Sesbania: Description and uses, climate and soil suitability, planting and management
Description: Sesbania is a fast-growing leguminous shrub or small tree, found both in the humid tropics and in more arid and semi-arid regions. It can easily be grown from seed and nursery seedlings. The tree usually has a main stem but thrives under repeated cuttings and coppices readily, with many branches arising from the main stem below cutting height. Cutting frequencies are generally 3-4 cuts per year but up to 8 cuts are made in some areas.
The leaves are compound, up to 12 cm long, with oblong, tip-notched, narrow leaflets up to 2 cm long. The flowers are pale yellow, speckled maroon or with purple streaks, in flower heads up to 15 cm long each bearing 4-20 flowers.
Uses: Sesbania is often planted on the contour between crops such as maize, beans, cotton, or even other grasses, such as Napier as a soil conservation measure. As a legume it fixes Nitrogen in the soil. It can be used a green manure with leaves composted or used as a mulch. Alternatively, it can be fed to animals, grazed in situ or cut-and-carried to them. It also provides good quality firewood, can be used in Striga (witch weed) control in maize and sorghum crops. It can be used as a windbreak and provides shade and for bee forage
Fodder use: The leaves and tender shoots are used as fodder for ruminants (cows, goats and sheep). The leaves are very palatable and are high in protein so they are an excellent supplement to protein-poor roughage (local grasses, crop residues etc) in ruminant diets. Sesbania is well suited to zero-grazing systems. However, it should be noted that sesbania contains a poisonous saponin which makes it fatal to young chicks, so it should not be included in poultry diets, and should only be fed in limited amounts to other non-ruminants.
Wood use: Sesbania makes good firewood and charcoal because it is fast growing and the wood, although soft, lights easily and is relatively smokeless and hot burning. The wood can be used for a range of purposes including posts, stakes and fences.
Soil conservation and fertility improvement use: Rapid growth, combined with high levels of nitrogen fixation, make sesbania excellent for soil conservation and fertility improvement, particularly as a component of improved fallow systems. It can be planted for soil erosion control on steep slopes at close spacing, in rows 2-6 m apart along the contour, with annual crops such as maize and sorghum between the rows. It has also been used as lightshade for young coffee plants.
Climate: Sesbania grows in cooler, higher elevation regions than most tropical tree legumes. It is naturalised at altitudes as high as 2500 m in East Africa, though at higher and cooler elevations growth rates and yields are reduced. It grows in both semi-arid and sub-humid regions, with annual rainfall ranging from 500 mm to 2000 mm. It prefers areas with alternating wet and dry periods to those with even rainfall distribution throughout the year. Because of its tolerance of both droughts and waterlogging, it is well-adapted to seasonal fluctuations in moisture and to seasonally flooded environments: it is common along streams, swamp banks and in moist and inundated bottomlands. Flooding stimulates the production of floating, adventitious roots.
Soil suitability: Sesbania tolerates slightly acidic soils as well as very alkaline and saline ones, although it is not adapted to soils with high aluminium saturation and pH<4.5. It will grow in marshy areas so is tolerant of waterlogging.
Propagation & establishment: Viability and germination of fresh seeds is high (up to about 95%). The seeds have hard seed coats which need treatment before they can take up moisture and germinate. This is usually done by soaking the seed in either hot or cold water. One method is to put the seeds in a cloth or screen bag and dip them for 30 seconds in water heated to just below boiling point. An alternative is to soak them for 24-48 hours in cold or tepid water. Successfully treated seeds will swell visibly in the water, and the root tips of viable seed will appear within two days. Sesbania can easily be established by direct seeding or as seedlings. Plants can either be raised in a nursery and then transplanted or planted as seed in their final position. Much higher germination and seedling survival rates will be achieved if the plants are raised in a nursery, because the plants can be looked after better, particularly with regard to watering and weeding.
The use of nursery-grown seedlings is normally not necessary with sesbania, except when supplies of seed are limited or establishment from seed is proving difficult. In this case, transplanting seedlings into the field may help.
Seedlings are easily grown either bare-rooted or in containers. The seeds germinate and grow quickly, often up to 10 cm in 20 days, 1 m in six weeks and 2 m in 12 weeks. This rapid growth helps sesbania to overcome weed competition and reduces the amount of weeding needed during establishment.
Management: Sesbania is a very fast-growing species when young. Weeding is necessary, and it can become a weed itself if not well controlled.
Under good conditions, hedgerows of sesbania can produce more than 20 tons/ha/year of dry matter. If cuttings are frequent, more than half of that yield will be leaves. Productivity is greatly influenced by cutting management. It is often highly forked. Low branches and dominant stems can be cut without risk of killing the plants.
Harvesting: Although sesbania does tolerate repeated cutting for fodder, harvesting should not be too frequent, usually 3-4 times per year. It is important not to remove all the leaves, at least 5-25% of the foliage should be left on the plant when pruning. Under favourable conditions, sesbania can produce up to 20 tons of leaf dry matter per year.
Feeding: Sesbania leaves are a good feed supplement for ruminants such as cattle, goats and sheep. The fodder can be fed fresh, wilted or dried. Dried fodder can be stored for times of shortage. The most effective way of feeding sesbania is as a supplement of 15-30% of the total ruminant diet. Because of the high protein content sesbania should not be fed as a sole ration but combined with low protein-high energy roughages such as dry fodder grasses. A low content in sodium, as with many other legumes, indicates a need for mineral supplements.