Traditional Cowpea in Senegal, a Case Study.
Anthony E. HALL
1- Importance of Cowpea in Senegal
1-1: Socio-geographical description
Cowpea (Vigna unguiculata [L.] Walp.) is the most important food legume grown in the tropical Savanna zones of Africa. Although indigenous to southeastern Africa, cowpea has spread worldwide and is extensively cultivated and consumed in regions of Asia, South and Central America, the Caribbean, the United States, the Middle East and southern Europe. Cowpea is a preferred staple food in many regions of Africa. Its desirability reflects the fact that the leaves, immature pods, fresh seeds (southernpeas or “green pods”), and dry grain can be eaten or marketed. Also, some varieties have a short cycle and mature early and thus are able to provide food during the “hungry period”–the period at the end of the wet season when food can become extremely scarce in semi-arid regions of Sub-Saharan Africa. The dry grain is also commonly milled and consumed in numerous traditional main dishes of Africa as porridge and breads, fed to young children as weaning foods, and eaten as processed snack foods. Cowpea grains, as well as the vegetative parts, make major nutritional contributions to diets. The mature grain contain 23-25% protein, 50-67% starch, B vitamins such as folic acid which is important in preventing birth defects, and essential micronutrients such as iron, calcium, and zinc. Although a significant amount of cowpea is commercialized, it plays a critical subsistence role in the diets of many households in Africa, Latin America and Asia, providing nutrients that are deficient in cereals. An added advantage of cowpea is that the plants can be harvested as fodder for livestock. In certain regions of West and Central Africa the fodder (haulms) is highly valued. During the height of the dry season stored cowpea fodder becomes an important feed for livestock.
From an agronomic perspective, cowpea is well suited to the agro-climatic-edaphic, technological and socioeconomic situations in Sub-Saharan Africa. The traits that distinguish cowpea from many other crops currently grown in Africa include: (1) substantial adaptation to drought; (2) high potential to biologically fix nitrogen in marginal soils with low organic matter (<0.2%), high sand content (>85%), and a broad range of pH (4.5-9.0); (3) tolerance to high temperatures during the vegetative stage; (4) tolerance to shade; (5) rapid vegetative growth; and (6) tri-purpose utilization, producing vegetable leaves and pods, dry grain and forage. The adaptation to drought is especially important for the dry Sahelian and other Savanna zones of western and eastern Africa. Cowpea production, because of its high adaptability to drought-prone conditions, relative to other crops, is the crop of choice in these harsh environments. For example, the ‘Agricultural Research Institute of Senegal’ (ISRA) recommends cowpea for production in the northern part of the country where soils are sandy, water holding capacity is low, and rainfall is substantially less than in the southern part of the country. Groundnut is the recommended legume crop for the higher rainfall areas in the center-south and southern regions of Senegal.
Total worldwide production of cowpea is estimated at 3.3 million tons (FAO, 2001) of dry grain of which 64% is produced in Africa. Conservative estimates suggest that greater than 12.5 million ha are planted annually to cowpea around the world. Of this area, about 9.8 million ha are planted in West Africa, making it the region with the largest production and consumption of cowpea in the world (CGIAR, 2001). The primary cowpea-producing countries in West Africa are Nigeria, Niger, Mali, Senegal, Burkina Faso and Ghana. Significant production also occurs in the East African countries of Uganda, Mozambique, Tanzania, and to an increasing extent, Ethiopia. Average world yield of cowpea grain is quite low at less than 0.3 tons/ha. Within Africa, average cowpea yields vary dramatically from 0.05 to 0.55 t/ha depending upon the varieties planted, the extent of cultural inputs (e.g., fertilizer and pesticides), the cropping system (intercropping versus sole cropping) and the agro-climatic-edaphic conditions.
Cowpea production area in Senegal was estimated as being 90,685 ha in the 2001 growing season. However, the planted area has considerably varied since 1980 (Table 1). The northern regions of Louga and St Louis constitute the largest area of cowpea production with about 65 % of the total. The center-north regions of Diourbel and Thies represent the second most important zone, with about 29 % of the planted area. Cowpeas are mainly grown in the semiarid Sahelian region of Senegal. The Sahel (Figure 1) is a band of land on the southern fringe of the Sahara desert and is a semiarid transition region between the desert and the wetter Savanna zones. It stretches across Africa from the Atlantic Ocean and northern Senegal in the west to the Sudan in the east. It has a short rainy season during July, August and September followed by a long dry season that becomes very hot with strong winds and blowing sand in May and June. Since 1968 there have been several years of severe drought in all Sahelian countries. Rainfall data from northern Senegal (Table 1) describe some of these droughts. For the fifty years before 1968, average annual rainfall in Louga had been 442 mm. Traditional systems of agriculture that had evolved over many years were adapted to these conditions and adequately productive in most years. In an average year the rainfall provided enough water for local varieties of the drought-resistant annual crops that were grown, pearl millet (Pennisetum glaucum), sorghum (Sorghum bicolor), cowpea and peanut (Arachis hypogea), which in Senegal had a cycle from sowing to harvest of 70 to 90 days. In 1968 the annual rainfall was only 212 mm and the pearl millet, sorghum, cowpea and peanut crops failed to produce much grain and food for the people, and mainly provided a small amount of forage for the livestock. In 1969 the rains returned providing abundant water with 599 mm at Louga. But since 1969 there have been 29 years of a virtually continuous drought in the Sahel with an average annual rainfall at Louga of only 276 mm. Even the southern wetter boundary of the Sahelian zone at Bambey in the Diourbel region had an average rainfall of only 466 mm from 1968 through 1998, compared with an average rainfall for the forty-seven years prior to 1968 of 670 mm. In only one of these dry years (1989), did the rainfall at Louga exceed the long-term average of 442 mm and in 23 of the 29 years the rainfall was less than 300 mm. These droughts caused changes to occur in the traditional systems for producing cowpea and the other crop species, and agronomic research was conducted to overcome the severe problems caused by the droughts.
Figure 1. Rainfall of Senegal.
1-2: Role of cowpea in food security
In the traditional system, harvests of near-mature green pods
of early traditional cowpea varieties started in September. When
shelled, these pods produce what is known in the United States as
fresh southern peas, which after boiling are an excellent food.
In Senegal, these near-mature pods usually are boiled whole after
which the consumer has to shell them while eating them. The importance
of the availability of green pods of cowpea in September was that
they provided food during a time of year when it can be in short
supply. Also, sale of green pods provided an opportunity for farmers
to obtain cash. Harvesting of traditional food crops in northern
Senegal, such as pearl millet, sorghum, peanut, and dry grain of
late varieties of cowpea typically occurs in October to December.
Consequently, if previous crops were not very productive and granaries
are nearly empty, there is a tendency for local food supplies to
be depleted by August and September; this is called the “Hungry
Period”. Since 1985 with the introduction of cowpea varieties CB5
(Bingen et al. 1988) and subsequently Melakh (Cisse et al, 1997),
which are earlier than the landraces, considerable quantities of
cowpea have been consumed as green pods during August and September
(as much as 30% of the crop). Sometimes green pods have been the
only food that was available to rural families in northern Senegal
during the “Hungry Period”. Cash from the sale of green pods also
has been important because it can be used to buy other staple foods
such as pearl millet or imported rice. Fresh “green pod” cowpeas
and dry cowpeas often are cooked with a cereal, such as pearl millet
or rice. When one part cowpea (on a dry weight basis) is combined
with three parts of the cereal, they make a food with a near-complete
and balanced set of nutrients. Cowpea provides much of the protein
and vitamins such as folic acid, and significant carbohydrate. The
cereal provides most of the carbohydrate (and thus food energy)
and protein with essential amino acids that complement those present
in the protein of the cowpea. Harvesting and sale of green pods
are, done by women in most cases (Figure 2). Green pods can have
a price that is about double that of dry cowpea grain on a per pea
basis. Consequently, sale of green pods can be very lucrative for
farmers living close to highways that provide opportunities for
making sales to travelers. Some of the vendors shell pods while
they are waiting for buyers and put the shelled peas in plastic
bags, but this product does not keep as well as intact green pods.
The early flowering varieties CB5 and Melakh are better suited for
the production of green pods during the “Hungry Period” than the
traditional landraces because the highest prices are received for
green pods that are marketed early in the second decade of August.
Green pods have now become a popular food in some cities in Senegal.
By using different varieties that begin flowering at different times,
farmers can market fresh green pods and farm families can consume
them over a period of several weeks during and after the “Hungry
Figure 2. Women, selling cowpea green pods along the highway.
2- Traditional and Improved Cowpea Cultivation
2-1: Traditional cultivation and related local knowledge
Cowpea is a warm-season crop that has been grown in Senegal for centuries (Ng and Marechal, 1985). Sene (1966) hypothesized that medium-cycle cowpea landraces had been introduced from Nigeria for flood-water recession cultivation in the north of Senegal next to the Senegal river, and that some longer-cycle landraces may have been introduced from Mali for intercropping with pearl millet in the wetter regions of Senegal. Dispersion to the rest of the country took place through trade and migration. Germplasm collection done between 1953 and 1960 resulted in 74 accessions being obtained by ISRA (Sene, 1966). Subsequent work to eliminate redundancy reduced the number to 61. However, by 2002 the number of accessions available at the Bambey research station reached 247 mainly through introductions from other countries of West Africa. Germplasm collection in Senegal mainly was done in the major cowpea production areas (regions of Louga, St Louis, Thies and Diourbel) with only a few visits being made to the center-south, eastern and southern zones. For the conditions of Bambey (14 o 42’ N, 16 o 28’ W), the collection has been classified into two distinct groups: short-day cowpeas that are extremely sensitive to photoperiod (day length), and a group that is either insensitive or only slightly sensitive to day length with respective to the initiation of flowering.
Short-day cowpeas initiate floral buds when day length plus twilight becomes less than 12.5 hours, which corresponds to the period between mid-September and the end of March in Senegal. When sown at the beginning of the rainy season in July, varieties in this group produce much forage but little grain, since they begin flowering late in September after producing abundant forage. When planting date of these short-day varieties is delayed until mid-August, such as is practiced in relay intercropping, excessive vegetative growth and competition with pearl millet is avoided. In the relay intercropping system, significant cowpea grain can be produced by November to December, which is during the beginning of the dry season, providing the rainy season has provided sufficient reserves of moisture in the soil profile. The other group of cowpea varieties that is relatively insensitive to day length for their flowering is the most useful group for green pod and dry grain production in the Sahelian zone, especially if they have a relatively short period from sowing to first flowering. Except for Ndout and Baye Ngange, the traditional cowpea varieties discussed below are relatively insensitive to day length.
Traditionally varieties have been named based on: grain color or grain size (Figure 3), pod size, cycle length, or a person’s name (such as an introducer, important personality or a woman if the landrace is highly productive).
Landraces similar to the variety 58-57 were extensively cultivated in the northern area prior to 1968 and the area of production of these landraces progressively expanded south due to the droughts during the 1970’s and 1980’s. 58-57 is a landrace that was selected by D. Sene in the late 1950’s and when grown at the Bambey research station under optimal conditions it matures about 75 days after planting. It is drought resistant, which made it the variety of choice during the period of droughts since 1968 but it was not effective when the rainy season was very short. Originally, it was collected at Podor where it was being grown on the edges of the Senegal River in the flood-water recession or “decrue” system. It has a spreading plant habit and is dual purpose in that in addition to grain it can produce substantial hay. The hay is an effective feed for livestock in the dry season. The seed size is however relatively small with a 100-seed weight of approximately 12 g, and a cream color with dark brown eye (Sene 1966).
Many other landraces used in the flood-recession system are known under the generic name ‘Matam’. They are generally photosensitive and have a spreading plant habit. The grain is usually small to medium with 100-seed weights varying between 10 and 18 g. The grain color is generally cream with a dark brown or black eye.
Landrace Mame Penda, also called Ndiaga Aw, Dankha, Patate or Tomate, became popular in the north and center-north regions by 2000. This landrace has large brown seed (100-seed weight of 21 g) that can be sold at a premium price all year long. Mame Penda matures in about 75 days from sowing under optimal conditions, has a spreading habit and is dual purpose in that it can produce substantial grain and hay. The name ‘Tomate’ originated from the brown color of the grain, which economizes in tomato-paste usage with rice-based dishes. The name ‘Patate’ may be related to the large grain size that resembles, in miniature, a sweet potato tuber.
Landrace Mame Fama is widely grown in the northern zone and has moderate-sized white seed with a 100-seed weight of 14 g and a black eye (Sene, 1966). Of particular importance is the fact that Mame Fame is slightly earlier than the previous landraces. Mame Fama reaches maturity about 70 days from sowing under optimal conditions compared with 75 days for Mame Penda and 58-57. This difference in cycle length of only 5 days enables Mame Fama to more effectively escape late-season droughts and produce earlier green pods than either 58-57 or Mame Penda. However, due to its shorter cycle length, Mame Fama produces significantly less hay than either 58-57 or Mame Penda.
Ndout, which is very photoperiod sensitive, and Baye Ngagne, which is moderately sensitive to photoperiod but earlier than Ndout have large seed with a 100-grain weight of 18 g with grey-blue speckles and a cream-colored background (Sene, 1966). Prior to 1968 they were extensively grown in the wetter Savanna zone in the central regions of Thies and Diourbel as relay intercrops with pearl millet. For relay intercropping, Ndout and Baye Ngagne are sown into pearl millet fields in mid-August and, if there has been sufficient rain to charge the soil profile, produce a modest quantity of grain by mid-November to early December. The rainy season in the central region typically ends in October and in the many dry years since 1968 the soil profile has not been charged sufficiently and relay intercrops have produced little cowpea grain. The area of cowpea sown to relay intercrops of Ndout and Baye Ngagne decreased substantially since the mid 1970’s.
Figure 3. Grains of cowpea landraces differing in color and size.
2-1-2: Cropping Systems
Cowpea is cultivated in Senegal using essentially three systems: Sole cropping and relay intercropping during the rainy season; and the flood-water recession system during the dry season.
While most cowpea production in Africa involves the uses of intercropping of cowpea with other crop species, as of 2002 virtually all of the production in the Sahelian zone of Senegal was by sole crops of cowpea, pearl millet, and peanut. In the northern and center-north areas short (70 day) to medium-cycle (75 day) traditional landraces and shorter-cycle 64- to 68-day varieties developed by ISRA (Institute of Agricultural Research, Senegal) were being grown in annual rotation with pearl millet and peanut. In most cases, the extensive sandy soil areas have been prepared for sowing at the beginning of the rainy season by manual or animal-draft harrowing. These soils are so deficient in nitrogen and phosphate that, except for the years with extremely low rainfall, grain yield of pearl millet has been limited more by the small supplies of these plant nutrients in the soil than by the drought. In contrast, cowpea is less dependent on these nutrients than the cereal crops. Cowpea has a symbiotic association with Rhizobia bacteria in the soil, which results in fixation of atmospheric nitrogen, and it has enhanced uptake of phosphate from the soil solution due to effective associations with fungi that colonize roots causing them to be mycorrhizal. Cowpea can fix as much as 200 kg/ha of atmospheric nitrogen, which is enough to supply the needs of a productive crop of cowpea and leave some in the soil for the following cereal crop. The enhanced uptake of phosphate due to the associations with fungi can make cowpea more effective than some other crop species at obtaining phosphate from infertile soil that have low levels of available phosphate. Traditionally no organic or mineral fertilizers have been applied to fields of cowpea. The annual rotations practiced with sole-crops have the advantage that the limited supplies of fertilizer and manure that are available can be applied to the pearl millet, which has greater needs for nitrogen and is more responsive to fertilizer and manure than cowpea or peanut. Pearl millet grown the year following a cowpea crop will benefit from the improved soil nutrient conditions resulting from the rhizobial and fungal associations with the root system of the cowpea. Also, prior crops of one species can have additional beneficial effects on another crop species grown on the same land the following year. For example, pearl millet can suppress the fungus responsible for the ashy stem blight disease of cowpea, and prior crops of cowpea can cause suicidal germination of the seeds of the parasitic weed striga (Striga hermonthica) that attacks pearl millet or sorghum but not cowpea.
Sowing and Weeding
Sole-crop cowpea usually has been sown at the beginning of the rainy season as soon as the soil is wet enough to establish the crop. It has substantial drought resistance during the vegetative stage but needs adequate supplies of water during flowering and early pod development. Early sowing also may enable the crop to escape the late-season droughts that often occur. Since 1968, however, sowing often has occurred in late July to early August in the northern and center-north areas. In these conditions only varieties with a very short cycle, such as Mame Fama and those recently developed by ISRA (Cisse et al. 1995, 1997) have been able to escape the late-season drought in most years. Sowing often was done by hand with two or three seeds per planting hole and without thinning. Wide spacing was practiced, sometimes with 1 to 2 meters between individual plants in both directions. Cowpea can be most productive if it is sown during a short period of time just after the first major rainstorm. A substantial area of cowpea and peanut must be sown during this short period. When the supply of cowpea seed or labor is limiting, the most effective method for hand planting is to use a spreading variety and place seed at a spacing of about 1 meter by 1 meter. About two weeks after the cowpeas emerge, weeds are traditionally controlled with a push hoe to prevent them from either growing tall and shading the cowpeas or depleting soil moisture and nutrients. This weeding is repeated about two weeks later. Common landraces are susceptible to the parasitic weed Striga gesnerioides (Figure 4) that attacks cowpea but not cereals (pearl millet or sorghum) or peanut.
Several insect pests can substantially reduce cowpea yield and productivity. At the beginning of the growing season the major insect pest is hairy caterpillar [(Amsacta moloneyi), Figure 5]. The occurrence of hairy caterpillar is sporadic but it can be devastating in the drier part of the cowpea production zone such as in the Louga and St Louis regions. A single wave of hairy caterpillar can completely destroy fields of cowpea seedlings by eating their leaves. If the wave of hairy caterpillars is late, the cowpea plants may have sufficient vigor and leaf production to out-grow and survive the attack. None of the common landraces of cowpea is resistant to hairy caterpillar. Early planting at wide spacing of vigorous spreading varieties, as practiced by farmers, slightly aids survival of the crop. These cowpea cultivars are able to resume their development after a partial defoliation by hairy caterpillars because of their spreading growth habit. However, all of the cowpea varieties grown in Senegal, as of 2002, can be totally destroyed by an early attack of hairy caterpillar.
Cowpea aphids [(Aphis craccivora), Figure 6] can cause problems at any time in the growing season but are most damaging when they infest seedlings during dry weather. These small black shiny aphids feed on the phloem and are particularly damaging to young growing points causing plants to be stunted. They also transmit viral mosaic diseases. The landraces have little genetic resistance to cowpea aphid, and farmers rely on natural biological control, rainstorms to wash off the insects and enhance fungal parasitism of the insects, and the capacity of these varieties to resume plant development after the attack because of their indeterminate growth habit. These measures are not very effective if there is a pronounced infestation of cowpea aphid.
In the wetter part of the cowpea zone (south of Diourbel) the
most damaging insect pest is the flower thrip (Megalurothrips sjostedti).
These are small thin shiny black insects that are most readily observed
inside flowers (Figure 7). They can however cause substantial damage
before flowers, are produced by feeding on floral buds. Traditionally,
relay intercropping is practiced in this zone where cowpea is planted
late (mid-August) into pearl millet. With late planting, photoperiod-sensitive
cowpea varieties begin flowering in October, which is after the
flower thrip population has subsided, and this can be an effective
measure for at least partially escaping damage from this pest. Flower
thrips also can cause some damage to cowpeas grown in the center-north
area around Diourbel and Thies. The landraces grown as sole crops
in this area have little resistance to flower thrips.
Figure 4: Parasitic weed striga attached to cowpea roots.
Figure 5: Feeding larva of hairy caterpillar.
Figure 6: Cowpea aphids on cowpea pods.
Figure 7: Flower thrips and damage on cowpea flowers. (Courtesy of C. Fatokun. At IITA)
The major disease problems of cowpea in the center-north and northern areas of Senegal result from infection with two seed-borne organisms: bacterial blight (Xanthomonas campestris pv vignicola) and cowpea aphid-borne mosaic virus. These diseases can substantially reduce yield and since the pathogens are seed-borne the diseases can become widely distributed.
Bacterial blight (Figure 8) is transmitted from infected seedlings to adjacent plants by rain drops and causes chlorotic patches (orange with a yellow halo) and necrotic patches on the leaves. The pathogen also can cause cracking and cankers on the stem and peduncles. The disease is endemic to the semiarid Sahelian zone. Landraces Mame Penda and 58-57 are resistant to bacterial blight.
Cowpea aphid-borne mosaic virus (Figure 9) is transmitted by cowpea aphids and causes distortion and mottling of the leaves and can stunt the plants. The most effective control measure is to use varieties with resistance to major biotypes of the cowpea aphid-borne mosaic virus, unfortunately most landraces, including Baye Ngagne, Mame Penda, and 58-57, are susceptible to major biotypes of this viral disease. The use of pathogen-free seeds that were obtained from disease-free plants can provide a control measure that is partially effective when fields are not subjected to an early aphid attack with the potential to transmit the virus but certified, pathogen-free cowpea seed usually was not available to farmers in Senegal as of 2002.
Charcoal rot or ashy stem blight disease [(Macrophomina phaseolina), Figure 10] can cause substantial damage to cowpea when soils became dry and hot. The extent of this disease has increased in the Louga region due to some mono-cropping of cowpea during the past thirty years. The mono-cropping, in which cowpea was planted year after year on the same field, was a response to the droughts, since it was the only crop species capable of producing significant food during this period in most years. None of the landraces or varieties of cowpea available in Senegal has been shown to have any resistance to this disease.
In wet conditions Choanephora species can infect green pods at the point where petals remain attached to young pods resulting in a wet pod rot (Figure 11). The problem mainly occurs in wet locations and seasons, and with varieties, such as the introduced variety CB5, that flower very early and thus are useful for green pod production in the “hungry period”.
When pods become dry and crisp they become susceptible to rain damage, which causes mold to proliferate in the pod walls and grains. The introduced variety CB5 has thin papery pod walls and is very susceptible to this type of dry pod rot. Landraces have tougher pods that resist dry pod rot and their later maturity does not coincide with main rainfall period. Another solution to this problem is to harvest pods as soon as they are crisp, dry them further under the sun, and then thresh the pods and put the grains in a place where they will not be damaged by rain.
Figure 8: Leaf symptoms of bacterial blight.
Figure 9: Cowpea aphid-borne mosaic virus symptoms.
Figure 10: Cowpea killed by ashy stem blight disease.
Figure 11: Wet pod rot caused by Choanephora species.
Pods should be harvested as soon as they become crisp. Pods usually are harvested by hand, without pulling up the plant, to provide additional opportunities for the plant to produce pods. Spreading varieties sequentially produce pods and harvesting can be conducted over several weeks. Pods are usually dried in the sun to facilitate threshing and winnowing, which also are done manually. Dry pods are subsequently protected against rain, to avoid the development of dry pod rots that can totally destroy the grain.
Cowpea storage weevil or bruchid (Callosobruchus maculatus) eats cowpea grain making distinctive round holes (Figure 12). Damage is apparent about 2 to 3 months after harvest and virtually all of the grain may have holes by 6 months. Consumers have a strong aversion to grain that has been damaged by weevils, but it still can be effective as seed, although, germination percentage may have been reduced.
Protective methods are used if grain is to be stored longer than 2 months. Infestations start in the field on pods but population growth accelerates following threshing, when eggs are laid directly on the seeds. The eggs hatch and the larvae bore into the grains and complete their development within them. Adults emerge from the grain through the characteristic round exit holes made by the larvae. The adults live 5-10 days during which they mate. Each female lay about 50 eggs that she glues to the cowpea grains, and then the cycle begins again. An individual life-cycle is completed in 3 to 4 weeks. Consequently, from a modest initial infestation many of the grains may have either weevil eggs on them or holes within them after two months in storage and two cycles of weevil reproduction.
There are several traditional methods of protection that are available at the farm level. They included several preventive methods. Regular and early harvesting of mature cowpea pods to minimize the initial infestation. Separation of damaged from healthy pods and grains during storage. Storage of cowpea grain in well-sealed, and carefully cleaned granaries. In addition grains are often mixed with botanicals (leaves, fruits or bark) of several plants, such as the neem tree (Azadirachta indica). Cowpea grain has been stored in clay pots with small mouths, such as those used for holding water, with a layer of ash or sand to prevent entry of bruchids. This method is partially effective for storing a small amount of cowpea grain for use as seed the following year. In general, none of other methods is very effective and this encouraged people to consume or sell most of their cowpea grain within two months of harvest.
For relay intercropping photoperiod-sensitive varieties of cowpea, such as Ndout, or Baye Ngagne, were sown into pearl millet fields about one to one and half months prior to the cereal harvest. Therefore the cowpea sowing date was between mid-August and early September. A low sowing density was used which varied between 5000 to 7500 plants per hectare (Tardieu et al., 1966). Relay intercropping took advantage of late rainfall plus any residual water left in the soil after the pearl millet crop. This cowpea crop required few inputs and benefited from the weed control practiced for the pearl millet. Cowpea plant development and flowering occurred essentially after the pearl millet harvest. After this harvest the pearl millet straws were aligned along the cowpea rows (Figure 13), which reduced soil-water evaporation and soil-temperature fluctuations and may have enhanced nodule formation by rhizobia. Cowpea produced pods that matured in November and December, when there was no competition from the cereal.
Prior to 1968, relay intercropping with pearl millet was the main method for growing cowpea in the center-north area around Bambey and Thies. Field studies showed that a minimum of 200 mm of residual water after millet, in the first 150 cm soil depth, would satisfy the need of relay-intercropped cowpea and result in a potential yield of 1000 kg/ha. Similarly cowpeas with residual soil water of 125 to 200 mm would potentially yield 500 – 800 kg/ha. With between 100 and 125 mm, 200 – 400 kg/ha can be obtained from cowpea with relay intercropping. With less than 100 mm of residual soil water after pearl millet, relay intercropping becomes hazardous. Hydrologic balances were simulated for Bambey using information on rainfall, evaporative demand, and soil water-holding and crop characteristics. It was found that between 1923 and 1967, residual soil water after pearl millet was greater than 200 mm in three years, 125 –200 mm in 19 years, and 100 – 125 in 8 years. Thus 67 % the time, relay intercropping of cowpea could have been successful in the period prior to 1968.
Surveys have shown that up to 200-300 kg/ha of cowpea grain can be obtained with relay intercropping in farm conditions, without diminishing the pearl millet yield compared to its sole-crop performance. However in most years since 1968, there has been insufficient rain for relay-intercropped cowpeas in the areas around Bambey and Thies. In 8 years out of 10, between 1968 and 1977, the residual soil water after the pearl millet crop was less than 100 mm in the first 150 cm soil depth (Dancette, 1981). In the center-north area the relay intercropping system and Ndout-type varieties have failed to produce grains in most years (70 % of the time) since 1968. Consequently, the photo - insensitive varieties, such as 58-57, with a growth cycle of about 75 days and sole-cropping have moved south and replaced much of the relay intercropping in the center-north area around Diourbel and Thies.
Figure 12: Cowpea grains damaged by bruchids.
Figure 13: Pearl millet straws between cowpea plants in relay intercropping
Flood-water recession system
The flood-water recession or ‘decrue’ system is practiced along the edges of the Senegal River. In this system, seed is sown as the flood water recedes and the plants grow on stored soil moisture during the cool and dry season from November to April. The Matam-type landraces that are photosensitive and have a spreading plant habit are generally used in this system. Landraces of the 58-57-type that are insensitive to photoperiod also have been grown in the ‘decrue’ system.
Several crop species are cultivated when the flood-water recedes. The acreage annually available for this system varies considerably between 10,000 ha in years of severe drought to 150,000 ha depending on the extent of the flooding. About 85 % of this area is dedicated to sorghum. Cowpea is the second most important crop cultivated in the ‘decrue’ system, followed by corn, watermelon, tomatoes and sweet potatoes (Laricollais et al., 1984). The flood occurs in the Senegal River valley from July to October after which it recedes. This recession lasts until December to January. The amount of water stored in the soil largely determines the yields of the ‘decrue’ crops. The climate of the dry season in the river area is characterized by short days and night temperatures that can be as low as about 10o C.
A minimum of one month of flooding is required for a field to be effective for the ‘decrue’ system. When water recedes after the flood the soil begins to dry out. Weeds rapidly emerge and farmers controlled them through cultivation either before or after planting. It is estimated that 50 % of farmers controlled weeds before planting, and the rest planted their crop into weedy fields. Planting was done, by hoeing the soil to provide a place where a hole would be made for seed placement. Two or three seeds were placed in each hole, which was subsequently covered with wet sand. Plant densities were generally low at about 5000 plants / ha. Young plants emerged in a couple of days and were exposed to attacks by birds and insect pests. There should be several cultivations during crop growth to control weeds. Mature pods are harvested in March – April. Grain yields have varied between 100 –300 kg / ha. The product arrives in markets at a time when the main-season grains are rare or have deteriorated due to bruchid attacks. Thus cowpea grains from the flood-water recession system can often be sold for premium prices.
In rural areas
Surveys made in the Louga and St Louis regions during the late 1980’s to early 90’s (Hamdy, 1989) indicated that about 60 % of producers ate their entire harvest. The crop of 30 % of the farmers was partly eaten on the farm and partly sold, and only 2.8 % of the farmers sold all of their grains. About 5 % of the sampled farmers indicated that some of their cowpea grain was distributed in bartering deals or for donations. It was estimated that per capita annual consumption was about 7.2 kg in these rural areas. Many villagers believe that cowpeas are good for their health and growth. Slightly more than 50 % also believed that cowpea caused digestion problems and discomfort due to flatulence. However, 74 % did not think that their knowledge influenced whether they did or did not consume cowpea. Thus per capita consumption appears to be mainly influenced by cowpea availability.
Couscous from cowpea flour has been prepared by about 50 to 60 % of villagers in the northern regions. Daxin was the second largest form of cowpea consumption in Louga at 28 % of the sample, while in the St Louis region it was prepared by only 6 % of the population. Daxin is a dish prepared from broken rice and is normally served with fish or meat, which is replaced in this case with cowpea. In these northern regions several other cowpea dishes were described, which reflect the familiarity of the people with different cowpea foods. Akara, a deep–fat fried snack food made from cowpea flour, was prepared by only about 3 % of the population. Presumably, this is because the concept of “snack food” is not widely spread in rural areas.
In urban areas
The majority of people sampled in Dakar and its suburbs (61.6 %) were completely familiar with cowpea while 38 % knew a little about it (Hamdy, 1989). Only 0.4 %, were not familiar with cowpeas. Only 20 % of the population did not eat cowpea. Yearly consumption per capita was estimated at 1.2 kg. This is less than one-fifth of the per capita cowpea consumption in the regions of Louga and St Louis. Availability of grain to consumers plays an important part in this difference since apprehension of flatulence was more pronounced in the rural regions than in Dakar and its suburbs. Another important reason for the difference in the per capita consumption of cowpeas is the lower market price in Louga region (60 to 100 CFA /kg during October to December) compared with 125 to 175 CFA/kg in markets in Dakar (1 Euro = 656 CFA in 2002). Households in Dakar mainly bought cowpeas during the “main season” which lasts from October to January. Only about 1 % of the population bought cowpeas during the period from February to September. Market price of cowpea relative to other staples such as peanuts, rice and pearl millet may be the major reason for the short sales period. During the “main season” market prices per kg in Dakar ranged from 125 – 175 CFA for cowpea while peanuts sold for 100 – 120 CFA, maize for 100 CFA, processed rice (imported) for 200 CFA and processed pearl millet for 150 CFA. Price differences between cowpea and the other staples, become greater during the February to September period. The cowpea price often increases to about 450 CFA/kg while the price of rice remains at 200 CFA/kg; peanut increases to 250 CFA/kg and pearl millet increases to 200 CFA/kg. Consumers tend to prefer the least costly food for their families regardless of nutritional differences in the foods. It should be clearly recognized, however, that cowpeas main role in the diet should be as a protein that is cheaper than either meat or fish, such as in the preparation of Daxin, and not as a replacement for rice or pearl millet as a source of food energy.
Another reason for the lack of demand for cowpeas during the “February to September” season is the poor quality because of bruchid infestation. Merchants often do not protect cowpea grain from bruchid infestations so during this period the grain in many cases is badly infested and this dissuades consumers from buying large quantities. Cowpea consumption was not necessary linked to income. Low income families (12 %) with less than 10,000 CFA per month as well as high-income families (15 %) with more than 100,000 CFA per month consumed cowpea.
The most popular preparations use cowpea in sauces that complement cereal dishes particularly rice. This preparation does not require more than a handful of cowpea grain, which often is from Ndout-type varieties. Cowpea grain in couscous and Daxin preparations are considered as side dishes or complements to cereals such as rice or pearl millet. Main dishes of cowpea such as Ndambe or ragout (stew) are also prepared by about 10 % of the population. Several other locally know dishes (Lakhou thiakhane, Thialal) were also reported. The snack food “Akara” is not the predominant form of consumption, but 60 % of the population, eat it on a regular basis.
In the main cowpea production zone in the northern and center-north areas, the following varieties have been recommended during the 1980’s and 1990’s: 58-57, Ndiambour, Mougne, Bambey 21, CB5, Mouride and Melakh. Each of these varieties has specific characteristics that make them useful in specific areas of the main production zone and specific environmental conditions.
Cowpea improvement started in the early 1960’s, with the identification of adapted and high performing landraces such as the small-seeded 58-57 (Sene 1966). The variety Ndiambour was bred using 58-57 and a parent that has larger grain size than 58-57, it has a 100-seed weight of 16g compared with 12g for 58-57 (Sene and N’diaye 1974). Ndiambour also is spreading and matures about 75 days after planting under optimal conditions. Ndiambour and 58-57 have some drought resistance and wide adaptation, and they have been recommended for cultivation in the northern and center-north areas. However, because of its smaller hay production than 58-57, Ndiambour was not widely adopted. The landrace Mame Fama with a lower potential yield of both hay and grain maintained itself in the northern zone because it reaches maturity 5 days earlier and probably is more reliable than 58-57 when the growing season is very short. The varieties 58-57 and Ndiambour are resistant to bacterial blight, but are susceptible to cowpea aphid-borne mosaic virus, the parasitic weed striga and several insect pests including: hairy caterpillar, cowpea aphids, flower thrips and bruchids.
Mougne was bred using the photosensitive landrace Ndout as a parent (Sene and N’diaye 1974). It was recognized that a photo-insensitive, spreading 75-day type variety was needed for solecropping that had the grain qualities of Ndout, which was very popular. Mougne has white grain with grey speckles and a 100-seed weight of 15g. Mougne was recommended for sole-crop cultivation in the more favorable center-north zone of the peanut basin. Mougne has resistance to bacterial blight but is susceptible to cowpea aphid-borne mosaic virus, striga and the insect pests: cowpea aphid, hairy caterpillar, flower thrip and bruchids.
Bambey 21 was the first very early (62-day) cowpea variety bred and released in Senegal (Sene and N’daye 1974). It also was the first variety released in Senegal that has an erect growth habit and does not produce much hay. Bambey 21 is the only known variety in the world that has an all-white grain color and it has a 100-seed weight of 17g. Bambey 21 could be very useful for producing flour by milling of whole grain. Bambey 21 has been recommended for use in the northern part of the cowpea zone.
CB5 (California Blackeye 5) was introduced to Senegal in 1985 in a famine relief program, following 3 years of extremely poor harvests due to severe droughts (Bingen et al. 1988). This variety had been tested previously, and had shown some adaptation to the drier conditions of Louga region due to its very short cycle length from planting to maturity (60 days). However it was not recommended for the center-north area because it could be seriously, damaged by cowpea aphids and diseases such as bacterial blight and the wet and dry pod rots that result from wetter conditions. A total of 650 tons of CB5 seeds was introduced to Senegal in June 1985 because local seed stocks of peanut and cowpea were very low and substantial seed only was available with this cowpea variety. In 1985, farmers planted CB5 but also their household seed stocks of local landraces of cowpea, thereby preserving a diverse set of cowpea germplasm. A system of advisors was put in place and some insecticides and methods of applying them were provided. The rainfall was low in 1985 (208 mm in Louga and 398 mm in Bambey) but well-distributed during the growing season providing good conditions for CB5. The area of cowpea was estimated to be 128,000 hectares, which is double the average value for the previous 25 years (Table 1). The average grain yield of cowpea in Senegal was 543 kg/ha, and in the northern peanut basin it was 726 kg/ha, which is also more than double that of the previous 25 years. Overall production of dry cowpea grain in 1985 was estimated to be 70,000 tons compared with an average annual production of 18,000 tons over the past quarter century with the greatest increases occurring in the Louga region. Not surprisingly, with this large increase in national production there were some major problems with marketing the surplus. Export of cowpea grain to neighboring countries was initiated but could not accommodate the surplus. Large stocks of cowpea were built up for use as food or seed, but some of it was not stored with effective methods and was destroyed by weevils. In 1986, there was a reduced level of financing and only modest support was provided to promote cowpea production. No cowpea seed was imported, some of the seed distributed had poor quality due particularly to infestation with bruchids and diseases such as bacterial blight and various dry pod rots. However, the area planted and yield per hectare of cowpea were still much greater than in years prior to 1985, and national production of cowpea grain in 1986 was 55,000 tons (Table 1). In subsequent years, until the second major cowpea program with the varieties Mouride and Melakh in 1993, national cowpea was small due to drought, insect pests, diseases, and shortages of seed, and the area sown to CB5 progressively decreased.
The overall conclusions are that the CB5 program was very successful for famine relief but not very effective for long-term development in that the effects were not sustainable. This variety was too sensitive to bacterial blight, cowpea aphid and the wet and dry pod rots. Major beneficial long-term consequences of the CB5 program were the realization that earlier shorter-cycle varieties could enable cowpea to become a major crop in the Sahelian zone of Senegal, and the extension of the “green pod” industry over a longer period and a much larger area.
Mouride was bred for use as a dry grain type of cultivar in the Sahelian zone. It was derived from a cross between ‘58-57' and a line developed by IITA, ‘IT81D-1137'. Mouride has resistance to cowpea weevil, cowpea aphid-borne mosaic virus and bacterial blight. During the on-farm tests, it was discovered that Mouride also has some resistance to the parasitic weed Striga gesnerioides (Willd.) Vatke. The partial resistance was confirmed by tests over several years in nurseries in fields heavily infested with Striga. It was shown that ‘IT81D-1137' has some resistance to race 2 of Striga occurring in Senegal, whereas ‘58-57' does not have resistance to this biotype. The Striga resistance of Mouride is not as broadly effective against a range of the Striga biotypes in Senegal as that of cowpea line ‘B301'. In the multilocation yield trials in Senegal, Mouride has consistently produced 18% more grain but 17% less hay than landrace ‘58-57' and much greater average grain yield than other traditional cultivars.
Mouride is semierect and begins flowering about 37 days after sowing and reaches physiological maturity under well-watered conditions about 68 days after sowing. It is one the most robust of the cultivars recently developed for the Sahel. Under well-watered experiment station conditions at Bambey, Senegal, Mouride has achieved grain yields as high as 3000 kg/ha, which is higher than has been achieved by any of the landraces or varieties that have been tested. Mouride also has greater resistance to midseason drought but less resistance to terminal droughts than Melakh, which has a slightly earlier flowering and shorter cycle length.
The seed of Mouride is cream with a brown eye and has a 100-seed weight of 16g. The grain are considered smaller than is desirable by some consumers, but the local landrace, 58-57, has even smaller seed (a 100-seed weight of 12g), and yet it has been widely used as a cultivar in northern Sénégal. The ITA (Food Technology Institute) in Dakar, Senegal evaluated the grain quality of Mouride and presented the results in an unpublished report in 1990. Protein content of Mouride based on total nitrogen measurements was 23% on a dry weight basis compared with 22% for CB5 and 25% for Bambey 21. Cooking time of Mouride was 44 minutes compared with 25 minutes for CB5 and 41 minutes for Bambey 21. In appearance during cooking, Mouride rated the lowest due to it having a high % of split grain, whereas Bambey 21 rated the highest due to it having firm texture and no split grain with CB5 having a good intermediate rating. In sensory evaluations, consumers rated Bambey 21' as being the highest with Mouride being the lowest due to perceived problems with texture and color, whereas CB5 was given a good intermediate ranking. The overall conclusion was that Mouride had acceptable but marginal grain quality that was not as good as the grain quality of either CB5 or Bambey 21. It should be noted, however, that from the early 1990's to 2002, neither CB5 nor Bambey 21 were being widely grown in Senegal due to weaknesses such as susceptibility to various diseases.
Mouride was released by ISRA for use in Senegal in 1992 (Cisse et al., 1995). In the growing season of 1993, World Vision International distributed seeds of Mouride to about 1000 farmers in 300 villages in northern Senegal. On-farm grain yields of Mouride in sole crops, were estimated to be about 1000 kg/ha by World Vision International. Mouride also was released for use in Guinea-Bissau in 1993. In a five-year Inter-CRSP (Collaborative Research Support Project) project that was funded by USAID that ended in February 2001, World Vision International evaluated and extended Mouride in several countries in West Africa including Ghana, Niger and Chad. In Niger, Mouride produced high grain yields and was very popular, with farmers requesting large-scale multiplication of seed.
Melakh was bred for use as a dual-purpose dry grain / green pod type of cultivar in the Sahelian zone. It was derived from a cross between an ISRA breeding line, ‘IS86-292', and an IITA breeding line, ‘IT83S-742-13'. Line ‘IS86-292' is from the same cross that produced Mouride. Melakh has resistance to cowpea aphid; cowpea aphid-borne mosaic and bacterial blight and partial resistance to flower thrips. It is a very early cowpea cultivar in that it flowers within about 35 days from sowing and reaches physiological maturity within about 64 days from sowing under well-watered conditions. It is semi-erect with strong resistance to terminal drought but can be damaged by midseason drought. The seeds have moderate size with a 100-seed weight of 19g and are white with a brown eye. In multi-location yield trials in Senegal, Melakh produced 30% more grain and forage than other early cowpea cultivars, such as CB5 and Bambey 21.
In the summer of 1993, seeds of Melakh were pre-released and distributed to about 1000 farmers in 300 villages in northern Senegal by World Vision International. On-farm grain yields in sole crops of Melakh were estimated, to be about 1000 kg/ha by World Vision International. Melakh was released by ISRA for use in Senegal in 1996 (Cisse et al., 1997). In subsequent years, World Vision International and the Belgian NGO, Aquadev extended Melakh in northern Senegal. More recently, World Vision International has been organizing farmer-based cowpea seed production cooperatives that are affiliated with the national union of personnel involved in seed production in Senegal (UNIS). An Austrian NGO, EWA, has been working with farmers in Senegal with the objectives of increasing production of Melakh, building cowpea storage facilities, and promoting cowpea export to neighboring countries. In addition to its use as a dry grain, Melakh has become popular in Senegal as a source of fresh green pods during the period of famine between mid-August to mid-September, which is prior to the harvest of the staple cereals, pearl millet and sorghum, and the main crop of cowpea as dry grain. Under the Inter-CRSP project, World Vision International also evaluated and extended Melakh in Ghana, Niger and Chad. Melakh produced high yields in Ghana and Niger and was very popular, with farmers in Niger.
Mouride and Melakh are complementary in that Mouride has higher yield potential and stronger resistance to mid-season drought, whereas Melakh has greater resistance to terminal drought. Both cultivars have resistance to the seed-borne diseases bacterial blight and cowpea aphid-borne mosaic virus. Mouride has partial resistance to cowpea weevil and Striga, whereas Melakh has resistance to cowpea aphid and partial resistance to flower thrip, which is a major insect pest. Since the types of drought and attacks by pests and diseases can vary from year to year, and among fields, farmers are encouraged to grow both cultivars as a means for increasing the stability of their farming systems. The cultivars could be grown as sole crops or as varietal intercrops. Varietal intercrops consisting of alternating rows of early erect and later flowering spreading cowpea cultivars were shown to produce more grain and hay and be more stable under dry Sahelian conditions than the best sole crops (Thiaw et al., 1993). The varietal intercrops or sole crops of cowpea would be grown in annual rotation with pearl millet and peanut.
2-2-2: Cropping systems
Much of the improvements have concerned the sole-cropping system. Research on plant spacing and geometry for relay intercropping has not influenced the practice. Some innovations have been introduced in the flood-water recession system.
In most cases land is prepared for sowing at the beginning of the rainy season by manual or animal-draft harrowing. Much of the soil in the center-north area can develop high bulk densities. From a theoretical standpoint, it would be advantageous to plow the land at the beginning of the rainy season because this results in stronger root growth and higher yield of cowpea, pearl millet and peanut. However, most farmers do not have the plows, draft animals or tractors to enable them to plow the land in sufficient time, at the beginning of the season, so they also can plant early. An alternative approach would be to plow the land just after the harvest at the end of the rainy season, but this only is effective if there is sufficient moisture in the soil. Where crop residues or manure are available, they would be most effective in improving soil fertility and structure if they are incorporated, by plowing. Useful production of cowpea can be achieved, however, if plowing is not possible and only harrowing is used to prepare the land.
One thousand kg of dry cowpea grain contain the equivalent of 50 kg of nitrogen (N), 17 kg of phosphate (P2O5) and 45 kg of potassium oxide (K2O). The whole plant including seed, foliage and roots could contain double these amounts. All the cowpea needs for nitrogen could be met by nitrogen fixation; unfortunately this process only begins to become effective about three weeks after planting. Consequently, in soils, which are very infertile ISRA has recommended that an application of 9 kg N/ha be made just prior to planting. Cowpea roots also form mycorrhizal associations with soil fungi. These associations also take about three weeks to become established and a pre-sowing application of 30 kg P2O5 /ha and 15 kg K2O /ha has been recommended by ISRA for infertile soils. A commercial fertilizer is available in Senegal with N: P2O5: K2O of 6-20-10. The amount of this fertilizer that has been recommended for cowpea grown in infertile soil is 150 kg/ha. The fertilizer should be applied just before sowing and should be incorporated to a depth of at least 10 cm by harrowing. Farmers typically have limited supplies of fertilizer, however, and in this situation it may be most effective from a system standpoint to apply the fertilizer to the pearl millet crop.
Cowpea is mainly sown into wet soil at the beginning of the rainy season, after a rain of at least 15 mm. Since 1968, sowing often has occurred in July in the northern and center-north areas. Cowpea should be sown as soon as the soil is wet enough to establish the crop because it has substantial drought resistance during the vegetative stage but needs substantial supplies of water during early flowering and early pod development. Early sowing enables the crop to escape the late-season droughts that often have occurred. Sowing is done either by hand with two or three seeds per planting hole or, preferably, with a peanut seeder having a disk with 8 holes of a size that will deliver one or two cowpea seeds per hole. The use of horse-drawn planters permits the sowing of cowpea seed in rows. This has provided the additional benefit that weeding also can be done using horse-drawn cultivators further reducing the bottleneck imposed by shortages of hand labor. For maximum yields, row spacing of 50 cm is recommended with 50 cm between planting holes for the more spreading varieties: 58-57, Mougne, Ndiambour and the landraces; and 25 cm between plants for the more erect varieties: Bambey 21, CB5 and Melakh. The 8-hole disk is a compromise that delivers seed every 33 cm. The amount of seed required is about 10 to 20 kg/ha depending upon the spacing and the variety. Plant emergence and survival can be enhanced if a chemical seed treatment is used.
About two weeks after cowpeas emerge any weeds are controlled with an animal-draft cultivator or by hand. This weeding should be repeated about two weeks later. Weeding is most effective if it is followed by dry weather, which facilitates the death of the weeds. If the parasitic weed Striga gesnerioides is present in the fields the only effective control method is to use the resistant variety Mouride. ISRA has recommended that emerged striga plants be pulled up by hand together with their roots, and that this be done prior to flowering to prevent dissemination of striga seeds, but this is not widely practiced and is not very effective in controlling striga. During the 1980’s and 1990’s there was an increasing tendency to sow cowpea seed using horse-draft seeders that had been used to plant peanut. Distance between rows of cowpea was about 50 cm as it often is for peanut and animal-draft cultivation has been used to remove weeds in some cases.
Since all of the cowpea varieties now in use are susceptible to hairy caterpillar, the only control method, at this time, is to spray a contact insecticide on the hairy caterpillar when it attacks cowpea seedlings.
Strong genetic resistance to cowpea aphid is available but, to date, it has only been incorporated into the variety, Melakh. When other varieties are used, it is necessary to relay on natural biological control or if the plants are young or heavily infested to use sprays of insecticides.
Strong genetic resistance to flower thrips is not yet available. The moderate resistance to flower thrips in Melakh is not sufficiently strong to protect against the large populations of this insect pest that are present in wetter parts of Senegal. Where flower thrips are present an insecticide spray can be applied when the plants begin to produce floral buds, and are showing feeding damage on the stipules. A second spray may be applied 7 to 10 days later if there are 9 or more adult thrips per flower. For the major production zone north of Bambey, use of insecticides to control flower thrips often is not necessary but can increase grain yield in some cases.
Most of the landraces have resistance to bacterial blight but are susceptible to cowpea aphid-borne mosaic virus. Use of resistant varieties is the only effective control method against these two diseases. The new varieties Mouride and Melakh are resistant to both bacterial blight and cowpea aphid-borne mosaic virus. The massive introduction of the susceptible variety CB5 has shown the problems that can arise due to susceptibility to bacterial blight in Senegal. These diseases are seed-borne, and fields used to produce seed of the susceptible varieties must not have significant infection with bacterial blight or cowpea aphid-borne mosaic virus. Several other mosaic virus are present in Senegal, which can cause leaf mottling symptoms, including southern bean mosaic, cowpea severe mosaic, and cowpea mottle virus, but these other viruses do not appear to be widely distributed. Until now no symptom of viral diseases has been observed on the variety Bambey 21.
Recent research indicates that a crop of pearl millet can significantly reduce the levels of the sclerotia of Macrophomina phaseolina in the soil that are responsible for the charcoal rot disease. Consequently, annual rotations of pearl millet followed by peanut followed by pearl millet followed by cowpea have the potential to suppress the fungus sufficiently to reduce the extent of the disease on cowpea.
After harvesting which is still done by hand, grains must be protected against bruchid damage. After threshing grain may have to be disinfected. The most practical method for farmers is to use a solar heater. Solar heaters are constructed using a bottom layer of black plastic to absorb solar radiation and a covering of clear plastic to trap heat. Late in the morning of a sunny day, a black plastic sheet is placed on a layer of dry grass, which reduces transfer of heat into the soil. A layer of grains is placed on the black plastic sheet and covered by a transparent plastic sheet, which is held in place with logs or bricks. Within four hours the grain will become hot enough (57 to 70oC) to kill all stages of the cowpea weevil without harming the germination capacity of the seed. The grain should be removed from the solar heater in the late afternoon of the same day.
The cowpea bruchid can be killed by anaerobic conditions and storage in airtight containers is an effective way to eliminate the insect population in stored cowpeas. After disinfestations or even without, grain can be stored in airtight metal drums. The grain should be dried to a moisture content of about 10 % prior to placing them in the drums and the drums should be filled with grain and then placed in the shade. These containers not only prevent re-infestation but they also can kill all stages of the bruchid present on or in the grain if they are kept closed for at least two months. During this period, respiration of the seed and any insects that are present reduces the oxygen concentration and increases the carbon dioxide concentration to levels that kill the weevils but do not harm the germination capacity of the seed.
Flood-water recession system
In the improved flood-water recession system weeding is done just before the field is flooded. Weed destruction is completed by flooding, and the soil surface is then clean when the flood water recedes. The field should be planted as soon as possible because any delay would lead to loss of plant vigor, since the amount of stored soil water diminishes with time. Seed treatment with fungicides can be beneficial and seeds should be sown in rows at 1 x 1 m spacing. A single hand hoeing may be necessary to facilitate plant emergence. With these improvements grain yield can be doubled compared with the average yield of the traditional system.
Cowpea germplasm explorations during the 50’s and 60’s emphasized the main cowpea production areas (regions of Louga, St Louis, Thies and Diourbel). The south-central, eastern and southern zones, which are minor cowpea production areas, were not thoroughly visited. About 60 landraces have been identified as having been cultivated. Today, only five are in significant use as varieties: 58-57, Mame Penda, Mame Fama, Ndout and Baye Ngagne.
Stuart et al. (1990) have identified the following as parts of the cause of the decline in biodiversity. a) Human population pressure accentuated by improvement in health, sanitation and standards of living has resulted in increasing pressure on resources for many development activities. b) Food production methods and practices involving technologies such as slash-and-burn fallow systems that depend on expansion of area under cultivation for increasing agricultural productivity and overgrazing in Savanna areas has resulted in land degradation and desertification. c) Climatic changes, such as in the Sahel where prolonged periods of drought were not matched with appropriate responsive changes in land use or production systems, resulted in environmental degradation. d) Introduction of new varieties that have displaced landraces and/or new production practices that displaced traditional production systems such as intercropping systems.
Human population is increasing in Senegal at the rate of 2.6 % per year. This growth rate is extremely fast and could result in a population doubling time of 27 years. The rural population represented about 53 % of the total in 1999. The consequence is that many of the trees have been removed in the northern zone. Further, fallow lands have virtually disappeared limiting the extent of grazing areas in the main cowpea zone, and leading to permanent conflicts between cultivators and herders. This situation has been traditionally a limiting factor for the extension of late maturing cowpea varieties and of relay intercropping because livestock often grazed on the young cowpea plants.
The droughts occurring in the Sahel since 1968, have considerably reduced the length of the growing season from about 90 to 60 – 75 days. Consequently, late-maturing varieties and the relay intercropping system have frequently failed to produce much grain. Farmers have selected principally the varieties Mame Penda, Mame Fama and 58-57, which mature in 70 to 75 days in sole cropping, to adapt to the climatic change. The relay intercropping with Baye Ngagne and Ndout, which was predominant in the Bambey–Thies area has nearly disappeared. Drought has also negatively impacted the natural vegetation in the northern zones such as the loss of Acacia albida trees that are very beneficial to agriculture.
Introduction and adoption of early varieties, which mature in 60 to 68 days, have contributed to the reduction of the array of cowpea landraces in cultivation. Due to droughts in 1982, 1983 and 1984 and a shortage of peanut and cowpea seed, the 60-day variety CB5 was introduced from California in a drought relief program which lasted until 1987. Two additional early varieties (Mouride and Melakh) were subsequently released in the early 90’s and widely adopted, contributing to the reduced use of landraces.
Cropping systems and technology change have great impacts on the type of varieties used. Peanut has been widely promoted as a cash crop in Senegal since the 20’s. It has been successfully established on large areas of the central and northern regions, which was given the name the “peanut basin”. Subsistence diversification between crops, livestock products, and the collection of wild foods, previously prevailed as a strategy to mitigate risk. Pearl millet and sorghum had been the dominant crops in the system. Peanut acreage rapidly spread to occupy approximately 50 % of cultivated land in this area by the 50’s. In some cases to enhance product diversification, cowpea seed was mixed at a low proportion with the peanut seeds and hand planted. From the 60’s the mixture was planted with a horse-drawn planter. This approach has the advantage of planting the seed in rows, which facilitates the use of horse-drawn cultivators to control weeds. More erect types of peanut were introduced and mechanical weeding made it ineffective to mix spreading cowpea landraces with these new peanut varieties.
Others threats to cowpea genetic resources have come from insect pests. Massive attacks of hairy caterpillar and grasshoppers have caused complete crop loss over vast areas of the main cowpea zone on several occasions. Flower thrips have caused major losses to cowpea production in the center-south, eastern and southern regions discouraging farmers from growing cowpeas. These areas have only been partially visited in previous collection expeditions.
Adequate ex situ conservation of the cowpea collection already acquired has become a high priority. Current facilities for cowpea germplasm conservation at the national agriculture research center at Bambey are not adequate. Recently several needed accessions were lost due to break down of the air conditioner in the storage facility and replacements had to be obtained from duplicate samples held at the University of California, Riverside. Unfortunately, duplicate samples are not available in foreign institutions for all of the Senegal cowpea collection.
4- Venues for Improving Traditional Systems
Substantial collection of cowpea germplasm has been done in the northern zone of Senegal. More cowpea germplasm collection is needed in the center-south, eastern and southern regions. Adequate ex situ conservation facilities for cowpea germplasm should be developed in Senegal. The collected materials should be evaluated for resistance to important insect pests and diseases. The southern and eastern zones have high rainfall and large populations of flower thrips and other pests and diseases that limit the cultivation of cowpea. Only about 6 % of cowpea area and production occur in these zones. Landraces cultivated in these areas have long cycles and partially escape pod rot diseases and the period when flower thrip populations are highest. These landraces have been used in intercropping with cereals. Today this system has almost disappeared due to changes in equipment for cultivation and also to the probable effects of late appearing pod-sucking bugs, such as Mylabris spp., and Anocplocnemis curvipes. New varieties with stronger resistance to flower thrips and pod-sucking bugs might permit greater cultivation of cowpea in these zones. Cowpea production with such varieties in these wetter environments would provide some security for years like 2002 when crop failure occurred in the north due to severe drought.
The reduction of the number of landraces cultivated in the main cowpea zone, from about 60 to 5 is a universal process. Swanson et al. (1994) reported that the number of rice varieties cultivated in Sri Lanka and India has gone from 2,000 and 30,000 to 5 and less than 10 respectively. In the USA, 50% of the wheat crop are in 9 varieties and 75% of potato are in 4 varieties.
Landraces, Ndout and Baye Ngagne are now frequently at risk of crop failure, with the short growing seasons experienced since 1968, because of their photoperiod-sensitivity. Mougne was bred to obtain a 75-day variety with the grain type of Ndout and Baye Ngagne. However, the seed size of Mougne is significantly smaller with a 100-seed weight of approximately 14g, compared with about 22g for the landraces. Consequently, a medium-maturing Mougne-type variety with large grain size and resistance to bacterial blight, cowpea aphid-borne mosaic virus, cowpea aphid and flower thrips should be bred.
Mame Penda is under risk of low yield because the northern part of the cowpea zone where it is grown is dry with a short rainy period. The development of 60-day varieties with appropriate grain types and resistance to prevailing biotic constraints would enhance cowpea production. For this objective, the new line ‘ISRA-819’ has been developed. ‘ISRA-819' was derived from a cross between ‘Melakh’ and the landrace ‘Mame Penda’. Selections were made to obtain an erect plant with the same earliness and resistance to cowpea aphid, bacterial blight and cowpea aphid-borne mosaic virus as ‘Melakh’ and large brown grain. The line ‘ISRA-819' has similar erect morphology and early flowering as ‘Melakh’ but the grain type of Mame Penda. ‘ISRA-819' has seed that are brown and large (100-seed weight of 23g), whereas ‘Melakh’ has seed that are white with a brown eye and of moderate size (100-seed weight of 19g). Unfortunately, ‘ISRA-819' is more sensitive to flower thrips than is ‘Melakh’. Consideration is being given to recommending release of ‘ISRA-819' as a cultivar in northern Senegal where flower thrips are not a major pest problem.
The high rate of population growth in Senegal coupled with rapid urbanization (in 1999 47 % of the population was urban) and deteriorating environmental conditions necessitated larger outputs from agriculture. Cropping systems and technology changes that have taken place in the ‘peanut basin’ have substituted subsistence diversification between crops and livestock products with sole-crop production systems. This process has led to reductions in the number of landraces cultivated by capitalizing on the benefits resulting from the uniformity of the variety itself. This uniformity renders the variety combinable with other factors of production in modern agriculture such as mechanized sowing and weeding, optimum use of fertilizers, manure and pesticides, and effective use of rotations that can bring multiple benefits. The substitution of subsistence diversification has generated a net loss in diversity. The maintenance of some diversity in agriculture can protect plant genetic resources and enhance the stability of the agricultural system. Cowpea diversity can be enhanced by approaches, such as the use of cultivar blends, multiline cultivars, and varietal intercropping. In the context of the cowpea production areas of northern Senegal, the major objective should be to enhance resistance to drought. Medium-cycle spreading and early erect varieties could be grown together in alternating rows as varietal intercrops to provide some resistance to both mid-season and terminal droughts. These varieties also should have resistances to many biotic constraints. The blending or intercropping of the medium-cycle spreading landrace Mame Penda and the early erect line ‘ISRA-819’ might result in greater and more stable yields. Likewise white-seeded spreading varieties, which mature in 75 days after planting, should be developed to complement Melakh in varietal intercrop systems of cultivation.
With the rapid urbanization, more widespread consumption in cities of convenience foods containing significant amounts of cowpea would substantially increase the demand and value of cowpea grain. New constraints define food preferences and needs of the urban population. With a high percentage of urban women entering the work force to increase family income, time for cooking becomes an increasingly important factor in the selection of foods. Child nutrition among the urban poor is also becoming a major concern. The demand for cowpea grain and processed products is dictated by consumer and industry preferences and needs as a result of these urban realities. The food technology institute in Senegal (ITA) has developed and tested four products namely: precooked grain, toasted grits and flour, and dry flour in restaurants and households (Hamdy, 1989). All products were highly acceptable to consumers. Dry flour was exclusively prepared into ‘Akara’, a fried ball of whipped cowpea paste that is usually seasoned with chopped fresh peppers (hot or mild) and other spices or seasonings. Traditionally akara paste is prepared by first soaking cowpeas followed by manual removal of seed coats and then milling of the wet grain. The time necessary from soaking through frying can be as much as 24 hours. With dry flour only about 30 minutes would be required to prepare the batter and fry the akara. This process would be much more convenient for the cook and provide more consistent quality to the consumer than the traditional process. Dry milling of whole grains would be much more efficient than the traditional labor-intensive process and dry flour could be stored longer than wet paste. The use of cowpea flour milled from all-white grain may be more desirable than flour from pigmented grain. Grain of ‘Bambey 21' is different from most other cowpea grain in that it lacks any type of pigment. Other cowpeas that have white seed coats also have a pigmented ring around the hilum that results in the presence of undesirable specks in the flour of milled whole grains. Precooked grains have been used in salad or ragout preparations with sauce recipes. The concept of marketing precooked, dry cowpeas is based on two major advantages to consumers: convenience in preparation, and quality at a reasonable price. Precooked, dry Bambey 21 grain will cook in 15 minutes, and has a quality equal to cooked white beans. Toasted grits could be used in a well-known recipe called ‘Neleng’ that resembles pearl millet couscous, and usually is served with tomato and peanut butter sauce. Toasted flour could be served in the form of agglomerated granules called ‘thiakry’ with sweetened butter- milk, or as couscous, or as a thickener in sauces.
These cowpea products were analyzed for chemical, functional, and nutritional characteristics. Precooked, dry Bambey 21 grain had good overall quality and from a nutritional aspect was similar to the landrace 58-57 and the introduced variety CB5. Cooking the grain improved protein digestibility, and practically eliminated inherent anti-metabolites such as phytic acid and trypsin inhibitors. Cooking also reduced the level of oligosaccharides, particularly stachyose, responsible for flatulence. Toasted products and dry flour were not significantly changed in their contents of the latter elements, however when cooked their nutritional quality was significantly improved. In 2003, micro-enterprises such as ‘La vivriere’, ‘Conserverie du Senegal’, and ‘Les grands moulins du Cayor’ were marketing cowpea-based products, such as weaning food, flour and canned ‘Ndambe’. However, the capacity of these enterprises was small relative to the need. Technological support for micro- and intermediate-scale entrepreneurs involved in adding value to commodities is extremely limited. The agribusiness sector has yet to receive the attention and financial support that the supply side of agriculture has received.
Bambey 21 has proven to have good qualities for producing flour but is poorly adapted to the drought-prone area of cowpea production, and is susceptible to bacterial blight and insect pests such as cowpea aphid and flower thips. There is then the need to develop cowpea varieties with desired quality traits for home consumption and processing that have good adaptation. These cultivars should be adapted to drought and specific agro-ecological conditions, and resistant to economically important pathogens and insect pests. Little is known about the grain quality of the preferred landraces Mame Penda, Ndout, and Baye Ngagne. There is a need to investigate the processing and packaging attributes of these varieties.
Different cowpea varieties can have different taste. Taste panel tests conducted at Purdue University showed that US tasters, who were generally unfamiliar with cowpeas, chose a “sweet” Cameroonian Line ‘C93W-24-125B’ more than 80% of the time over conventional varieties. Line ‘C93W-24-125B’ has been shown to have a sucrose content of about 6% (w/w) compared to about 2% (w/w) for typical cowpea varieties. Informal taste tests conducted at UCR indicated that the “Hopping John” dish made using ‘C93W-24-125B’ had a more pleasant “nutty” taste and firmer texture than the same dish made with California blackeye-type cultivars but that ‘C93W-24-125B’ did not have a distinct sweet flavor like a fresh garden pea (Pisum sativum L.). A 1990 report by ITA in Dakar, Senegal noted that a sensory panel preferred the taste of ISRA breeding line, ‘283 N’, over three cultivars, ‘CB5', ‘Bambey 21' and ‘Mouride’ because of the “sweet” taste of ‘283 N’. Apparently, the “sweet” trait could be a valuable flavor trait that breeders could use to enhance the desirability of cowpea cultivars for both traditional cowpea consumers and consumers to whom cowpea is less familiar.
In African countries, the need for locally produced, high quality, nutritious, and safe processed foods is critical as urban spending power and the opportunity cost of women’s time increase. Since the food processing industry in many African countries is still in its infancy, opportunities also exist, at least in the near future, to supply other African markets with value-added food products. However, such products must incorporate indigenous commodities of the region, be developed to conform to regional tastes and dietary habits, and be affordable to wide portions of the population. Since cowpea is such an important staple throughout most of West Africa, cowpea-based food products are considered to have high market potential within the region. The need for the emergence of a strong local processing industry is especially acute in Africa because of declining commodity prices. Off-farm processing would add value to cowpea grain, and provide new marketing opportunities for small-scale farmers. Cowpea grain trade among countries within Africa is an excellent means to expand markets as well as incomes for small-scale farmers. If producers and traders had greater inter-country market information relative to commodity availability, quality and prices, transaction costs could be reduced and more informed decisions could be made relative to grain storage and marketing strategies. Cowpea varieties need to be developed for use by farmers in Senegal that have grain types favored by the export markets to neighboring countries. Markets are present for cowpea grain that is large and white and has a rough textured seed coat.
Success of food enterprises is largely contingent upon the ability of the production sector to provide cowpea grain with the desired quality attributes, in sufficient quantities consistently over time, and at competitive prices to satisfy target markets. To achieve these ends, new technologies are needed for small-scale farmers to increase crop yields, achieve greater efficiencies, and thus economies, within the farming system. At the same time, agronomic research to increase crop productivity must emphasize conservation and effective management of the natural resource base. Natural resource conservation must be reflected in the selection of resistance and efficiency traits to be bred into new cowpea varieties, in the approaches used for meeting crop mineral nutrient requirements and managing the soil, and in the formulation of integrated pest management strategies for cowpeas. More sustainable approaches are needed, in particular, to meet requirements for P, one of the most yield limiting factors in Senegal. Genetic approaches to improve P uptake efficiency and utilization in low P soils by cowpea has the potential to enhance the sustainability of the whole cropping system. There is a strong likelihood that nematode pests contribute to the inadequate uptake of minerals by cowpea and other crops. Nematode infection reduces the functioning of root systems in uptake of water, nutrients and minerals. Recent surveys have shown that five different genera of nematode pests are present in cowpea fields throughout the center-north and north of Senegal. The specific types of nematodes and the extent to which they damage cowpea and other crops must be determined in order to target genetic improvement in cowpea to incorporating resistance to the most damaging nematode pests. The extent to which nematode-resistant cowpea varieties also benefit other crops grown in rotation also should be determined as part of management systems designed to make the whole cropping system more sustainable. Strong resistance to nematode pests has been discovered in cowpea especially by research at the University of California, Riverside. Control of the parasitic weed Striga gesnerioides also would enhance the mineral nutrition of cowpea. Development of resistant cowpea varieties is the most efficient method for controlling this pest. Crop rotations that include non-susceptible crops and those that cause suicidal germination of Striga seed can help in reducing the numbers of the seed in the soil of the Striga species that can damage cowpea, pearl millet and sorghum. Rotations could be very effective if the varieties and crops that are used, cause germination of the parasitic weed but do not allow it to grow and produce seed. Some varieties of cowpea have been shown to cause suicidal germination of the seed of the Striga species that damages pearl millet and sorghum.
Concurrent investment in extension efforts to disseminate and demonstrate these technology packages should be undertaken so that farmers have ready access to seed of improved cowpea varieties and knowledge of the advantages conferred by these varieties and of their unique cultural requirements.
Poor nutrition has been clearly identified as contributing to many forms of human diseases. Increasingly, impoverished people who live in cities have the most nutritionally poor diets because of high consumption of fatty and sugary convenience foods and the lack of a diverse diet containing nutrient-rich foods such as cowpea and vegetables. Cowpeas are among the most healthful and nutritious plant foods. In addition to their high protein, vitamin B and mineral nutrient compositions, cowpea seed coats contain flavonoids, the same anti-oxidants found in fruits and vegetables, which protect human cells from damage caused by free radicals. Traditional foods that include nutrient-rich cowpeas can be healthy and need to be promoted, especially as urban populations grow.
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