Leucaena's promising future
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CTA. 1987. Leucaena's promising future. Spore 8. CTA, Wageningen, The Netherlands.
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Leucaena leucocephala offers marvels: high production of fuelwood, fodder and fertilizer resources. But below this beauty lies a serpent: it contains a substance which is harmful to animals. First experiments show that this toxicity can be...
Leucaena leucocephala offers marvels: high production of fuelwood, fodder and fertilizer resources. But below this beauty lies a serpent: it contains a substance which is harmful to animals. First experiments show that this toxicity can be overcome. Leucaena has exceptional merits: a rapid growth rate, unrivalled wood and forage production, and a capacity to fertilize the soil where it grows. But there are some drawbacks: the leaves of leucaena contain 'mimosine', an amino acid that is toxic to animals. This has long prevented the use of leucaena as fodder, but considerable progress is about to be made towards solving this problem thus opening the way for leucaena to play a major role in the tropics. Oaxaca is the name of the Mexican state and city that the Zapotec, an affluent society of the mid 16th century, called 'Uaxin'. The Spanish conquistadors changed it into Oaxaca or 'place where leucaena grows'. Leucaena has since spread far and wide and is still present on its native soil not only in the names of towns and places, but also physically in a great number of varieties. The first leucaena variety that went overseas and spread in tropical areas was the common variety which is a relatively small tree about five meters high, of vigourous and sturdy growth, and which produces seed freely. It first arrived in the Philippines on Spanish ships which left Acapulco exporting mainly pepper, vanilla, cocoa and coffee, but also carrying leucaena leaves as fodder for animals on board. Leucaena seeds spread and germinate all over the islands, demonstrating the qualities of the tree to the local population. Thus the leucaena tree followed the progress of the Spanish conquests. In the 19th century the tree reached the Dutch East Indies, Southeast Asia and finally West Africa But until recently only Leucaena leucocephala, the so-called 'common' variety, was well-known. Research carried out chiefly in Hawaii during the 1 960's has examined over 800 varieties, divided into three main groups: common varietal type, Giant leucaena types and Peruvian types. The 'common' types are principally used by farmers for soil fertilization. Their yield of timber and forage is too low to allow a comparison with other types. Moreover, their sturdiness and resistance apparently also have disadvantages: the plant can turn what is designed to be a controlled cultivation into an overwhelming invasion. The second group includes trees of about twenty meters height, hence the name: 'Giant leucaena'. These types are much appreciated for the considerable quantity of timber they produce. Large plantations of Giant leucaena trees already exist in tropical areas, especially in India, Thailand and the Philippines. The third group contains the so-called Peruvian types. These trees have a height, of around ten metres, produce many low branches and thus make excellent forage trees. The various varieties of leucaena small or giant, whether with good fertilizer forage or wood production qualities, all share common characteristics. Belonging to the family of leguminous plants, leucaena possesses the ability to transform atmospheric nitrogen contained in the soil into components that that can be assimilated by the plant. The Rhizobium bacteria, which are found in the soil, penetrate young roots and multiply around the nodules, enabling leucaena to absorb nitrogen. Thus even on the most marginal soil leucaena grows satisfactorily without nitrogenous fertilizer Leucaena also uses many other resources in its environment, assisted by mycorrhizae, the small soil fungi which can increase the ability of plants to assimilate minerals from the soil. From a physical point of view, nature has been generous with leucaena, in that it endowed it with tap roots which can pierce through layers of hard clay sometimes reaching a depth of two metres in less than a year. The efficiency of its root system enables the tree to absorb water and minerals at depths which are rarely accessible to other plants. Leucaena will not perish even in dry seasons lasting eight or ten months, although its growth may be severely curtailed. But growth will be resumed with the first rainfall. In its native region, Oaxaca in Mexico, growth is slow as severe droughts often destroy practically all plant life. except leucaena It must be remembered, however that to benefit from the production potential of this plant, certain climatic and soil criteria must to be fulfilled. Although leucaena may survive on marginal soils it will perform poorly, if at all, on soils that are either acid or rich in alumina which is unfortunately often the case in the Sahel. On the other hand, leucaena will yield well on fresh, deep soils whether neutral or alkaline, provided that the annual rainfall is between 800 and 2000 mm and that temperatures do not drop below freezing point. Giant leucaena holds two records in timber production. It is the best yearly timber producer, averaging an annual 45 tonnes of dry matter per hectare, and up to 80 tonnes under particularly favourable conditions. This is three to ten times more than the average rate of biomass production. It is also the fastest growing tree and can grow 18 m in four to eight years. Other advantages are that it can be planted very densely, more than 10,000 trees per hectare, given adequate soil and climatic conditions. In Taiwan 10,000 hectares of leucaena have been planted for paper, rayon and timber industries. This tree's rapid growth and the quality of its timber make it an ideal species for profitable and multiple use. In the Philippines, where the authorities are currently setting up an extensive rural electricity network, leucacea will play a major role in providing energy. The Philippine government is counting on leucaena wood to yield up to 4,640 kcal/kg. One hectare planted with leucaena provides the equivalent of 25 to 30 barrels of oil per annum. Nevertheless, researchers from the French Centre for Tropical Forestry Techniques (CTFT) stress that leucaena trees cannot, contrary to what has often been suggested, be counted on to remedy the problem of Africa's desertification. The dry ferruginous or lateritic soil of the Sahel is not favourable for leucaena plantations. But leucaena appears promising for small scale projects of village reforestation in well-selected environments. Leucaena trees are useful not only for industrial and energy production, but also for agriculture. The leucaena is much sought after in many tropical regions for its considerable soil regenerating and fertilizing ability. Litter falling from the trees enriches the soil with large quantities of nitrogen and minerals absorbed by the tree from considerable depths. Studies carried out in Hawaii show that leucaena leaves collected from one hectare contained 44 kg of phosphorus and 187 kg of potassium, as well as calcium and numerous trace elements. It is for this reason that farmers in Hawaii and the Philippines plant leucaena along with grains, mainly maize. A plot of maize, which only yielded 0.66 t/ha/yr doubled its yield in two vears after a hedge of leucaena was planted two or three metres from the crop. On the African continent, in Nigeria for example, leucaena twigs and leaves are being used as a nitrogenous green manure. Associated crops of maize/yam/rice/leucaena hedges have been planted without any additional fertilizer input and in two years yields amounted to three to five tonnes per hectare, i.e. approximately four times the average African maize yield. Animals profit from leucaena leaves which they prefer to those of other forage crops. Veterinarians appreciate their high nutritional value: they are rich in protein, which makes up 25 % to 30 % of leucaena dry matter, with a well-balanced amino-acid, vitamin and mineral content. The Peruvian leucaena types, like the timber types, is not only remarkable for the quality of their production but also for their abundant biomass: in a well-maintained and regularly pruned plantation, production can reach 6 to 18 t/ha/yr of dry matter (leaves and twigs). Lucerne, often regarded as the best forage plant, only produces 8 to 9 t. In dry areas, lucerne only produces 2 to 3 tonnes whereas leucaena remains unaffected by drought as long as its deep roots can reach qroundwater. Many farmers in the tropics have planted Peruvian types of Leucaena at a density of 75,000 to 140,000 plants per hectare for use as forage. More common still is the introduction of leucaena for forage purposes in intensive crop plantations, to take advantage of the fact that leucaena trees have a beneficial effect on the surrounding crops. Others have planted it as hedges along roads or on waste land. Animal weights increase from 300 to 400 kg/ha/yr to 800 kg under optimal conditions. The highest gains can be obtained when leucaena is fed in combination with other forage plants, but the development of leucaena as a forage plant has been undermined by the presence of mimosine in its leaves. This amino-acid can be toxic for certain animals whose digestive system transforms it into DHP (dihydroxypyridine) which affects the thyroid gland. Observers in Australia, Papua New Guinea, and many African countries have found that a diet containing more than 30 % leucaena leaves represents a severe health hazard for cattle resulting in loss of weight, loss of hair, reduced growth, sluggishness and disorders of the reproduction system. Yet elsewhere, in Indonesia, India and Hawaii, animals grow and breed normally while eating a diet entirely composed of leucaena. Australian researchers have found that this phenomenon is due neither to the particular type of leucaena, nor to particular genetic characteristics to be found among cattle of different countries but to the presence in their rumens of a bacterium that breaks down the toxic DHP compound. Research is currently focusing on transferring this bacterium to animals who do not already carry it. The required strain has been isolated in vitro end animals have been inoculated with these bacterial isolates. Inoculation is easy as it can be done naturally within a herd by exposing the animals to saliva left on leaves. The International Livestock Centre for Africa (ILCA) has carried out tests with promising results that indicate that the problem of toxicity may soon be overcome. Another solution to the mimosine problem would be to produce leucaena hybrids with amino-acid free leaves. Australian researchers are currently working in this direction, trying to create a hybrid using two species of plants: Leucaena pulverulenta, which has a low, safe level of mimosine that animals can tolerate but poor leaf production and Leucaena leucocephala. The combination of their characteristics might produce a promising hybrid. Results obtained by researchers indicate that their efforts are meeting with success. Once the toxicity problem of leucaena is overcome, it may turn out to have more hidden advantages than hitherto suspected. Until recently, of the vast array of leucaena species, only Leucaena leucocephala has been the subject of major research and experiments. But forestry experts and researchers are now studying other species more intensively. They are discovering that leucaena species perform well on a wider range of soils than had previously been thought. Leucaena diversifolia and Leucaena shannoni grow on soils that are too acid for Leucaena leucocephala. Leucaena paverulenta is remarkable for its drought tolerance, its adaptability to low temperatures, and its high-quality timber production Leucaena diversifolia and Leucaena esculenta are best suited for high altitudes in tropical areas Is this little Mexican tree, that promises so much and asks for so little, going to turn out to be another of those miracle plants which have been heralded over the past few years ? Unlike the others, which never left the boundaries of research plots, leucaena varieties are already producing satisfactory results in rural areas all over the world. Research will be able to accelerate its distribution and further improve its production. It should not be too difficult to convince farmers of its usefulness. BIBLIOGRAPHY - National Academy (1984) Leucaena: Promising Forage and Tree Crop for the Tropics'. National Academy Press Washington D.C.. U.S A. - Dayadee J. (1984).'lnvestigations on the feeding of sugar cane products and their mode of presentation with leucaena in two breeds of goats in Mauritius'. Scientific Centre. Tropeninstitut, Justus Liebig Universitaet. Giessen. Germany 157 pp. - G.R.E.T (1986) Le Leucaena: mirage ou miracle'. Reseaux Bulletin du Groupe de Recherche et d Echanges Technologiques G. R. E T. Paris. - Haque, I., Jutz, S, Neate, P.J.H. (1986). 'Potentials of forage legumes in farming systems of sub-Saharan Africa'. Proceedings of a workshop held at ILCA, Addis Ababa, 16-19 September 1985, ILCA, 569 PP
SubjectsCROP PRODUCTION AND PROTECTION;
- CTA Spore (English)