Bean Production

Credits: Biovision-Infonet

1. GEOGRAPHICAL DISTRIBUTION IN AFRICA

2. GENERAL INFORMATION AND AGRONOMIC ASPECTS

Many names are used for Phaseolus vulgaris. These include bush beans, common beans, dry beans, dwarf beans, field beans, French beans, garden beans, green beans, haricot beans, kidney beans, pole beans, snap beans or string beans. 

However, presently, two distinct bean types are recognised in the region: French beans (green beans) and common beans (dry beans). French beans are the immature green pods of P. vulgaris and are primarily grown for export market to European Union and elite local urban markets. Common beans are the second most important staple food to maize for the local people. 

Beans were introduced to Africa from Latin America several centuries ago. To date beans are a vital staple in Africa, providing the main source of protein. Common beans are mainly grown by women for subsistence and for the local market. French beans (green/snap beans) are grown as a cash crop by large scale and smallholder farmers. They are a major export vegetable commodity in Eastern Africa. The main producing countries in the region are Kenya, Tanzania, Uganda, and more recently Rwanda. In Kenya, most of the crop is grown by smallholders and virtually all is exported to Europe. Estimates indicate that up to 50,000 smallholder families are involved in French bean production in Kenya. 

The growth habit of common beans varies from determinate dwarf or bush types to indeterminate climbing or pole cultivars. Bush beans are the most predominant types grown in Africa. However, improved climbing beans introduced to Rwanda in the 80’s have since spread to other countries in the region. They are particularly grown in areas with limited land and high human population.

Climatic conditions, soil and water management 

Common beans grow within a range of temperatures of 17.5-27degC. Above 30degC flower buds are likely to fall and seeds are rarely formed at temperatures over 35degC. They are sensitive to night frost. Common beans are usually grown at altitudes between 600 – 1950 m in many tropical areas.

 A moderate well-distributed rainfall is required (300-400 mm per crop cycle) but dry weather during harvest is essential. Drought or waterlogging are harmful. Climbing cultivars will give economic yields in areas of high rainfall but the dwarf types appear to be more sensitive to high soil moisture levels. Suitable soil types range from light to moderately heavy and to peaty soils with near-neutral pH and good drainage. Common bean is susceptible to salinity.

 The optimum temperature range for growing French beans is 20-25degC, but can be grown in temperatures ranging between 14 and 32degC. Extreme temperatures result in poor flower development and poor pod set. However, French beans mature faster in warmer areas. French beans can be grown between 1000 and 2100 metres above sea level. Rainfed cultivation is possible in areas with well distributed, medium to high annual rainfall (900-1200 mm) but to maintain a continuous production especially during the dry season, irrigation is essential. During the dry season up to 50 mm of water per week is required. This could be applied through furrow or overhead irrigation. French beans grow best on well drained, silty loams to heavy clay soils high in organic matter with pH 5.5-6.5. 

Propagation and planting

Normal propagation is by seed but for special purposes stem cuttings can be rooted easily. French beans, grown for fresh consumption, canning or freezing should be planted at 2-3 week intervals in order to harvest all year round, but main export season for fresh beans is October to May. Hence planting for export at 2-3 week intervals should start mid-August and cease end February. Single rows of 30 x 15 cm (1 seed per planting hole) or double rows 60 x 30 x 10 cm are used. For single rows it is advisable to plant in blocks of 4 single rows separated by a path of 50 cm for ease of management. Seed rate is 50-60 kg per hectare.

 For good pest and disease management avoid planting French beans too close. A spacing of not less than 30 x 15 cm between the rows and within the row is recommended in Kenya. New plantings should be sited up-wind where continuous bean cropping is practiced. Plant maize, cereals or sunflower between French bean fields to minimise the spread of wind-borne diseases such as bean rust.

 Plant population densities are 150,000 – 200,000 plants/ha for dwarf cultivars and half that for climbing types in sole cropping. In intercropping, densities are much lower. For climbing beans, 4-6 seeds are usually sown together in hills spaced 1 m apart. They may also be sown in rows at a spacing of 90-120 x 15-30 cm. Depth of sowing is 3-6 cm. Seed rate depends on seed size and intended plant population densities, up to 120 kg/ha for dwarf beans and 60 kg/ha for climbers in sole cropping. Climbing cultivars require support by stakes or trellis up to 2.5 m in height unless they are intercropped with tall plants such as maize or sorghum – an increasingly common practice in Kenya Rift Valley – the maize or sorghum plants acting as stakes for the bean plants. Avoid planting beans near cowpea, soybean and many other leguminous crops, that may be the source of bean flies.  

Husbandry

Beans are comparatively light feeders and require as a guide line about 25-35 kg P/ ha (equivalent to 1-2 bags of Mijingu rock phosphate/ha) and 75-80 kg K/ha. Like all legumes, beans are able to fix nitrogen from the atmosphere, so do not require nitrogen fertilisation. However a soil conducive to nitrogen fixing with the natural nitrogen fixing bacteria present is preferable. Hard soils with little organic matter will not give good yields of beans, unless organic matter is provided, preferably in the form of good quality compost or well decomposed farmyard manure. For pure stands of beans it is preferable to construct slightly raised beds of maximum 1 metre width in order to limit soil compaction around the bean plants. Application of good compost in the beds will improve yields as it will improve nitrogen fixation. Timely and thorough weeding is essential for French beans.

The first weeding should be done 2-3 weeks after emergence followed by a second weeding 2-3 weeks later. During weeding slight ridging of plants will help bean plants withstand attack of bean flies. Cultivating beans when the soil is wet encourages spread of soil-borne diseases such as anthracnose and fusarium root rot. Shallow tillage is preferred especially in the period before flowering as damage to the roots or the collar of the plant encourages soil borne diseases. Common bean can be rain-fed or irrigated. Irrigation is beneficial in semi-arid regions, with overhead irrigation preferred over flood irrigation. In peasant farming, the crop is seldom manured. Crop rotation is necessary to limit soil borne diseases such as root-knot nematodes and fusarium root rot.Fertilise the soil properly and plant French beans on hills or ridges where root rot could be a problem. Avoid furrow irrigation in areas prone to root rot and root-knot nematodes and fusarium.  

Mulching 

Mulching with straw and cut grasses helps conserve moisture, promote adventitious root development and enhances tolerance to bean fly maggot damage.  

Intercropping

Beans are excellent for intercropping with other food crops, such as maize, potatoes, celery, cucumber and can help supply the other crops with nitrogen to a limited degree. Longer season varieties of beans can fix higher amounts of nitrogen than short season varieties. Intercropping with chives or garlic helps repel aphids (KIOF – personal communication).  

Water management 

A regular water supply is essential for French beans as moisture affects yields, uniformity and quality. Water stress during flowering reduces yields, as does waterlogging. Irrigation in dry spells is recommended as 35 mm per week at planting and 10 days post emergence, followed by 50 mm per week thereafter till end of production.  

Pest and disease prevention with EM or BM 

EM (Effective Microorganisms) and BM (Beneficial Microorganisms) have been shown to prevent many diseases and a few pests in various crops when sprayed on a regular basis. These are commercial products and are readily available in Kenya. It is organically acceptable and quite cheap.  

Harvesting / Storage 

French beans are harvested before the pods are fully-grown. Harvest starts 7-8 weeks after sowing in early cultivars. Pods should be picked every 2-3 days, and the number of pickings is greater in climbing than in bushy cultivars. Dry beans are harvested as soon as a considerable proportion of the pods (roughly 80%) are fully mature and have turned yellow. Some cultivars tend to shatter. Usually entire plants are pulled and further dried till ready for threshing. After threshing the beans are further sun dried to estimated 12 % moisture to avoid storage problems. 

Farmer practices:

Solar drying of bean seeds before storage is essential. Also before storing, mix bean seeds with a) ashes or ash/chilli mixture b) diatomite (commercially available as Kensil Lagging from most hardware shops in Kenya) c) store completely dry seeds in a sealed container such as a metal or plastic bucket with air tight lid, checking regularly that no weevils are developing and closing tightly again.