1894

4: Forages

Leucaena leucocephala (Lamk) de Wit

Taxon 10: 53 (1961).

LEGUMINOSAE

2n = 104

Leucaena glauca (Willd.) Benth. (1842), Leucaena latisiliqua (L.) Gillis (1974).

Leucaena (En). Indonesia: lamtoro, klandingan (Javanese), petai cina (Indonesian). Malaysia: petai belalang, ipil-ipil. Papua New Guinea: kunai. Philippines: ipil ipil, elena (Tagalog), palo-maria (Bikol), kariskis (Ilokano). Cambodia: ka-thum' théét. Laos: kathin, kh'oonz koong khaaw. Thailand: krathin (general), to-bao (southern). Vietnam: keo dâu, bo chét.

Leucaena evolved in the Guatemalan centre of origin, 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 Salvador, Guatemala and Honduras. Both forms were distributed widely throughout Mexico and Central America to northern South America prior to 1500 AD. The common form was probably brought by Spanish galleons to the Philippines in the early 1600s, from whence 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.

Leucaenas are versatile multipurpose trees. In South-East Asia they usually provide a combination of fodder, fuelwood, posts, shade, food and green manure. Foliage is fed to ruminant animals as browse or by cut-and-carry methods, or is milled for poultry and pelleted for export. Wood is cut for home fuelwood and used in industries such as ceramics or electrical power generation; it is also converted into charcoal. Increasing use is made of the wood for posts and props, in chipboard and plywood, for paper pulp, and for furniture and parquet flooring. In Asia people eat the young green shoots prior to leaflet unfolding, but in the Americas the green seeds are eaten. Alley cropping involves planting leucaena hedges on contours at intervals of 3—6 m with crops in between. Hedges provide a high-nitrogen green manure, protect against soil erosion and can be harvested for fodder or wood.
Other uses include living fences, support systems for vines like pepper and passionfruit, shade trees for coffee and cocoa and ornamental plantings. Throughout the tropics leucaenas provide a major nitrogen-fixing component of lowland forests, notably on wasteland where they are often a primary source of fixed nitrogen in the ecosystem. The dried seeds are widely used for ornamentation and household items.

Leucaena leaf meal is milled, pelleted and shipped internationally in a very variable annual volume, largely to Japan and Europe for animal feed. Demand is estimated to be up to 1 million t/year, far exceeding production, with world prices similar to those for alfalfa pellets or hay. Prices in local markets in Asia vary widely for both fodder and wood. However, leucaena is the primary leguminous feed in large regions of Indonesia and the Philippines, and the trees are a major source of fuelwood in these and other countries. Most production is on communal lands or small farms. Attempts to commercialize production on large plantations (1000 ha or more) for dendrothermal energy in the Philippines have not been a great success.

Leucaena foliage is noted for its good digestibility and high protein values. 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 its utilization by animals; they may potentially have useful biomedical properties.
Leucaena also 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 above 5% on a DM basis. The mimosine ingested by ruminants is converted to 3-hydroxy-4(IH)-pyridone(DHP) by plant enzymes and rumen bacteria. The DHP is goitrogenic and, if not degraded, can result in low serum thyroxine levels, ulceration of the oesophagus and reticulo-rumen, excessive salivation, poor appetite and low liveweight gains especially when the diet contains more than 30% leucaena. Fertility may also be reduced. In most countries in South and Central America, the United States, Mexico, Indonesia, the Philippines and India, rumen microbes can completely detoxify mimosine and DHP. Isolation of specific bacteria has enabled the DHP-degrading bacteria to be transferred successfully to Australia, Africa and China with beneficial effects for ruminants on diets containing much leucaena.
The trees occasionally exude a gum very similar to gum arabic, with similar uses and properties; sterile hybrids exude copiously.
Leucaena produces a medium hardwood with specific gravity between 0.5 and 0.6 and a moisture content which varies between 30—50% depending on maturity. Heating values (bone-dry) average 19 250 kJ/kg. Bark is thin. The wood turns well, matures to a golden-brown colour and is hard enough for flooring. It accepts preservatives well but 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.

Shrub or tree up to 18 m tall, forked when shrubby or after coppicing, with greyish bark and prominent lenticels. Leaves bipinnate with 4—9 pairs of pinnae, variable in length up to 35 cm, with a large gland (up to 5 mm) at base of petiole, leaflets 11—22 pairs per pinna, 8—16 mm x 1—2 mm, acute. Flowers numerous, in globose heads with a diameter of 2—5 cm, white, calyx ca. 2.5 mm, corolla ca. 5 mm, stamens (10 per flower) and pistil 10 mm long, anthers pilose, dehiscing at dawn. Pod 14—26 cm x 1.5—2 cm, pendant, brown at maturity. Seeds 18—22 per pod, 6—10 mm long, brown.

Leucaena 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 greatly reduced flowering. 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 2n = 52 or 2n = 56). Seeds have a hard seed-coat and survive for a long time in the soil. Seedlings produce a single strong taproot in the first month, followed later by feeder roots. Nodulation is often slow, but occurs within 2 months. Rates of growth usually increase after 3 months, continuing linearly for 3—4 years. Coppiced stems sprout 5—15 branches, depending on diameter of the cut surface, and 1—4 stems dominate after a year of regrowth. Individual leaves persist from 4—6 months and fold at night or under stress.

The common and giant forms of Leucaena leucocephala are distinguished taxonomically as Leucaena leucocephala var. leucocephala (common form, shrubby, small plant parts, pubescent shoot tips) and Leucaena leucocephala var. glabrata Rose (giant form, arboreal, with large plant parts, glabrous shoots). Intermediate types are referred to as the 'Peru' form. The giant or 'glabrata' form gives the highest yields of fodder with infrequent cutting. The best known cultivars in South-East Asia are 'K8', 'K29', 'K67', 'K156' (a cultivar of Leucaena diversifolia (Schlecht.) Benth.) and 'K636' which resulted from research work in Hawaii, and the cultivar 'Cunningham' in Australia. Psyllid-resistant cultivars 'KX1', 'KX2' and 'KX3' are interspecific hybrids and are becoming popular in Asia.

Leucaena is found from lowlands 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 sites depending on competitive vegetation. It thrives under irrigation regimes similar to those used for crops like maize (i.e. > 1200 mm/year). Leucaena favours soils with pH > 5, and has a low tolerance of free Al. It performs best on coralline and other 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) < 4.5 or to waterlogged conditions.

Leucaena establishes fairly slowly, particularly in competition with weed species and when grown on soils which are acid or low in nutrient status. For best results, leucaena should be planted on well-drained soils with a pH above 5.5 and with a deep soil profile. This is particularly important if productivity during the dry season is required.
Seeds must be scarified to improve germination, usually by placing the seeds for 3 minutes in water at 80°C and then allowing them to cool. Inoculation using peat cultures of improved strains such as CB81 or CB3060 (TAL 1145) is important for early nodulation and growth. In the absence of peat inoculants, the soil under well-established stands of leucaena could be used to promote early establishment. This may also promote early infection by mycorrhiza. It is important not to sow the seed too deeply (below 2 cm) and, where possible, competing species should be controlled either by slashing or by appropriate chemicals. 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 but in grazed situations the wider row spacings of 2—5 m are more appropriate to enable the grass to grow between the rows to prevent soil 'plugging' during wet weather. Leucaena can also be established by raising seedlings in the nursery in long narrow containers (3 cm x 15 cm), accommodating 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.
Establishment is often more successful on areas which were previously under grassland than on areas which were previously cropped and therefore contain large numbers of weed seeds. Despite weed competition, leucaena is often able to survive because of its ability to tolerate shade, thereby eventually growing above the weed canopy, provided the area is not closely grazed or mown.

For grazing situations, leucaena can be grown with many grasses. In the subtropics, rhodes grass (Chloris gayana Kunth) and setaria (Setaria sphacelata (Schumach.) Stapf & Hubbard ex M.B. Moss) have been suitable companion 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.
Leucaena is very palatable and stands can be easily 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 new leucaena regrowth. Specific paddocks of leucaena can also be used in conjunction with areas of native pasture, using the rotational principle to prevent overgrazing of the palatable leucaena. 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 of leucaena are few and include seedling rots such as Phytophthora drechsleri and Fusarium semitectum that attack primarily under waterlogged conditions. Until the mid-1980s leucaena was relatively free of serious diseases and pests. However, devastating effects of the leucaena psyllid (Heteropsylla cubana), a small aphid-like sucking insect, have been experienced in many areas where leucaena is grown for fodder. 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 these insects fluctuate through the season and can cause losses of over 50% in yield. Attempts to use predatory and parasitic insects for control have been variably successful. This pest is now limiting the further development of leucaena for forage in some areas. Other leucaena species show resistance to psyllids, and have been used in the breeding of resistant hybrids 'KX1', 'KX2' and 'KX3'.
On plants allowed to grow tall, attacks of soft scale (Cocus longulus) and an associated sooty mould can be serious. Seed crops can also suffer yield reduction through attacks on the inflorescences and young pods from the larvae of the moth Ithome lassula. In some areas, notably Central America, 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 cut-and-carry 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 many situations, leucaena is fed as a protein supplement to grass or cereal straws. Sometimes the feeding of leucaena improves the intake of the basal diet, but generally it improves the total intake of DM, protein and digestible nutrients. The extent of the improvement depends on the amount of leucaena that is fed.
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 deficient 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. Machetes are commonly used in Asia, but bandsaws and chainsaws can also be used.

Yields of forage vary with soil fertility, rainfall, altitude and cutting management from 1—15 t/ha of DM per year. Total yields are reduced by frequent cutting, though leaf yield per day may vary little between cutting at 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 sub-surface water or are irrigated.
Wood yields compare favourably with the best tropical trees, with height increments of 3—5 m/year and wood increments of 20—60 m³/year for arboreal varieties.

Fodder is commonly fed fresh or provided as a browse. Sun-drying is practised for leaf pelleting and marketing, often by placing branches over trelliswork or on asphalt to allow the leaflets to drop. Wood handling is similar to that of other fuelwood or pulpwood species.

Two major collections are held at NFTA (Hawaii) and ATFGRC (CSIRO, Australia). They comprise all 14 Leucaena species and total 1800 accessions derived largely from 7 expeditions to Mexico and Central or South America. They are identified by K numbers (Hawaii) or CPI numbers (Australia). Naturalized populations of leucaena in Asia show limited genetic variation and are not recommended for production as they are out-yielded by improved cultivars.

Breeding of leucaena is in progress at NFTA (Hawaii) and CSIRO (Australia). The key objective is to incorporate psyllid resistance from other Leucaena species (primarily Leucaena diversifolia and Leucaena pallida Britton & Rose) into agronomically desirable forms of Leucaena leucocephala.

Over the last 2 decades, leucaena has been one of the most promising forage legumes in South-East Asia. The arrival of the psyllids has curbed the previous enthusiasm. However, partial control of the problem with natural or introduced predators, and the prospect of new lines or hybrids more tolerant or resistant to the psyllid, have renewed interest in this and related species.
Newly-bred cultivars widen the climatic range of leucaena to the highlands and subtropical regions, with great cold tolerance characterizing some new hybrids ('KX3'). 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 and Indonesia. These are expected to improve crop yields in association with leucaena and aid in the stabilization of shifting systems of agriculture and of fragile tropical soils.

Brewbaker, J.L., 1987. Species in the genus Leucaena. Leucaena Research Reports 7: 6-20.
Brewbaker, J.L., 1987. Leucaena: A genus of multipurpose trees for tropical agroforestry. In: Steppler, H.A., Nair, P.K.R. (Editors): Agroforestry; a decade of development. ICRAF, Nairobi, Kenya. pp. 289-323.
Hill, G.D., 1971. Leucaena leucocephala for pastures in the tropics. Herbage Abstracts 41: 111-119.
International Development and Research Centre, 1983. Leucaena research in the Asia-Pacific region. Proceedings of Singapore Workshop, Nitrogen Fixing Tree Association (NFTA) & IDRC, Ottawa, Canada. 192 pp.
Jones, R.J., 1979. The value of Leucaena leucocephala as a feed for ruminants in the tropics. World Animal Review 31: 13-22.
Jones, R.J., 1985. Leucaena toxicity and the ruminal degradation of mimosine. In: Seawright, A.A., Hegarty, M.P., James, L.F. & Keeler, R.F. (Editors): Plant toxicology. Proceedings of the Australia-U.S.A. Poisonous Plants Symposium, Brisbane, Australia. May 14-18, 1984. pp. 111-119.
Jones, R.J. & Megarrity, R.G., 1986. Successful transfer of DHP-degrading bacteria from Hawaiian goats to Australian ruminants to overcome the toxicity of Leucaena. Australian Veterinary Journal 63: 69-78.
Oakes, A.J., 1968. Leucaena leucocephala; description, culture, utilization. Advancing Frontiers of Plant Science (India) 10: 1-114.
Pound, B. & Martinez Cairo, L., 1983. Leucaena, its cultivation and use. Overseas Development Administration, London. 287 pp.
Takahashi, M. & Ripperton, J.C., 1949. Koa Haole (Leucaena glauca). Its establishment, culture and utilisation as a forage crop. University of Hawaii Agricultural Experiment Station Bulletin 100. pp. 1-56.

R.J. Jones, J.L. Brewbaker & C.T. Sorensson

Jones, R.J., Brewbaker, J.L. & Sorensson, C.T., 1992. Leucaena leucocephala (Lamk) de Wit. In: Mannetje, L.'t and Jones, R.M. (Editors): Plant Resources of South-East Asia No 4: Forages. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea