9. Nuts: multi-purpose and profitable
SPORE, 36, 1992, p.5
Most nuts are highly nutritious and some have a high sale value. Cashew and macadamia are much in demand for export while other kinds of nuts are produced more locally and may be unknown outside a particular region. Some of these also have the potential to become useful, productive and profitable crops elsewhere.
Typically, most nut species are moderate to large trees suitable for planting singly in gardens, hedgerows, orchards or as part of agroforestry. As well as cropping, they provide shade and stabilize the soil. Some have very deep roots and remain productive under surprisingly arid conditions.
The cashew (Anacardium occidentale) is the most widely grown nut, excepting coconut and oilpalm which are in a different crop category. It originated in the American tropics from Mexico to Brazil, but has long since spread successfully to many lowland tropical areas in Africa and Asia. The largest African producers of cashews are Mozambique and Tanzania with smaller amounts being produced in Kenya, Madagascar, Malawi, Nigeria and Senegal. But there is much greater potential for this crop. The nuts have a high export value, while the cashew apple can be consumed fresh or dried. The shell of the nut yields phenol-containing oils which are used for preserving, waterproofing and, after distillation, for brake-linings, inks and cements.
The cashew grows on relatively dry and infertile soils but requires high temperatures and no rainfall during flowering and harvesting in order to produce optimum yields. Since harvesting is by hand, plentiful, inexpensive labour is essential. This is true of most nuts and fruits and may be seen as advantageous since harvesting provides an income opportunity in rural areas. Processing is necessary to remove the cashew shell nut liquid which can blister human skin. In the past, East African output was shipped to India for processing but now processing plants are being built in Kenya, Mozambique and Tanzania.
The macadamia (Macadamia integrifolia) is a more recent arrival in Africa, having originated in Australia. Macadamias require a frost-free sub-tropical climate with at least 125 cm of well-distributed rainfall per year. They will grow on a wide variety of soils if drainage is adequate. However, wind is a hazard: the wood is brittle, and where there are strong winds plantations must be protected by windbreaks.
The kola nut (Cola nitida), dika nut (Irvingia gabonensis) and njansan (Ricinodendron africanum) all grow in wet forest regions but the kola is the most widely grown; it is widely traded as a bitter chewing stimulant. The kola is still mainly harvested from forests but is increasingly planted in orchards, in cocoa plantations and among coffee.
The tree is slow growing and only comes into full production in about the twentieth year.
The dika nut matures in seven years and although exploitation is still limited to self-planted trees the dika seems suitable for planting in hedges, wooded areas, mixed orchards and pure groves. The fruit looks like a small mango and can be eaten in the same way but it is the kernels that are most esteemed: when heated they yield a thick oil. The kernels are also ground to make a paste for thickening stews in the same way as the groundnut and njansan. Njansans are tall trees producing fruits with kernels that have several culinary uses. They can be eaten grilled or ground into a paste and oil can be extracted from the kernels. Most exploitation is from the wild but trees are now being planted deliberately in some regions.
The mongongo nut (Ricinodendron rauteanenii) from the Kalahari and the ye-eb (Codeauxin edulis) from Somalia are staples of local diet in very arid regions and the practicality of these species being planted as desert orchards in their countries of origin and elsewhere is being investigated. Germination and seedling health remain problematic.
An arid land species which is much more widely exploited, although again there have been difficulties, domesticating it as orchard plantings, is the shea butter tree (Butyrospermum parkii). The shea nut is used throughout the Sahel for food and as a raw material for cosmetics and medicines. It has considerable economic potential.
At a time when tree planting is being promoted widely in most parts of the tropics there is ample evidence to suggest that one or more species of nuts may be suitable candidates for selection. Perennial species require little cultural attention and most nut species appear to thrive on poor soils with a little or no demand for agrochemical inputs. They deserve more attention than they have received in the past.
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Review, Africa, Asia, Latin America, drumstick tree, horseradish, spinach tree, multipurpose tree, food, seed oil, cosmetic industry, water purification, project, GTZ
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