Leucaena leucocephala, formerly known as L. glauca, is a thorn-less long-lived shrub or tree that produces highly digestible and palatable, nutritious forage. Botanically, it belongs to the family Mimosaceae; it is the best-known species of the Leucaena genus and has a variety of common names. There are, however, at least 14 other species recognized in the genus.
The various species of Leucaena are perennial, deep-rooted, large shrub/small tree legumes growing up to 20 m tall. They have compound leaves with many thin leaflets, white flowers and produce a lot of seeds in pods. The leaves are a very good source of protein and can be used in both cut-and-carry and open grazing production systems. Re-growth occurs very fast after cutting. It can be used as shade in plantation crops, as living supports for climbing crops, such as passion fruit, and also for soil conservation and, being a legume, aids the maintenance of soil fertility. The mature shrub can be cut for poles for fencing and wood fuel and as bee forage.
Leucaena may be planted as single plants, single hedgerows, or multiple hedgerows, in cut-and-carry plots, grazed plots, along boundaries, or even along contours for soil erosion control. Leucaena and its companion browse legumes, such as Calliandra, Sesbania, Gliricidia, Mulberry, and Tree Lucerne, are well suited to backyard forage programs, contour forage strips, agro-forestry systems such as alley cropping, oversowing on sites with self-mulching soils, intercropping with perennial tree crops, and for soil conservation on stock exclusion areas.
The most important in Western Kenya are Leucaena leucocephalla and Leucaena diversifolia
Altitude: Leucaena grows from sea level up to 1900 m but performs best up to 1000m above sea level.
Temperature: Leucaena is a tropical species requiring warm temperatures (25-30°C day temperatures) for optimum growth. Leucaena is not tolerant of even light frosts which cause the leaf to be shed.
Rainfall: Leucaena can be found performing well in a wide range of rainfall environments from 650 to 3,000 mm. However, yields are low in dry environments. Leucaena is very drought tolerant even during establishment.
Soil type: Leucaena grows on a wide variety of soil types but does best on deep, well drained clay soils; it does not do well in acidic soils.
Plough and harrow to make a fine seedbed.
Establishment from the Seed: Freshly harvested Leucaena often has a high degree of hard seed due to an impermeable waxycoat which must be broken before the seed will imbibe water and germinate. Scarification to break this dormancy usually involves treatment with hot water (soak in warm water for 48 hours, or in boiling water for 4 seconds, or nip the broad (round) end); thereafter the seed must be inoculated before planting with a suitable Rhizobium strain which can be the same type as for calliandra or gliricidia, to ensure effective nitrogen fixation. The inoculant is first mixed with soil and then with the soaked seeds. Alternatively, Leucaena can be inoculated at the seedling stage. The inoculant is mixed in water and poured on the young seedlings. Another way is to collect soil from beneath an existing Leucaena stand and mix it with the nursery soil. Lime pelleting will protect the Rhizobium bacteria in very acid soils. Nursery propagation: For nursery propagation, use plastic tubes filled with free-draining soil, sand, and manure in the ratio of 3:2:1. Sow two seeds per tube. Water regularly as required and control weeds by hand pulling. One week after the seedlings emerge, thin to one seedling per tube.
Leucaena can be planted by directly sowing the seed or through nursery propagation.
Planting by seed
Large areas are best planted by directly sowing the seed in the final growing site. Make furrows 3 to 10 m apart and sow the seed at a rate of 1 to 2 kg per hectare, planting the seeds 2 to 3 cm deep.
Nursery propagation Raise seedlings in the nursery as described above. Transplant them when they are eight weeks old. For a pure stand prepare holes spaced 1 m by 1 m and at least 30 cm deep. For alley cropping or grazing, allow a spacing of 75 cm between plants and 3 to 10 meters between rows. Remove plastic tubes and place the seedling in the holes. Cover with moist soil and firm around the seedling. In widely-spaced rows for grazing, grasses may be planted between Leucaena rows to increase the total fodder supply to animals. Leucaena may be planted as single plants, single hedgerows, or multiple hedgerows depending on its use. When transplanting bare-rooted seedlings, leaves should be carefully stripped from the seedling to reduce moisture stress. If bare-rooted seedlings are planted the same day that they are dug from the nursery, 90 percent survival is possible.
At the time of planting or transplanting, apply triple super phosphate fertilizer at the rate of 120 kg per hectare, or one tablespoon (5g) per hole, and mix with soil..
When a fodder stand is harvested frequently and the fodder removed, nutrients are extracted from the soil. These nutrients enter the digestive system of the animal and a large proportion is excreted through manure and urine. To ensure sustainable fodder production, the manure and urine must be returned to the soil where Leucaena is growing. If the farm is on a slope, zero-grazing units for dairy cows can be constructed in such a way that all slurry is collected in a pit from which it can flow by gravity to fodder plots situated lower down the slope. When Leucaena has nodulated, it can supply its own nitrogen requirement. Although symbiosis with mycorrhiza fungus helps to absorb phosphorus, this element is likely to be the first that becomes deficient in the soil when no manure or urine is returned. A fertilizer rate of 100 kg P per ha (10 g per m) will normally be sufficient.
It is deep rooting and relatively drought tolerant. Once established, it is extremely tolerant of regular defoliation by cutting, grazing, and slashing. Excess growth should be cut and dried.
Leucaena seedlings are very susceptible to weed competition, therefore make sure the plot is weed-free when the seedlings are small..
The psyllids or jumping lice are small aphid-like insects adapted to feeding on the young growing shoots of leucaena. Mild infestations cause distortion of leaves whilst heavy infestations result in loss of leaves and attack by secondary moulds which feed on the sticky exudate of psyllids. It can wipe out the entire crop, especially of the species L. leucocephala. To control it, plant species that are resistant to this pest such as L. diversifolia. Biological control using a beetle and a parasitic wasp is showing promise.
Damping-off is an important fungal disease affecting seedlings in the nursery. This is controlled by good nursery techniques (overwatering promotes the disease) and use of well-drained soil media. The use of fungicides such as Benlate or Captan are also an option.
Start harvesting at the beginning of the second wet season by cutting back to 50 cm above ground level. Cut twice during the wet season when re-growth is 50-60 cm, or once at the end and conserve as dry leaf meal.
It is estimated that 3 kg of fresh Leucaena has the same effect on milk production as 1 kg of diary meal.
Leucaena is a high-quality, very palatable supplementary forage. It is best cut and fed fresh or as dry leaf meal. Feeding excessive amounts can cause bloat and hair loss, therefore leucaena should not make up more than 30% of the total ration. It should be fed fresh and not wilted or dried. 500 plants, planted in a hedgerow, provide enough leaves to supplement the diet of one dairy cow. .
Leucaena is drought tolerant and is also tolerant of grazing and slashing. First grazing may be done when the plants are 1.5 m in height but it should be light at first. Avoid heavy grazing until the plants are fully mature, from 1 to 3 years old. Grazing or harvesting intervals can be 6 to 8 weeks or 12 weeks in less favorable conditions..
Leucaena, just like the other fodder trees provides high-quality low-cost fodder all year round. Because most of them are leguminous plants, their leaves are rich in protein and an ideal feed to supplement grasses and crop residues. Often animals get used to them only slowly, but once they acquired a taste for them and accept them, tree forages have a highly beneficial effect on milk and meat production.
Nutritive value: L. leucocephala foliage is noted for its very high nutritive value for dairy cattle production. Typical values for the edible fraction are 55-70% digestibility, 3-4.5% N, 6% ether extract, 6-10% ash, 30-50% N-free extract, 0.8-1.9% Ca and 0.23-0.27% P. Na levels are generally below requirements for ruminants at 0.01-0.05%. Leaves also contain 2-6% condensed tannins (CT), phenolic compounds which bind and protect the dietary protein from degradation in the rumen. Providing that the protein-CT complexes dissociate post-ruminally allowing N absorption in the lower gut, CTs have the potential to increase protein uptake.
Toxicity: Contains mimosine, a non-protein amino acid that has antimitotic and depilatory effects on animals. Concentrations in the young leaf can be as high as 12% and the edible fraction commonly contains 4-6% mimosine. Mimosine is acutely toxic to animals but is normally converted to 3-hydroxy-4(IH)-pyridone (DHP) upon ingestion. DHP is goitrogenic and, if not degraded, can result in low serum thyroxine levels, ulceration of the esophagus and reticulo-rumen, excessive salivation, poor appetite and low live-weight gains, especially when the diet contains more than 30% Leucaena.
Leaf yield is maximized by cutting at 6-12 week intervals during the growing season. Yields in extensive hedgerow plantings in the dry tropics and subtropics generally range from 2-6 t/ha/year. Very high yields (>15 t/ha/year) in southeast Asia and Hawaii, with plants 0.5-1.0 m apart in rows 1-3 m apart. Fuelwood yields compare favourably with the best tropical trees, with height increments of 3-5 m/year and wood increments of 20-60 m3/ha/year for arboreal varieties.