Thonc

Thonc
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Rosids
Order:	Fabales
Family:	Fabaceae
Subfamily:	Mimosoideae
Tribe:	Mimoseae
Genus:	Leucaena
Species:	L. leucocephala
Binomial name
Leucaena leucocephala (Lam.) de Wit
Synonyms
Leucaena glauca (L.) Benth. Mimosa glauca L. Acacia glauca Willd.

Leucaena leucocephala, also known as Leucaena glauca is a highly branched small tree or shrub, which belongs to the family Mimosaceae. Leucaena is an evergreen, deep rooted plant, which may grow to heights of 3–15 (max. 20) m with a bole diameter of 10–50 cm and a bole hight to 5 m. L. leucocephala has an upright angular branching, which forms a narrow open crown. The leaves are bipinnate with 6-9 pairs. The leaflets are 9-16 mm long and 2-4.5 mm wide. The self-fertile flowers are white or cream-white. 100–180 flowers per head are forming a globular shape. The pods are 13-18 mm long, flat and brown containing a number of seeds. L. leucocephala is used for a variety of purposes, such as firewood, fiber and livestock fodder.

Origin and regions of cultivation

L. leucocephala is probably native to southern Mexico and northern Central America . It is naturalized throughout the West Indies from Bahamas and Cuba to Trinidad and Tobago, and from Texas and Florida to Brazil and Chile. It is also established in Hawaii, Pacific Islands and the Old World tropics.

Yield

Leucaena can produce 50–80 t/ha/year green matter and about 2–20 t/ha/year dry matter. Pods yield can vary between 4.5–7 kg per tree. The tree produces wood yield of about 30-40 m³/ha/year. It is estimated, that an area of 2-5 million ha is cultivated.

Product and use

Leaf tips can be used as a vegetable, pods and seeds can be used as food. It is possible to use the seeds as a coffee substitute. The leaves provide a protein rich fodder, which can be consumed browsed or harvested. Leucaena is as well a good cover and green manure crop and is also of value in land reclamation, erosion control, water conservation, reforestation and soil improvement. The wood is also used in the paper production (fibre) and is a good timber. L. leucocephala is able to produce a gum, which is similar to gum Arabic. The tree produces the gum when stressed by insects or disease. Leucaena is also widely used as fuel or charcoal, because of its very hard and heavy wood. Leucaena wood has 39% the calorific value of fuel oil, charcoal has 72.5%.

Nutritive value

Leucaena is a fodder tree with a high quality. The nutritive value of the leaves is very high and comparable with the fodder crop alfalfa. Leaves can have 55-70% digestability and 20-25% crude protein.

General compositor	Leucaena leucocephala	Alfalfa
Total ash (%)	11	16.6
Total N (%)	4.2	4.3
Crude protein (%)	25.9	26.9
Modified-acid-detergent fibre (%)	20.4	21.7
Calcium (%)	2.36	3.15
Phosphorus (%)	0.23	0.36
b -carotene (mg/kg)	536.0	253.0
Gross energy (kJ/g)	20.1	18.5
Tannin (mg/g)	10.15	0.13

Toxicity: Leucaena leaves and pods contain the toxic amino acid mimosine. The content in edible forage is 4-5%, but the seeds and the youngest leaves can contain about 10%. In non-ruminent animals a high intake of the toxic amino acid can cause loss of hair. In ruminats the mimosine is broken down in the rumen to dihidroxypyridine. A content of more than 40% Leucaena in the diet can also cause symptoms of intoxication in ruminents .

Soil and climate requirements

L. leucocephala is a tropical plant with no frost tolerance but with a high drought tolerance although the yields are lower in dry environments. Waterlogging can reduce the production or can damage young seedlings, but established plants easily survive a short excess of water. The crop requires temperatures about 25-30°C (day) for optimum growth. It grows well at altitudes from 0-1500 m and needs mean annual rainfalls from 650-3000 mm.

Because of its deep root system the tree grows well on different soil types. Leucaena thrives best on deep, well drained, neutral to alkaline clay soils and is not tolerant of soils with low pH and high salinity. For an optimal growth performance Leucaena requires adequate amounts of phosphorus and calcium and does not like high alluminium saturation.

Cultivation

Planting: For planting seed or ‘bar stem’ seedlings are used. The recommended seeding rates are 1-2 kg/ha. The seeds are best sown early in the growing season 2-3 cm deep in rows of 3-10 m. Rainfall should be reliable. The Leucaena seedlings do not cope well with weed competition therefore weed control is needed.

Fertilisation: On infertile tropical soils fertilisation at planting, especially with phosphorus and calcium will be required. To extend the performance of the roots Leucaena needs the vesicular arbuscular mycorrhizae mainly to access the immobile phosphorus. If phosphorus is low up to 100 kg/ha could be applied. Liming will be required in acid soils (pH < 5.0). A lack of calcium in the soil will lower the nodulation.

Harvest

Leucaena can be harvested for fodder at any stage. The yields of the green forage are at peak on 10-12 week cycles. The tree can be cut or grazed by animals. The crop is highly productive and recovers quickly from defoliation and tolerates several decades of cutting and grazing.

Interactions: Pests, diseases, symbionts

Nitrogen fixation: L. leucocephala is a legume and in the symbiosis with Rhizobia bacteria the tree is able to fix about 500 kg nitrogen per ha annually. The nitrogen fixing nodules are found on the small lateral roots near the soil surface.

Pest and diseases: "L. leucocephala is susceptible to the psyllid Heteropsylla cubana, which has caused serious defoliation and mortality in eastern Africa. A Caribbean parasitoid, Psyllaephagus, shows specificity and excellent appetite for H.cubana and hence offers possibilities for biological control. Some varieties are susceptible to gummosis, most likely caused by Fusarium semitectum. Ganoderma lucidum causes root rot in arid and semi-arid regions. Leaf-spot fungus also can cause defoliation under wet conditions. Wild animals avidly consume seedlings."

Invasive properties

Leucaena leucocephala is highly invasive in the arid parts of Taiwan, the Hawaiian Islands, Fiji, and northern Australia. It grows quickly, and forms dense thickets which crowd out any native vegetation. L. leucocephala is considered one of the 100 worst invasive species by the Invasive Species Specialist Group of the IUCN Species Survival Commission.

The plant is also found in California, Arizona, Texas and Florida and is considered weedy or invasive by some authorities.

References

'Leucaena leucocephala is a species of small Mimosoid tree that is native to southern Mexico and northern Central America (Belize and Guatemala). Common names include White Leadtree, Jumbay, and White Popinac. The specific name is derived from the Greek words λευκό, meaning "white", and κέφαλος, meaning "head", referring to its flowers. It is known as Subabool in India. L. leucocephala is used for a variety of purposes, such as firewood, fiber and livestock fodder.

It has been considered for biomass production, as its reported yield of foliage corresponds to a dried mass of 2000–20000 kg/ha/year, and that of wood 30–40 m³/ha/year, with up to twice those amounts in favourable climates. It is also efficient in nitrogen fixation, at more than 500 kg/ha/year. It has a very fast growth rate, young trees reach a height of more than 20 ft in 2–3 years.

During the 1970s and 1980s it was promoted as a "miracle tree" for its multiple uses. It has also been described as a "conflict tree" in that it is both promoted for forage production and spreads like a weed in some places.

This species is susceptible to insect infestations. In the 1980s, there was widespread loss in Southeast Asia due to pest attack by psyllids.. In India, this tree was initially promoted for afforestation due to its fast growing nature. However, it is now considered unsuitable for urban plantation because of its tendency to get uprooted in rain and wind. Eight of every ten uprooted trees in Pune were subabuls.

The seeds contain mimosine, an amino acid known to be toxic to non-ruminant vertebrates (Gutteridge and Shelton 1998). It provides an excellent source of high protein cattle fodder.