have been expended on the development of improved cereals, root and tuber crops, and food and fodder legumes by plant breeders, and also on the characterization and identification of the limitations of the soils. Pest control measures have also received attention, particularly from international (IITA, IRRI, ICRISAT, WARDA, ILCA, ICP),1 national, and other research centres and universities in Africa. Agronomists and soil scientists have conducted a lot of research on responses to fertilizer application of various crops in different ecological settings, and breeders and disease and pest control specialists have documented results based on chemical, host plant resistance, biological, and chemical control measures.
Each of these results, introduced into a farmer's system, provides some relief to problems. The ephemeral nature of some of the relief is realized when the breeders' variety yields less than expected in the intensive multistorey crop association system of small-scale farmers (duo and Ezumah 1992), and when the expected response to fertilizer is not realized, either because the increased crop pressure requires higher applications (Wahua 1983; Olasantan 1992), or because the soil physical conditions have deteriorated so much that the effectiveness of fertilizer is reduced in intensive systems (Lal and Greenland 1978). Similarly, the undesirable long-term effects of pest and disease control by a non-integrated approach have been documented (Maxwell 1990). A holistic approach to research and extension, which also incorporates the concepts of integrated pest management (IPM), could reduce the dangers of unsustainable crop production in SubSaharan Africa.
Technical innovation in agriculture is generally not designed so as to exploit the complementary and synergistic effects of the important results for sustained crop production enumerated earlier. Such complementarities are achievable when technologies are developed from current farmers' knowledge base, using multidisciplinary experiences (Norman 1982; Hildebrand 1990). The central thesis is that resourcepoor farmers do not adopt technologies that require costly inputs of labour, cash, and materials or technologies for which inputs are not readily available. These technologies therefore do not fit in the farmers' production environment and frequently break the linkages that enhance resource conservation.
The International Institute of Tropical Agriculture, for example, developed an early maturing erect cowpea that, together with other improved varieties, required frequent applications of insecticide. Among the early varieties were TVX3236 and IT82E-60. As long as chemicals were subsidized when the Nigerian currency, the naira, was relatively strong, some farmers, particularly those on larger farms, grew these cowpea varieties. The majority of the small-scale farmers did not adopt the early, erect types because (a) they required insecticides that were not available or that they could not afford and (b) the vegetation required as animal feed was too scanty. Thus the improved variety that matured early enough in the low-rainfall zones did not satisfy the conditions for its adoption (Carr 1989). With respect to fertilizers, recommendations are available in virtually every country in Sub-Saharan Africa. The limited use of fertilizers, even when prices are subsidized, is attributed to poor distribution systems (Harrison 1987). Although many farmers in south-eastern Nigeria (Unamma et al. 1985) and in Zaire (Osiname et al. 1987) are aware of the importance of fertilizers and herbicides, most are not making use of them because (i) they may not be available either at all or when required, (ii) they are too costly, or (iii) they require equipment that the farmers do not own, e.g. knapsack sprayers. A common feature of the technologies cited - which also include tractorized tillage, liming, short-stalked, high-yielding sorghum for farmers who
may require stalks for fencing or for fuelwood, and zero tillage unaccompanied by a weed control package for reduced tillage systems - is that they do not fit into farmers' production environments because some components that would facilitate their usefulness in existing systems are missing. Adoption of the early cowpea and of dwarf sorghum might, because of high yields, lead to a destruction of vegetation from other environments for animal feed and for fuelwood. It is also noted that the modern practices of conventional agriculture, which comprise land clearing and preparation (tillage systems), fertilization, weed control, and harvesting, have elements of environmental degradation.
Mimicking natural ecosystems
Almost all the sustainable systems currently available in Sub-Saharan Africa mimic natural ecosystems. These systems comprise traditional shifting cultivation, which is sustainable at low population pressures, well-managed multiple-cropping systems (which include compound land systems), the alley cropping system, and the fadama or inland valley systems. These systems may have some or all of the following attributes: extending the duration of growth of the plant community, increasing light-capturing potential through multi-layer interception over a longer period, and recycling nutrients from deep layers. The systems also integrate many groups of plant species - ephemerals, annuals, and perennials - in the same land area. By mimicking nature, microclimates suitable for the growth of many species of plants, and that therefore enhance diversity, are created (Okigbo and Greenland 1976; Juo and Ezumah 1992). Multiple-cropping (i.e. intercropping and rotation) leads to more efficient resource use and this is reflected in yield advantages (Osiru and Willey 1972; Okigbo and Greenland 1976; Willey 1979; Ezumah and Lawson 1984, 1990). Associations that exhibit yield advantage may be long-duration plants intercropped with short-duration plants (Okigbo and Greenland 1976; H. Ezumah 1990) or combinations of short-duration crops belonging to the same family, e.g. sorghum and millet (Willey 1979), or of different species, e.g. sorghum and pigeon pea (Rao and Willey 1983) or maize and cowpea (Ezumah and Ikeorgu 1993). Other advantages of multiple-cropping include improved physical and chemical soil conditions for growth (Lal 1976), reduced soil temperature (Lal 1976; Ikeorgu and Ezumah 1991), reduced soil surface evaporation, and increased water content (Lal 1976). Increased biological activity in the soil (e.g. earthworm activity) in intercropping compared with monocrop rotations (Hullugale and Ezumah 1991) and a reduction in surface runoff and soil loss and therefore a reduction of soil degradation have also been reported for intercropped situations (Aina et al. 1977). In Ouagadougou, Hullugale (1989) showed that undersowing Stylosanthes with maize reduced soil temperature and increased soil moisture, which was significantly improved by conserving moisture through the erection of cross ridges or tying of ridges. Ikeorgu and Ezumah's (1991) results also showed reduced soil temperature in cassava intercropped in four complex mixtures with maize, okra, and egusi melon compared with sole cassava or cassava + maize intercrops. These results highlight the need to focus research on farmers' current systems and to improve on them. They also show the importance of conserving plants and animals in the wild, because their usefulness to humans, apart from the broad concept of ecological balance, is unknown.
Some of the advantages of multiple cropping are also obtained by surface mulching of the soil with dead material (Lal 1976). Okigbo (1977) studied a wide range of mulching materials including gravel, sawdust from wood, translucent white and black plastics, as well as foliage and twigs from different plant sources including leguminous and non-leguminous plants. The short-term advantages of mulching on an alfisol in Nigeria appear to relate more to improvement of the soil microclimate for plant growth than to chemical properties, because higher crop yields were obtained from the plastic mulches than from the foliages and the twigs. These effects do not, however, negate the long-term benefits of mulching (Lal 1989). A major difficulty of mulching is the procurement of materials. Lawson and Lal (1980) estimated a threshold of 4-6 tons/ha for effective mulching on an alfisol in Nigeria. This quantity of mulch is too much for a lowresource farmer to carry. Akobundu (1980) reported higher maize yield without N fertilization over a five-year period of continuous cropping in association with living legume plants (Psophocarpus palustris and Centrosema pubescens). Little response to N fertilizer was observed in the legume-associated plots compared with the control, which responded to over 60 kg N fertilization per hectare. For greater benefits, a well-established legume plot is required (Mulongoy and Akobundu 1985). Cassava intercropped with maize generates enough mulch to sustain yields. The IITA (1985) reported stable yields of cassava and maize over four years on an alfisol in southern Nigeria. Longer-duration maize (over 120 days to maturity) with high dry matter gave higher yields than shorter-duration maize (less than 100 days to maturity). The short-duration maize allowed in more light to the associated cassava in their intercrop system.
The most recent innovation in mimicking the natural ecosystem is the alley cropping system (Kang and Wilson 1987). In alley cropping, the multistorey association of the compound land setting is rearranged so that trees occupy adjacent hedges (hedgerows), about 4m apart. Crops are then grown in the alleys between the hedges. Trees are chosen for certain characteristics such as deep rooting (to recycle nutrients), ability to coppice and to produce high biomass (which is pruned for mulching and nutrient release), and, sometimes, rhizobia N-fixing ability. Legume trees in the hedges contribute N in excess of 40 kg/ha to associated crops (Kang 1988). Even non-legumes recycle deeply located nutrients at about 13-19 kg/ha. Although the alley system contributes to moisture conservation, organic residue, and structural and chemical improvements to the soil, a reduction in the yields of associated crops owing to reduced light because of the tree canopy has been observed (Lawson and Kang 1990). Considering its soil improvement features and the stability of alley cropping over a period of years (Kang and Wilson 1987; IITA 1989: fig. 2), alley cropping is a sustainable system that needs refining. Unlike compound farming, it is amenable to large-scale methods. The labour requirements for pruning, which often coincides with other important farm activities (e.g. weeding and harvesting of maize and melon), are a serious setback (Ngambeki 1985). Alley species suitable for acid soils are still being sought. Figure 11.2a shows a rapid decline of maize yields in a continuous cropping system, even if fertilizer is applied. Alley cropping can stabilize maize yields at levels that vary with inputs, e.g. fertilizer (fig. 11.2b). In the latter case, fertilizer augments biologically generated nutrients to sustain maize yields.
Fig. 11.2 Muize production at IITA, Ibadan. (a) Relationship between length of continuous cultivation and maize yields. (b) Sustainability of maize production in alley cropping systems (Source: Kang and Wilson 1987)
Inland valleys or fadamas, though small individually, total tens of millions of hectares in West and Central Africa. International Institute of Tropical Agriculture estimates for West Africa alone gave about 14 million ha (IITA 1980). Inland valleys are well watered and have enormous potential for producing food, especially rice. In China, inland valleys have been cropped continuously for centuries (duo and Lowe 1986). The neglect of Sub-Saharan Africa's inland valleys, according to the International Institute of Tropical Agriculture (IITA 1990), is attributed to lack of knowledge about their management, which leads to their infection by vectors of many harmful diseases, such as Schistosomiasis, river blindness, malaria, and guinea worms. In addition to water availability, the inland valleys are sustainable and give higher rice yields because they are relatively high in fertility as a result of inflows of nutrients from the uplands. Increased fertility of the inland valleys of Sub-Saharan Africa can be attained by rotating rice with legumes tolerant of water logging, some of which are Crotolaria spp., soybean (Glycine max), and Sesbania spp. Thus, exploitation of the potential for sustainable plant production in the inland valleys of Sub-Saharan Africa requires more research.
Disease and pest control
Some known crop management methods to control diseases and pests include chemical and mechanical measures. These may require high capital and labour inputs. Host plant resistance and biological control measures, though requiring high initial investment at institutional levels, are sustainable and indirectly affordable by the low-resource farmers of Sub-Saharan Africa. Recent examples include the control of cassava bacterial blight (Xanthomonas manihotis) by resistance breeding (Hahn et al. 1979) and the effective reduction of the cassava mealybug pest (Phenacoccus manihoti Mat-Fer) by biological control (Neuenschwander and Hammond 1987). A parasitoid, Epidinocarsis lopezi, introduced from Latin America and released at strategic sites has contributed to the reduction of the cassava mealybug epidemic in Africa.
Many examples of disease and pest resistance through breeding have been documented for various crops in Sub-Saharan Africa. Claims that diseases and pests (except for weeds, for which it has been demonstrated) are controlled by intercropping need further research because reports have been inconsistent (IITA 1978; Francis 1989).
Women's underexploited potential
One of the causes of the "weak agricultural growth" in Africa is the underutilization of human resource potential (World Bank 1989: 2). This is particularly manifested in the gender gap in access to production resources. The majority of African food crop producers who are smallholder farmers, and women in particular, experience great difficulties in increasing production. To achieve sustainable agricultural production it is imperative to eliminate those factors that hinder the productivity of the majority of food producers.
African women are responsible for about 70 per cent of the labour input in food production. Their activities include hoeing, planting, weeding, transportation of crops and planting materials, food processing, and storage. Men, on the other hand, have been largely responsible for bush clearing, land preparation, staking of crops, and hunting (FAO 1982). Recent trends characterizing gender roles in African agriculture have been identified (Guyer 1986: 396-398), namely, that male tasks in agriculture are declining owing to: (a) the decrease in forest cover and game resources; (b) the greater participation of men in out-migration; and (c) male predominance in export crop production. As a corollary, women's agricultural work has been intensified. Factors responsible for this development are that: (a) shorter fallows are now used, resulting in increased weeding; (b) as the distance of farms from homes increases, there is greater demand for the transport of crops and planting materials; (c) as the food trade increases, the demand for food processing increases; and (d) the predominance of men in migration leads to an increased workload for women in food production.
Despite the increased responsibility of African women for food production, their productive capacity is deteriorating because they continue to suffer from less access to production resources and inputs, agricultural innovations, and extension services. Some specific constraints that are important for women farmers in Sub-Saharan Africa concern limited or no access to resources such as land, capital/credit, labour, and agricultural innovations.
Access to land
In most African societies women traditionally had use rights to land (Pale 1976). The introduction of the Western concept of private land ownership has been to the detriment of women (Boserup 1970). Some development programmes in Africa have also exacerbated women's restricted access to land. Pankhurst and Jacobs (1988) report women's loss of land through land reforms in Zimbabwe. The marginalization of women in the allocation of irrigated rice fields to men in the Gambia adversely affected rice production and gender relations and also culminated in the failure of the project (Dey 1981; Carney 1988).
Access to credit
Smallholder farmers, particularly women, who lack access to credit experience great difficulties in purchasing inputs to increase their production. Access to credit is often based on ownership of collaterals such as land or membership of cooperatives and farmers' associations, which many African rural women lack (Loutfi 1980; Cloud 1985). Consequently, most agricultural bank loans in the past went to "absentee" or "progressive" farmers (professionals, top bureaucrats, and military personnel) (Bukh 1979; D'Silva and Raza 1983; Okuneye 1984).
Access to labour
The male predominance in rural-urban migration for wage employment has resulted in the intensification of women's work in agriculture and in labour shortages in food production, particularly in female-headed households (Rogers 1980). Women's lack of access to credit has a concomitant effect on their ability to purchase paid labour (Roberts 1988). A greater number of women consequently dissipate a lot of energy that could be channelled towards increased productivity on their farms in other enterprises such as working as paid labour on other people's farms or providing exchange labour in return for labour received (Guyer 1984; N. Ezumah 1990). Women's cultural obligation to provide labour on their husband's farm also results in limitations on the amount of time they can devote to their own farms (Babalola and Dennis 1988).
Access to improved technologies
The dissemination of information about innovations in agriculture as well as access to training, fertilizers and other inputs, and extension services have been geared mainly to male farmers with adverse effects on women's productivity. Most training in agriculture has been directed to men. The marginalization of women in terms of access to production inputs has often resulted in the deterioration of women's productive capacity (Muntemba 1982). "Progressive" farmers, usually men, have received preferential allocation of extension visits and services (D'Silva and Raza 1983; Okuneye 1984). Some of the adverse consequences of this neglect of women's role in the implementation of agricultural innovations include a loss in adaptive efficiency when women's operational knowledge is not taken into consideration and lower adaptation rates owing to women's lack of access to technology and training (Kumar 1988: 142).
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