Leucaena leucocephala (PROSEA)
Leucaena leucocephala (Lamk) de Wit
- Protologue: Taxon 10: 53 (1961).
- Family: Leguminosae - Mimosoideae
- Chromosome number: 2n= 104
- Leucaena glauca (Willd.) Benth. (1842),
- L. latisiliqua (L.) Gillis (1974).
- Leucaena (En). White leadtree (Am).
- Leucaene, faux mimosa (Fr)
- Indonesia: lamtoro (Javanese), pelending (Sundanese), petai cina (Indonesian)
- Malaysia: petai belalang, petai jawa, ipil-ipil
- Papua New Guinea: lamandro
- Philippines: ipil ipil, elena (Tagalog), palo-maria (Bikol), kariskis (Ilokano)
- Cambodia: khtum té:hs, krâthum' thé:t
- Laos: kathin, kan thin, kh'o:ng ko:ng kha:w
- Thailand: krathin (general), to-bao (southern)
- Vietnam: keo dậu, bo chét.
Origin and geographic distribution
Leucaena evolved in the Guatemalan centre of genetic diversity, as a probable tetraploid hybrid of diploid species in that region. Two major forms are found. The "common" shrubby form grows up to 8 m tall and is evidently indigenous to the Yucatan Peninsula. The arboreal "Salvador" type grows to 16 m and appears to have originated in the regions of El Salvador, Guatemala and Honduras. Both forms were distributed widely throughout Mexico and Central America to northern South America prior to 1500 AD. A single variety of the common form was probably brought by Spanish galleons to the Philippines in the early 1600s, from where it was pantropically distributed in the 19th Century. The Salvador forms are more recent in distribution and are known by names such as "lamtoro gung" in Indonesia, "giant ipil-ipil" in the Philippines and "subabul" in India. Leucaenas are found throughout South-East Asia; on many islands common leucaenas dominate the vegetation on coralline soils.
Leucaena is a very versatile multipurpose tree. In South-East Asia it provides fuelwood, shade, fodder, green manure, mulch, posts, food and often combinations of these products. Leucaena is probably the most widely used species in alley cropping, where it is planted in hedges along contours at intervals of 3-10 m with crops in between. Other auxiliary uses include live fences, fire-breaks, shelter-belts, live support for vines such as pepper, vanilla, yam and passion fruit, and shade trees for coffee and cocoa. Selections low in seed production are preferred for these purposes. Throughout the tropics leucaena provides a major nitrogen-fixing component of lowland wasteland, fallow land and forest, where it is often a primary source of fixed nitrogen in the ecosystem. In Indonesia leucaena is often planted in home gardens.
A dye has been extracted in Central America from the seeds, pods and bark. Research on extraction methods for this potential dye has been conducted in Indonesia.
Foliage is fed to ruminant animals as browse or by cut-and-carry methods and mixed with other green fodders; it is milled as a supplement for poultry feed and pelleted for export. Wood is harvested for fuelwood and used in households and industries such as ceramics; it is also converted into charcoal. Increasing use is made of the wood for posts and props, in chipboard and plywood manufacture, for paper pulp, and for furniture and parquet flooring. In Asia people eat the young green shoots before the leaflets unfold; in the Americas, the green seeds are eaten. In Indonesia the mature seeds are eaten, either raw, cooked or mixed with other ingredients, sometimes after fermentation as a substitute for soyabean, or added to coffee after roasting. Young pods are eaten raw or cooked and serve as a minor, but useful protein and vitamin supplement from the home garden. The dried seeds are widely used for ornamentation.
Production and international trade
Leucaena is a major source of fuelwood and is a primary source of leguminous feed in large regions of Indonesia and the Philippines. Most production is on communal lands or small farms. Attempts to commercialize production on large fuelwood plantations (1000 ha or more) for electricity production in the Philippines have not been a great success.
Leucaena leaf meal is milled, pelleted and shipped internationally in a very variable annual volume, largely to Japan and Europe. Demand is estimated to be up to 1 million t/year, far exceeding production, with world prices similar to those for lucerne pellets or hay. Prices of fodder and wood vary widely in Asia.
Prunings of leucaena applied as green manure decompose rapidly. In litterbag experiments in Nigeria using dried prunings, about 50% of the prunings had decomposed after 20 days and 80% after 40 days. Analyses in Ivory Coast gave a half-life time of 31 days. Chemical analyses of prunings of leucaena grown on alfisols in Nigeria indicated per 100 g dry matter: N 3.3-3.5 g, P 0.09-0.25 g, K 2.5-2.8 g, Ca 1.3-1.6 g, Mg 0.2-0.4 g, lignin 13.4 g, cellulose 21.1 g, hemicellulose 13.5 g, polyphenols 5.0 g and a C/N ratio of 45.5. The average composition of the leaves per 100 g dry matter based on various sources is: N 2.9-4.3 g, P 0.1-0.3 g, K 1.5-2.5 g, Ca 0.5-2.2 g, Mg 0.2-0.4 g.
Leucaena foliage is noted for its good digestibility and high protein value. Feeding leucaena generally improves the total intake of dry matter and of digestible nutrients. Typical values for "browse fraction" of foliage include 55-70% digestibility, 3-4% N, 6% ether extract, 6-10% ash, 30-50% N-free extract (neutral detergent fibre 20%), 1.5-2.5% tannins, 0.8-1.87% Ca and 0.23-0.27% P. However, the Na levels are invariably low: 0.01-0.05%. The seeds and leaves contain galactomannan gums that block protein extraction and possibly protein utilization by animals; they may potentially have useful biomedical properties. Leucaena contains the toxic amino acid mimosine which has antimitotic and depilatory effects on animals. It occurs in high concentrations in the growing tips (8-12%), young leaves (4-6%) and young pods and seeds (4-5%). For this reason leucaena leaf cannot safely be included in rations for non-ruminants at a level greater than 5% on a dry matter basis. In ruminants the ingested mimosine is converted to the goitrogenic toxin 3-hydroxy-4(1H)-pyridone (DHP) by plant enzymes and rumen bacteria. In most countries, including Indonesia and the Philippines, rumen bacterium (Synergistes jonesii), can completely detoxify mimosine and DHP.
Leucaena wood has an exceptionally high density and energy value for a very fast-growing tree and makes excellent firewood and charcoal. The wood has a density of 500-600 kg/m3and a moisture content which varies between 30-50% depending on maturity. Energy values (bone-dry) of wood average 19 250 kJ/kg, of charcoal 48 400 kJ/kg. The bark is thin. The wood turns well, matures to a golden-brown colour and is hard enough for flooring. It is perishable outdoors, but accepts preservatives well. It does not resist termites. Pulp yields are high (50-52%), lignin levels low, fibres short (1.1-1.3 mm); paper quality generally is considered excellent.
The trees occasionally exude a gum very similar to gum arabic, with similar uses and properties; sterile hybrids, especially L. leucocephala × L. esculenta Benth., exude copiously.
- Shrub or tree up to 20 m tall, forked when shrubby or after coppicing, with greyish bark and prominent lenticels; branchlets terete, at the top densely grey pubescent.
- Leaves bipinnate with 3-10 pairs of pinnae, variable in length up to 35 cm, with an orbicular gland (up to 5 mm) below the proximal pair of pinnae; stipules small; pinnae about 10 cm long; leaflets opposite, 5-20 pairs per pinna, linear or linear-oblong, (6-)8-16(-21) mm × 1-2(-5) mm, base slightly asymmetrically cuneate, apex acute or short-apiculate, both surfaces glabrous, margins ciliate, lower surface glaucous.
- Inflorescence consisting of pedunculate glomerules aggregated up to 3 in leaf axils or in terminal raceme; peduncle 2-5 cm long, densely grey pubescent; glomerule 2-5 cm in diameter, white; flowers numerous, in globose heads with a diameter of 2-5 cm, white.
- Calyx tubular-campanulate, about 2.5 mm long, puberulous at apex, teeth triangular, acute; petals spathulate, 4.5-5 mm long, puberulous; stamens 10, free, creamy-white to greenish-white; filaments 8-10 mm long; anthers pilose, dehiscing at dawn; pistil 10 mm long, ovary stipitate, velutinous at apex.
- Pod membranous, straight, dehiscent, 14-26 cm × 1.5-2 cm, pendant, brown at maturity, 15-30-seeded.
- Seeds held obliquely in pod, narrowly ovoid, compressed, 6-10 mm × 3-4.5 mm, brown, obtuse at apex, cuneate at base; areole oblong, open towards hilum.
Growth and development
Leucaena establishes fairly slowly, particularly in competition with weeds and when grown on soils which are acid or low in nutrients. It sets pods cyclically every 6-8 months if moisture is sufficient, and this is associated with suppression of vegetative growth during fruiting. Arboreal cultivars have been selected for lower flowering rate. Fruits ripen in 10-15 weeks. The flowers are self-fertile and most seed results from self-pollination (this is not true for related species with 2 n = 52 or 2 n = 56). Seeds have a hard seedcoat and survive in the soil for a long time. Seedlings produce a single strong taproot in the first month. Nodulation occurs generally within 2 months in the top 20 cm of soil. Rooting is generally deep, making it a good wind-break and companion tree. Rates of growth usually increase after 3 months, continuing linearly for 3-4 years. Mature trees may reach a stem diameter at breast height of 40 cm. Leucaena coppices well. Coppiced stems sprout 5-15 branches, depending on diameter of the cut surface, and 1-4 stems dominate after a year of regrowth. New stems can grow very rapidly and may reach a height of 10 m in 2 years. Individual leaves persist from 4-6 months. They fold at night or under stress.
Other botanical information
The common and giant forms of L. leucocephala are distinguished taxonomically as L. leucocephala var. leucocephala (common form, shrubby, less than 5 m tall, small plant parts, pubescent shoot tips, seeding profusely) and L. leucocephala var. glabrata Rose (giant form, arboreal, up to 20 m tall, with large plant parts, glabrous shoots). Intermediate types, combining vigorous growth (up to 10 m tall) and large leaves of good fodder quality with extensive, low branching are referred to as the "Peru" form. The giant or "glabrata" form gives the highest yields of fodder with infrequent cutting, often outperforming the common form by 100%. The best known cultivars in South-East Asia are "K8", "K29", "K67" and "K636" (now "Tarramba") which resulted from research work in Hawaii, and the cultivar "Cunningham" from Australia. Psyllid-resistant cultivars "KX2" and "KX3" are interspecific hybrids and are becoming popular in Asia.
Leucaena is found up to 1000 m elevation, but new hybrids such as "KX3" greatly extend this range to cooler climates. Leucaena generally requires annual rainfall of 650-1500 mm, but can be found in drier and wetter locations. It thrives under irrigation regimes similar to those used for crops such as maize (i.e. > 1200 mm/year). For optimal growth leucaena requires warm conditions: mean annual temperature ranging from 20-26 °C, maximum temperature range of the hottest month 24-32 °C and minimum temperature range of the coldest month 16-24 °C. Some cultivars of leucaena are sensitive for even light frost, which causes defoliation; others tolerate frost well, provided it is not too severe or too frequent. Severe frost kills all above-ground parts, but below-ground parts survive and plants will regrow vigorously. Some hybrids e.g. with L. retusa Benth. are more frost resistant. Growth of leucaena is highly light- and temperature-dependent. Daily dry matter increments in Hawaii ranged from 13.8 kg/ha in winter (average temperature of 21 °C and irradiation of 15 MJ/m2) to 26.9 kg/ha in summer (average temperature 26 °C and irradiation of 23 MJ/m2).
Leucaena favours deep, well-drained soils with pH > 5, and has a low tolerance to soluble Al. It performs optimally on calcareous soils, but can be found on saline soils and on alkaline soils up to pH 8. Leucaena is not suited to acid soils with pH(H2O) < 4.8 or to waterlogged conditions. Adequate levels of available phosphorus are needed.
Propagation and planting
Leucaena can be propagated by directly sowing seed or by transplanting seedlings. Seed must be scarified to improve germination, usually by placing it in water at 80 °C for 3 minutes followed by removal and then allowing it to cool. Inoculation using peat cultures of improved rhizobia strains such as CB3060 (TAL 1145) or CB81 is important for early nodulation and growth. In the absence of peat inoculants the soil from under well-established stands of leucaena can be used as inoculant to promote early establishment. This may also promote early infection by mycorrhiza. It is important not to sow the seed more than 2 cm below the soil surface. Where possible, weeds should be controlled either by slashing or by appropriate chemicals, as early growth is severely reduced by competition. In alley cropping, hedges are planted 4-10 m apart with an intra-row spacing of 0.25-1 m, depending on the pruning regime adopted and the associated crops. Spacing is an effective management tool, as it affects diameter growth more than growth in height. Maximum wood yields in 4-year rotations are obtained with 10 000-20 000 trees/ha. For household fuelwood production leucaena is planted at very high densities of up to 40 000 trees/ha and grown in a 3-year cycle, giving stems with a diameter of about 3.5 cm; for timber and fibre production stands are thinned 2-3 years after planting to 1-2 m × 2 m.
For forage, seeds are usually sown in rows 1-5 m apart with a seeding rate of 5-7 kg/ha, using fertilizer where necessary to correct known soil deficiencies. In cut-and-carry systems, closer plant spacing gives higher yields of leucaena. However, in grazed situations the wider row spacings of 2-5 m are more appropriate to enable grass to grow between the rows. Leucaena can also be established by raising seedlings in the nursery in long narrow containers (3 cm × 15 cm) which accommodate the strong taproot without coiling. Transplanting is done when seedlings are 3-5 months old, preferably after a month in the full sun. Bare-rooted seedlings can be transplanted effectively if shoot and roots are topped. Although weed competition strongly reduces early growth, leucaena is often able to survive because of its ability to tolerate some shade, thereby eventually growing above the weed canopy, provided the area is not closely grazed or mown.
Leucaena is a suitable tree for alley cropping provided adequate moisture is available and soil acidity and Al content are not limiting. In long-term alley-cropping experiments in Nigeria and Zaire with leucaena and maize, maize yields in the alley-cropped plots gradually increased over time, but could not be maintained in the plots receiving only chemical fertilizer or manure. In an experiment in Kenya half of the leucaena prunings could be removed for fodder without a significant reduction in maize yield, provided the manure of the animals was returned to the field.
Plants in established hedges are pruned to 25-50 cm at the planting of the associated crop. Subsequent pruning intervals of 6 weeks during the cropping season have given good results. Hedges could be maintained under this system even where 2 crops of maize were grown per year. In India root pruning using a local plough increased yield of the associated sorghum by about 25%. However, information on how to manage the balance of competition between leucaena and the associated crop is still incomplete.
Leucaena has been tested as a live support for yam in a trial in Ivory Coast. In spite of regular pruning it reduced yam tuber yields considerably more than live supports of Flemingia macrophylla (Willd.) Merrill or Gliricidia sepium (Jacq.) Kunth ex Walp. Its stronger branching, denser shade and denser root system made leucaena more competitive than the other species.
For grazing, leucaena can be grown with many grasses. Pangola grass (Digitaria eriantha Steudel), guinea grass (Panicum maximum Jacq.), signal grass (Brachiaria decumbens Stapf) and Sabi grass (Urochloa mosambicensis (Hack.) Dandy) are suitable in the tropics. In the subtropics, Rhodes grass (Chloris gayana Kunth) and setaria (Setaria sphacelata (Schumach.) Stapf & Hubbard ex M.B. Jones) are suitable companion grasses. Leucaena is very palatable and stands can easily be weakened by heavy continuous grazing. Several rotational grazing strategies have been successful, including a simple 2 paddock system of 4 weeks grazing / 4 weeks rest and a 4 paddock system of 2 weeks grazing / 6 weeks rest. The main principle is to move the animals before they graze leucaena regrowth. When adequate leucaena is available, cattle should be capable of weight gains of about 1 kg/head per day provided the Na level in the diet is adequate.
Diseases and pests
There are few diseases of leucaena. Seedling rots such as Phytophthora drechsleri and Fusarium semitectum attack primarily under waterlogged conditions. The root pathogen Pirex subvenosus causes dieback on heavy textured soils in some areas (e.g. on some irrigation areas in north-western Australia). Until the mid-1980s leucaena was relatively free of serious diseases and pests. However, since then devastating effects of the leucaena psyllid (Heteropsylla cubana), a tiny, jumping plant louse have been experienced in many areas where leucaena is grown. Psyllid damage is rarely seen in leucaena's centre of origin in South and Central America, and damage caused by the psyllid has decreased with time in other areas. Populations of this insect fluctuate through the season and can reduce yield by over 50%. Attempts to use predatory and parasitic insects for control have met with varying success. The pest now limits the further development of forage leucaena in some areas. Other leucaena species show resistance to psyllids, and have been used in the breeding of resistant hybrids "KX1", "KX2" and "KX3".
Attacks of soft scale (Cocus longulus) and an associated sooty mould can be serious on plants allowed to grow tall. Seed crops can also suffer yield reduction through larvae of the moth Ithome lassula attacking the inflorescences and young pods. In some areas, notably Central America and more recently in Australia, bruchid beetles can seriously reduce or destroy seed crops.
Seedlings can suffer attack from cutworms and termites, but, provided there is an adequate stand density, subsequent production is usually not reduced.
In alley-cropping systems leucaena is generally cut back to 25-50 cm. Pruning is repeated every 6-8 weeks. In cut-and-carry fodder systems the plants are cut back to 0.5-1.0 m height every 6-8 weeks during the growing season and fed fresh to ruminants. In some of the Indonesian islands (particularly Timor), fresh leucaena may form a large part of the diet of tethered animals intended for slaughter. Banana pseudostems are also fed, to provide water. Such a diet is grossly inadequate in Na, and salt supplementation is required for good production.
Wood harvest periods range very widely, from 1-8 years, depending on size of desired product and harvesting equipment. Matchets are commonly used in Asia, but bandsaws and chainsaws can also be used.
Yields of green manure and forage vary with soil fertility, rainfall, altitude and cutting management, from 1-15 t/ha of dry matter per year. Total yields are reduced by frequent cutting, though leaf yield per day may vary little between cutting intervals of 6, 8 or 12 weeks. Highest yields are obtained under wet tropical lowland conditions on deep well-drained, neutral to alkaline soils. Although leucaena is drought tolerant, yields in the dry season are low unless the plants have access to groundwater or are irrigated.
Wood yields compare favourably with the best tropical trees, with annual height increments of 3-5 m and annual wood increments of 20-60 m3for the arboreal cultivars.
Handling after harvest
Fodder is commonly fed fresh or provided as a browse. Sun-drying is practised for leaf pelleting and marketing, often by placing branches over a trellis or on asphalt to allow the leaflets to drop. Wood handling is similar to that of other fuelwood or pulpwood species.
Three major collections are held at the University of Hawaii (Honolulu, United States), the Australian Tropical Forages Genetic Resource Centre (CSIRO, Australia), and the Oxford Forestry Institute (United Kingdom). They comprise all 17 Leucaena species and total 2000 accessions derived largely from expeditions to Mexico, Central and South America. They are identified by K numbers (Hawaii), CPI numbers (Australia) or OFI numbers (United Kingdom). Naturalized populations of leucaena in Asia show limited genetic variation and are not recommended for production as they are outyielded by improved cultivars.
Breeding of leucaena is in progress at the University of Hawaii and the University of Queensland, Australia, with the key objective of incorporating psyllid resistance and cold-tolerance from other Leucaena species (primarily L. diversifolia Benth. and L. pallida Britton & Rose) into agronomically desirable forms of L. leucocephala.
Over the last 2 decades leucaena has been one of the most promising multipurpose legumes in South-East Asia. The arrival in 1984 to 1986 of the psyllids curbed the previous enthusiasm, but partial control of the problem now occurs with natural or introduced predators. The prospect of new lines or hybrids more tolerant or resistant to the psyllid has renewed interest in this and related species. Newly-bred cultivars widen the climatic range of leucaena to the highlands and subtropical regions, and some of the new hybrids (e.g. "KX3") are very cold-tolerant. Improved bole shape ("K636"), psyllid resistance ("KX1", "KX2"), low mimosine content ("KX3") and increased vegetative vigour are among other advances in breeding.
Improved alley-cropping methods of managing leucaena have been developed in Africa, Indonesia, the Philippines and Central America (Haiti). These are expected to improve crop yields in association with leucaena and aid in the stabilization of land-use systems and of fragile tropical soils.
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R.J. Jones, J.L. Brewbaker & C.T. Sorensson