Prota 14: Vegetable oils/Oléagineux
Interpr. Herb. amboin. 274 (1917).
Papilionaceae (Leguminosae - Papilionoideae, Fabaceae)
2n = 40
Glycine hispida (Moench) Maxim. (1873).
Soya bean, soybean (En). Soja, soya (Fr). Soja (Po). Soya (Sw).
Origin and geographic distribution
Soya bean was domesticated in the north-east of China around the 11th century BC. From there, it spread to Manchuria, Korea, Japan and other parts of Asia. Soya bean was introduced into Korea between 30 BC and 70 AD, and it was mentioned in Japanese literature around 712 AD. It reached Europe before 1737. Soya bean was introduced into the United States in 1765 and into Brazil in 1882. It is unclear when soya bean first reached tropical Africa. There are reports of its cultivation in Tanzania in 1907 and Malawi in 1909, but it is likely that soya bean was introduced during the 19th century by Chinese traders who were active along the east coast of Africa. Nowadays, soya bean is widely cultivated in tropical, subtropical and temperate regions throughout the world. The slow distribution outside Asia is explained by the absence of soya bean specific rhizobia in the soils of other regions; the crop only developed in the United States at the beginning of the 20th century, following the discovery of the nodulation process by scientists.
In tropical Africa dry soya bean seeds are boiled for use in relishes, or used in the preparation of milk substitutes and flour. A popular use of soya bean milk in Nigeria is to make a tofu-like product that is deep fried and sold as a snack or breakfast food. The flour is used as a component of bread or mixed with maize flour to make a fortified porridge (‘ugali’, ‘sadza’). In West Africa soya bean flour is used to thicken soup and to replace a traditional flour that is made from the seed of egusi melon (Citrullus lanatus (Thunb.) Matsum. & Nakai). ‘Okara’ is the pulp and bran left over from making soya milk; this cake is used in almost all the same ways as soya bean flour. Soya bean seeds are dry roasted and used directly as a snack or as a coffee substitute. The seed is also milled into flour and mixed with maize meal to serve as a relief food during famine. In Asia soya bean is used in the preparation of a variety of fresh, fermented and dried food products like milk, tofu, tempeh, miso, yuba, soya sauce and bean sprouts (soya bean sprouts are meant here, and not mung bean sprouts, which are more common in Western countries, and which are often called ‘germes de soja’ in French). Immature soya bean seeds are eaten as a vegetable.
Soya bean seed is processed to extract oil for food and for numerous industrial purposes; the crop is currently the world’s most important source of vegetable oil. The edible oil enters the market as cooking oil, salad oil, margarine and shortening. Soya bean lecithins are used as emulsifier in the food industry, in pharmacy, and in the industrial production of decorating materials, printing inks and pesticides. Soya bean oil is the main commercial source of α-tocopherol (natural vitamin E) and contains stigmasterol, which is used for the commercial synthesis of steroid hormones and other pharmaceutical products. The cake remaining after oil extraction is rich in protein and is an important animal feed. Uses of soya bean proteins in food include defatted flours and grits, concentrates, isolates, textured flours and textured concentrates (commonly used as meat extender). The protein is also used in the production of synthetic fibres, glues and foams.
Soya bean is also grown as fodder and as green manure; it is suitable for haymaking and silaging. The leafy stems remaining after pod removal can also be used as fodder.
Production and international trade
According to FAO estimates, the average world production of soya bean seeds is 173 million t/year from 77 million ha (mean of 1999–2003). The main producing countries are the United States (73.5 million t/year in 1999–2003, from 29.4 million ha), Brazil (39.0 million t/year from 15.1 million ha), Argentina (26.4 million t/year from 10.2 million ha), China (15.4 million t/year from 9.0 million ha), India (5.9 million t/year from 6.3 million ha), Paraguay (3.4 million t/year from 1.3 million ha) and Canada (2.3 million t/year from 1.0 million ha). South Africa produced 188,000 t/year from 121,000 ha. The soya bean production in tropical Africa in 1999–2003 was 790,000 t/year from 895,000 ha, the main producers being Nigeria (439,000 t/year from 601,000 ha), Uganda (139,000 t/year from 124,000 ha) and Zimbabwe (119,000 t/year from 62,000 ha).
Average world export of soya bean seeds amounted to 47.4 million t/year in 1998–2002, the main exporters being the United States (25.4 million t/year), Brazil (12.3 million t/year) and Argentina (4.7 million t/year). Export of soya beans from tropical Africa was only 27,000 t/year, with Zimbabwe as main exporter (11,000 t/year). The main importer was China (11.0 million t/year). Soya bean import in tropical Africa was 37,000 t/year. Average world export of soya bean oil in 1998–2002 was 8.2 million t/year, with as main exporters Argentina (3.0 million t/year), Brazil (1.5 million t/year) and the United States (0.9 million t/year). The export of soya bean oil from tropical Africa was negligible. The main importers in 1998–2002 were China (975,000 t/year), India (837,000 t/year), Iran (701,000 t/year) and Bangladesh (522,000 t/year). Soya bean oil import in tropical Africa in 1998–2002 amounted to 338,000 t/year, the main importing countries being Senegal (83,000 t/year), Angola (39,000 t/year), Mauritius (25,000 t/year), Madagascar (22,000 t/year) and Zimbabwe (22,000 t/year). Average soya bean cake export amounted to 40.8 million t/year, with as major exporters Argentina (13.6 million t/year), Brazil (10.8 million t/year) and the United States (6.4 million t/year). Soya bean cake export from tropical Africa was 30,000 t/year, mainly from Zimbabwe (14,000 t year) and Zambia (12,000 t/year). The main importers were countries of the European Union. Tropical Africa imported 72,000 t/year.
Soya bean is grown by smallholders in many countries of West, East and southern Africa, though normally as a minor food crop. Commercial soya bean production on large farms and estates is common in Zambia and Zimbabwe, and also in South Africa.
The composition of mature raw soya bean seeds per 100 g edible portion is: water 8.5 g, energy 1742 kJ (416 kcal), protein 36.5 g, fat 19.9 g, carbohydrate 30.2 g, dietary fibre 9.3 g, Ca 277 mg, Mg 280 mg, P 704 mg, Fe 15.7 mg, Zn 4.9 mg, vitamin A 0 IU, thiamin 0.87 mg, riboflavin 0.87 mg, niacin 1.6 mg, vitamin B6 0.38 mg, folate 375 μg and ascorbic acid 6.0 mg. The essential amino-acid composition per 100 g edible portion is: tryptophan 530 mg, lysine 2429 mg, methionine 492 mg, phenylalanine 1905 mg, threonine 1585 mg, valine 1821 mg, leucine 2972 mg and isoleucine 1770 mg. The principal fatty acids are per 100 g edible portion: linoleic acid 9925 mg, oleic acid 4348 mg, palmitic acid 2116 mg, linolenic acid 1330 mg and stearic acid 712 mg (USDA, 2004). Soya bean seeds have a protein content higher than any other pulse. The seeds have a high lysine content; the limiting amino-acid is methionine. Mature soya bean seeds are not easily digested, contain toxic compounds and have an unpleasant taste. Therefore they must be soaked and cooked for a long time before being edible, or be processed by techniques such as roasting, fermentation or sprouting. Heat-labile antinutritional factors of soya bean are trypsin inhibitors, haemagglutinins, goitrogens, antivitamins and phytates, and heat-stable ones are saponins, oestrogens, flatulence factors and lysinoalanine.
Yield of meal from soya bean seeds is 80% and of oil 18%. The meal contains about 50% protein. The average fatty acid composition of commercial soya bean oil is: linoleic acid 54%, oleic acid 22%, palmitic acid 10%, linolenic acid 10% and stearic acid 4%. Soya bean oil is rich in vitamin E and contains 1.1–3.2% lecithins. Soya bean seeds are always heat-treated before oil extraction, because of the presence of antinutritional compounds. Soya bean oil tends to become rancid when exposed to air or light, due to the instability of the linolenic acid. The protein and oil concentrations of soya bean are negatively correlated, and efforts to raise both simultaneously have been unsuccessful. The oil content tends to increase with increasing temperature during growth, whereas the protein content tends to decrease.
Consumption of soya bean is associated with decreased risk of atherosclerosis and cardiovascular disease, although the exact mechanisms are not clear. There are also indications that soya bean has a positive effect on bone health. The relation between soya bean consumption and reduced risk of cancer is more uncertain.
Usually erect, bushy annual herb up to 2 m tall, sometimes viny; taproot branched, up to 2 m long, lateral roots spreading horizontally to a distance of up to 2.5 m in the upper 20 cm of the soil; stem brownish or greyish pubescent. Leaves alternate, 3(–7)-foliolate; stipules broadly ovate, 3–7 mm long; petiole 2–20 cm long, especially in lower leaves; leaflets ovate to lanceolate, 3–15 cm × 2–6(–10) cm, base cuneate or rounded, apex acute to obtuse, entire, glabrous to pubescent. Inflorescence an axillary false raceme up to 3.5 cm long, often compact, densely hairy, (2–)5–8(–35)-flowered. Flowers bisexual, papilionaceous; pedicel up to 3 mm long; calyx tubular, with 2 upper and 3 lower lobes, hairy; corolla 5–7 mm long, white, pink, purple or bluish, standard obovate to rounded, c. 5 mm long, glabrous, wings obovate, keel shorter than the wings; stamens 10, 9 fused and 1 free; ovary superior, style curved with head-shaped stigma. Fruit a slightly curved and usually compressed pod 2.5–8(–15) cm × 1–1.5 cm, hairy, dehiscent, (1–)2–3(–5)-seeded. Seeds globose to ovoid or rhomboid, 6–11 mm × 5–8 mm, yellow, green, brown or black, or blotched and mottled in combinations of those colours; hilum small, black, brown or yellow. Seedling with epigeal germination; cotyledons thick and fleshy, yellow or green; first leaves simple and opposite.
Other botanical information
Glycine comprises about 20 species distributed in the tropics and subtropics of Asia and Australia. It is divided into 2 subgenera: Glycine (perennials) and Soja (annuals), with the latter including 2 species: Glycine soja Sieb. & Zucc. (wild types, occurring in eastern Asia) and Glycine max (cultivated types). Glycine soja is considered the wild ancestor of Glycine max. The 2 taxa hybridize easily and may also be considered a single species with 2 subspecies, Glycine max (L.) Merr. subsp. max and subsp. soja (Sieb. & Zucc.) Ohashi.
Numerous cultivars are recognized in tropical Asia that vary in time to maturity, size, plant habit, colour, content of oil and protein in the seed, and uses to which they are put. For oil production, yellow seeds are preferred. For immature seeds to be used as a vegetable, types with large yellow or green seeds are preferred. Hay and fodder cultivars usually have brown or black seeds and the plants often twine. In tropical Africa the older cultivars that originated from Asia tend to be tall and indeterminate in growth habit, take comparatively long to mature (about 120 days) and are ‘promiscuous’ in their ability to nodulate with rhizobia indigenous to African soils. These cultivars can be contrasted with soya bean cultivars that have emerged from breeding programmes and tend to be short-statured, determinate, and relatively fast-maturing (70–90 days).
Growth and development
Soya bean seedlings emerge within 5–15 days after sowing; a seedbed temperature of 25–33°C is optimal. Flowering starts from 25 days to more than 150 days after sowing, depending on daylength, temperature and cultivar. Flowering can take 1–15 days. Soya bean is normally self-pollinated and completely self-fertile with less than 1% cross-pollination. Pollen is normally shed in the morning, before the flowers have completely expanded. At higher altitudes with lower temperatures, flowers are usually cleistogamous. The time from flowering to pod maturity is 30–50 days. The total crop cycle from sowing to maturity is 65–200 days. Development to maturity is usually shorter with short days than with long days. The number of pods per plant varies from a few to more than 1000.
Although older literature indicates that soya bean is nodulated exclusively by slow-growing rhizobia (Bradyrhizobium spp.; initially called ‘cowpea-type rhizobia’) it is now well established that the fast-growing Sinorhizobium fredii can also form effective nodules with the crop. Soya bean genotypes differ enormously in their ability to nodulate with indigenous rhizobia in soils. The ability to nodulate spontaneously and prolifically with indigenous rhizobia is known as the ‘promiscuous’ character, compared with the ‘specific’ character of soya bean types that normally require inoculation with a specific type or with a few specific types of rhizobia in order to grow well. However, it has now been established that all soya bean genotypes nodulate to some extent with indigenous rhizobia, but the diversity of strains with which they can nodulate determines the extent of their promiscuity. Rates of N2-fixation in soya bean are greatest in the more luxuriant and late maturing genotypes. Studies conducted in Nigeria have measured a N2-fixation rate of 126 kg of N per ha for an uninoculated late-maturing soya bean line.
Soya bean is grown from the equator to latitudes 55°N or 55°S, at altitudes from close to sea level up to 2000 m. Although the crop grows well under a wide range of temperatures, the optimum temperature for growth and development is in general around 30°C. Both excessively 32°C) and low (<20°C) temperatures can reduce floral initiation and pod set. Soya bean requires at least 500 mm water during the growing season for a good crop; water consumption under optimal conditions is 850 mm. Drought stress during flowering reduces pod-set but drought during pod-filling reduces yield even more. Soya bean can tolerate brief waterlogging but weathering of seed is a serious problem under humid conditions. Soya bean is considered a quantitative short-day plant, but some cultivars are insensitive to photoperiod. The response to photoperiod interacts strongly with temperature, and given the relatively small variation in daylength in the tropics, temperature is the major factor influencing the rate of phenological development. The photoperiod sensitivity means that types brought directly into tropical Africa from North America will often flower and set seed before they have fully developed, restricting their yields.
Soya bean grows well on most soils, except very coarse sands. The optimum pH is 5.5–7.5, and soya bean is sensitive to soil acidity, in particular to aluminium toxicity. Where soya bean has not grown previously, or where P is limiting, symbiotic N2-fixation may be inadequate to meet the N requirement of the plants.
Propagation and planting
Soya bean is propagated by seed. The 1000-seed weight is 100–250 g. The seed can be sown before the start of the rainy season, or when the soil is moist. Seed rates are 40–120 kg/ha. Soya bean is sown in rows (20–)40(–75) cm apart. Within the rows, 2–3 seeds are sown in hills spaced at 7.5–10 cm intervals, at a depth of 2–5 cm. With intercropping, sowing rates are less than for sole cropping. In traditional agriculture the land is prepared by hand or animal traction before sowing. Soya bean is grown mainly on the flat, but sowing on hills or ridges may be practised where the soil is heavy, the water table high, or rainfall heavy. Small-scale farmers in tropical Africa grow soya bean as a sole crop or in mixed cropping with maize, sorghum or cassava.
Soya bean is usually weeded 1–3 times during the first 6–8 weeks after planting, after which its canopy should be sufficiently developed to suppress weeds. Irrigation is uncommon except for dry season production. Basal fertilization with 20–25 kg P per ha is often required for adequate symbiotic N2-fixation and general growth. Soya bean is commonly grown in rotation with cereals, such as maize, rice, sorghum, wheat and finger millet, whereby all fertilizer may be applied to the cereal.
Diseases and pests
Various fungal diseases affect soya bean. Soya bean rust (Phakopsora pachyrhizi and Phakopsora meibomiae) is a devastating disease that can reduce yields by as much as 90%. It is widespread; in tropical Africa it is recorded from Sierra Leone, Ghana, Nigeria, DR Congo, Uganda, Tanzania and Zambia. Partial resistance has been found in various cultivars; fungicides may reduce damage. Red leaf blotch (Dactuliochaeta glycines, synonym: Pyrenochaeta glycines) is confined to Africa; it is economically important in Zambia and Zimbabwe, where yield losses of up to 50% have been recorded. Seeds are not infected, but the fungus can survive in the soil for many years. Tolerant cultivars have been developed in Zimbabwe. Frogeye leaf spot (Cercospora sojina, synonym: Passalora sojina) occurs worldwide. It is primarily a leaf disease, but it may also affect stems, pods and seeds. It survives on stored seeds and crop residues and is spread by wind. Control measures include seed treatment (e.g. with thiram), deep-ploughing of crop residues, crop rotation and application of fungicides. Resistant cultivars are available. Purple seed stain and leaf blight are caused by Cercospora kikuchii, also occurring worldwide. Recommended control measures are crop rotation, the use of clean seed, ploughing back of crop residues, spraying with fungicides and the use of tolerant cultivars. Among the bacterial diseases of soya bean, bacterial blight (Pseudomonas syringae pv. glycinea, synonym: Pseudomonas savastanoi pv. glycinea) is common wherever soya bean is grown. Control practices of this foliar disease include the use of resistant cultivars, the use of clean seed, crop rotation and burying of crop residues. Bacterial pustule (Xanthomonas campestris pv. glycines, synonym: Xanthomonas axonopodis pv. glycines) is also widespread. It is seed-transmitted and survives on crop debris. Control measures are similar to those of bacterial blight. Virus diseases of soya bean include soya bean mosaic virus (SMV), cowpea mild mottle virus (CPMMV) and bean yellow mosaic virus (BYMV), but these are of little importance in tropical Africa.
Soya bean cyst nematode (Heterodera glycines) and root-knot nematodes (Meloidogyne spp.) can cause severe damage, especially on sandy soils. Therefore, soya bean should not be grown continuously or in rotation with other susceptible crops, such as tobacco. Soya bean cultivars resistant to nematodes are available.
The most widespread and probably most serious pest of soya bean in tropical Africa is the southern green stink bug or soya bean green stink bug (Nezara viridula), of which the nymphs and adults feed on soya been seeds. Control is by using insecticides. The most important leaf-eating pest is probably the soya bean looper (Xanthodes graellsii). Bean flies (mainly Melanagromyza sojae and Ophiomyia centrosematis) can cause complete yield loss. Soya bean seedlings are occasionally damaged by cutworms (Agrotis spp.). No major storage pests are recorded from Africa, except rodents.
Mature seeds of early-maturing soya bean cultivars can be harvested 65 days after planting; late maturing cultivars may need more than 150 days. In tropical Africa the plants are generally allowed to dry in the field and the whole plants (above ground) are collected by hand when most leaves have turned yellow and fallen, and when the pods have turned brown. The moisture content of the seeds at harvesting should be 14–15%. Pods of older cultivars have a tendency to shatter in the field when drying and plants need to be harvested on time to prevent major loss of yield. Combine-harvesting is used on large farms and estates. Soya bean seed for vegetable use is harvested when the pods are still green but the seeds fill the pod.
Average world soya bean yields are 2.25 t/ha; those in the United States 2.5 t/ha. Under smallholder farming conditions in tropical Africa yields are often as low as 0.5 t/ha due to a combination of poor soil conditions and poor management. However, yields of more than 2 t/ha have been recorded on smallholder farms in Zimbabwe and Nigeria, particularly when farmers are growing soya bean as a cash crop to sell in urban food markets or for processing for oil and feed. The average yield of commercial, large-scale farmers hovers around 2 t/ha. Under optimal growing conditions yields of more than 4.5 t/ha have been recorded in Zimbabwe. In Nigeria and most of West Africa the yield potential of soya bean is about 3 t/ha.
Handling after harvest
The whole plants are dried in the sun. They are then threshed by beating with sticks. The seeds are winnowed, cleaned and prepared for store or market. For on-farm storage a seed moisture content of 10–12% must be maintained. Deterioration of seed in storage is a major problem in the humid tropics and is attributable to poor storage conditions and pests. In the savanna region of West Africa producers have developed appropriate seed handling methods that ensure good seed germination when they save their own seeds.
The largest germplasm collections of soya bean are held in China (Institute of Crop Germplasm Resources (CAAS), Beijing, 23,600 accessions; Nanjing Agricultural University, Nanjing, 13,000 accessions), the United States (USDA-ARS Soybean Germplasm Collection, Urbana, Illinois, 18,400 accessions) and Taiwan (Asian Vegetable Research and Development Centre (AVRDC), Shanhua, 12,500 accessions). In tropical Africa substantial germplasm collections are held in Zimbabwe (Crop Breeding Institute, Harare, 2250 accessions), Nigeria (International Institute of Tropical Agriculture (IITA), Ibadan, 1800 accessions), Rwanda (Institut des Sciences Agronomiques du Rwanda (ISAR), Butare, 550 accessions) and Kenya (National Genebank of Kenya, Crop Plant Genetic Resources Centre, KARI, Kikuyu, 130 accessions).
Genebank accessions have been successfully used for the improvement of resistance to diseases and pests, plant morphology and seed composition. The genetic variation of soya bean cultivars is rather narrow. For instance, about 80% of the genepool of the soya bean cultivars grown in the United States can be traced to only 7–10 introductions from the same geographical area. It is therefore considered necessary to broaden the genetic base of cultivated soya bean by using wild relatives.
Breeding work on soya bean in tropical Africa aims at the development of improved cultivars with high and stable seed yield, resistance to major diseases and pests, tolerance to aluminium toxicity, resistance to lodging and pod shattering, promiscuous nodulation, improved seed longevity and acceptable seed colour, oil and protein content. A breeding programme at IITA has focused since the early 1980s on combining the yield potential of cultivars bred in North America with the ‘promiscuous’ or ‘naturally-nodulating’ ability of landraces from Asia to form nodules and fix nitrogen without inoculation in African soils. This breeding programme has produced a series of excellent multi-purpose cultivars that combine a leafy growth habit with appropriate seed type and high yield potential. These cultivars are liked by smallholder farmers because they provide biomass for forage or to improve soil fertility in addition to having high seed yields. They are being actively promoted in many countries in East and West Africa at present. In southern Africa similar benefits of a largely unimproved cultivar, ‘Magoye’, were recognized. ‘Magoye’ is a leafy, indeterminate cultivar, relatively resistant to stresses and mid-season drought, that grows better on poor soils than some of the improved cultivars, nodulating well with indigenous rhizobia. Despite its smaller, yellow seed, and susceptibility to some diseases such as bacterial pustule, this makes it an attractive cultivar for use by smallholder farmers in southern Africa.
Research at IITA has identified soya bean breeding lines that favour the germination of Striga hermonthica (Delile) Benth., a parasitic weed that infects maize, sorghum and pearl millet, and one of the major constraints to production of these crops in Africa. The probable cause of this effect of soya bean is the presence of root exudates. The inclusion of these soya bean cultivars in crop rotations stimulates Striga germination and reduces infestation levels in following sorghum, maize or pearl millet crops as a result of the decline of Striga seed numbers in the soil. After germination the Striga plants are unable to infest the soya bean crop, and die without producing seed. A 3-year trial conducted in Benin showed that 2 seasons of soya bean followed by maize reduced Striga hermonthica emergence by about 80–90% and increased maize yield from 1.5 t/ha to 3 t/ha. Similar results have been obtained in farmers’ fields in Nigeria. As soya bean becomes more popular in areas where maize, sorghum and pearl millet are grown, the amount of damage caused by Striga hermonthica should become significantly less.
A number of private seed companies are involved in breeding soya bean in southern Africa, with particular emphasis on cultivars suitable for mechanized production. The companies are targeting a number of traits including high seed yield, resistance to lodging, resistance to pod shattering, rapid stem dehydration, seed quality and resistance to diseases (particularly red leaf blotch and frogeye leaf spot). New cultivars are ‘Solitaire’, ‘Soma’, ‘Soprano’ and ‘Viking’, all of which have some resistance to frogeye leaf spot. These cultivars are all specific in their nodulation ability and require inoculation with the appropriate rhizobia. Inoculants for soya bean are produced, sold and used on a large scale in both Zimbabwe and South Africa.
Soya bean is a leading crop in the field of genetic transformation. In 2001 the world area under transgenic herbicide-tolerant soya bean was estimated at 33 million ha; it was grown in the United States, Argentina, Canada, Mexico, Uruguay, Romania and South Africa. Genetic linkage maps have been constructed for soya bean on the basis of various markers (RFLP, SSR, RAPD, AFLP), and several moderate- to high-density genetic maps are now available. In-vitro regeneration of soya bean is possible through organogenesis and somatic embryogenesis.
Soya bean is a relatively new crop in tropical Africa. It has long been thought that soya bean was not a suitable food crop for the region, because of the long cooking time needed and the unacceptable taste. However, the importance of the crop in tropical Africa has grown rapidly during the past decades. Especially Nigeria witnessed a rapid expansion in soya bean production in the smallholder farming sector in the savanna zone during the 1990s. The driving force for this expansion was the use of soya bean in the preparation of many traditional foods and the introduction of soya tofu which rapidly became one of the most popular snacks in markets in the region and is widely used by the food processing industry. In some areas, the low world prices may depress opportunities for local producers to respond to increased local demand for soya bean. Soya bean can play an increasingly important role in diversifying cereal-based farming systems in tropical Africa. Apart from being a source of residual nitrogen for subsequent cereal crops in crop rotations, the new multi-purpose cultivars bred by IITA provide the additional benefit that they help to reduce Striga hermonthica damage on maize, sorghum and millet, thus representing a major opportunity to provide sustainable crop rotations for smallholder farmers. It is therefore very likely that soya bean production will expand in many tropical African countries in the future.
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Sources of illustration
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Correct citation of this article:
Giller, K.E. & Dashiell, K.E., 2007. Glycine max (L.) Merr. In: van der Vossen, H.A.M. & Mkamilo, G.S. (Editors). PROTA 14: Vegetable oils/Oléagineux. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, flowering branch; 2, fruiting branch; 3, seeds.
drying harvested plants
soya bean products: bean curd, tempeh, oil, butter, dry seeds