Tree information

Local name: 

ipil ipil (इपिल इपिल)

Genus: 

Leucaena

Species: 

leucocephala

Author: 

(Lam.) de Wit

Family: 

Mimosaceae

Leucaena leucocephala is native to Central America, from Mexico to Honduras, and also occurs in Peru. A low, shrubby type of Mexican origin was introduced to south Asia probably at least a century ago, and has been collected in Nepal. Much more recently giant arboreal types, which can grow into large trees, have been introduced from Salvador and Guatemala. Trees of different origin vary considerably in their growth, silvicultural requirements, and tolerance or resistance to psyllid attack; hence variety is most important.

Characteristics

The giant arboreal types of Leucaena are trees capable of growing to 20 min height. They are normally evergreen, but will shed their leaves during periods of prolonged drought or frost. They will tolerate partial shade, but grow best in full sun. Most cultivars tried grow best below 1000 m; at higher altitudes they may survive, but growth is likely to be poor.

Leucaena is sensitive to soil pH and where this is less than five growth is seriously reduced (Ahmad and Ng, 1979). It is also sensitive to relatively small differences in soil fertility, and within the same plantation very vigorous trees may be found growing within a few metres of poor stunted ones. In the constantly humid tropics, such as in the Philippines, it has been used successfully for reafforestation of denuded slopes, but in areas with a pronounced dry season it requires soils of at least moderate fertility. In Nepal it generally grows well on Bhabar Terai soils, but has failed on very gravelly and bouldery soils near rivers, though these soils are capable of growing good crops of Dalbergia sissoo and Acacia catechu. More needs to be learned about the tolerance of different Leucaena cultivars to different soils and altitudes in Nepal.

In the constantly humid tropics, such as in the Philippines, Leucaena will competc with and eventually dominate lmperata grass, but this is not the case in drier areas such as Ncpal, where thorough weeding is necessary if successful plantations are to be established. Young seedlings are killed by frost, and the trce should not be planted in frosty areas. They are very palatable to grazing animals including deer, and it is not practicable to plant Leucaena in areas where wild game is abundant, as the cost of erecting deer proof fences is prohibitive. Trees are fairly resistant to fire, but repeated fires will kill them.

Flowers and seed are often produced at a very early age, often less than a year. According to Hawkins (1986), at Adabhar in the Bhabar Terai varieties which flowered early also suffered from up to 1m shoot dieback during the dry season, while those which did not flower before 18 months avoided this.

The seedlings and older trees have very strong taproots. Rhizobial nodules which fix nitrogen are found on the roots, and if the appropriate strain of the Rhizobium bacterium is absent growth is considerably reduced. In some parts of Nepal inoculation by Rhizobium may occur naturally from bacteria within the soil, but this cannot be relied on and artificial inoculation in the nursery is a neeessary safeguard. Leucaena coppices very readily. Even if stems little over 1 cm in diameter are cut, the roots will frequently send out new shoot.

Artificial regeneration

The potting mixture used for raising seedlings should not be more than slightly acid; preferably the pH should be six or more. The seed should be sown directly into polythene bags, and any surplus seedlings pricked out into empty pots soon after germination is complete. For raising plantable stock 8-10 weeks in the nursery will be needed in the Terai, and 10-12 weeks in the inner Terai. Above 1000 m Leucaena will rarely be raised in nurseries. No shade is needed. The seedlings rapidly develops a strong taproot, and frequent and regular root pruning, every 10-14 days, is essential. If the taproot has once been allowed to develop, drastic root pruning is likely to kill the seedlings, even if the shoot is reduced at the same time (J. Stewart, 1983).

In some nurseries seedling growth has been very slow. Some of these were at high altitudes, where slow growth is to be expected, but slow growth was also recorded at some low-altitude nurseries, despite hot water treatment of the seeds. It is possible that this was due to lack of inoculum, to an unsatisfactory potting mixture, or to an unsuitable variety. Leucaena can also be established by using stumps.

With the arrival of the psyllid the most important aspect of different varieties is their resistance to or tolerance of psyllid attack. Unfortunately some of the varieties which up to the present have produced the highest yields (K 8, K 28, K 67) are very susceptible to psyllid. At Adabhar the hybrid L. leucocephala x L. diversifolia, K 743, had at the age of 42 months a cumulative yield from thinnings (half the crop pollarded at 19 months, the other half at 42 months) of 10 t ha-1 yr-1 oven-dry wood biomass, but became heavily infested by the psyllid, as was the Sunsari land race included in the same trial (Neil, 1990). A hybrid of these two species, provenance unstated, also did very well at Lampatan, near Pokhara (900 m); it provided the highest yields of fodder from lopping of all the Leucaena provenances included in this trial. but this was before the psyllid reached the area (Veldhuis,  1988).

K 636 had the best height growth in a trial at Adabhar (6.0 m in 22 months) and up to 1989 had suffered no damage from psyllid in Nepal, according to L. Joshi, although it is susceptible in other countries. It tends to be a rather tall, slender tree with less volume production in relation to height than some other varieties; for instance at Sagarnath at 3.5 years old it had the second best height growth (6.2 m), but only 55 per cent of the volume growth of thy best variety. K 156, L. diversifolia, was second best in height growth at Adabhar (5.9 m in 22 months), but again is of relatively low volwne production. At Sagamath the mean weight of wood per tree was slightly less than 50 per cent of that from the best variety. a local land race from Tarahara. It has been found to be fairly resistant to psyllid in Taiwan and elsewhere.

Among highly resistant species and varieties according to L. Joshi are L. collinsii, K 740, and L. esculenta, K 897; also L. pallida, K 376, and L. retusa, though growth of the last was poor. The hybrid KX 3 planted at 1300 m had only one adult psyllid. Other resistant hybrids, KX 1 (L. pallida L. diversifolia), and KX 2 (L. pallida x L. leucocephala) are promising. In addition to K 156, the variety K 145 of L. diversifolia is also promising. Most of these varieties are under trial in the World Neighbours' project at Bahunipati at about 1000 m. Another aspect needing investigation is to find varieties capable of growing above 1000 m, where in general L. leucocephala does badly.

Of these by far the most important is the psyllid Heteropsylla cubana, sometimes known as the jumping plant louse. L. Joshi (1990) has given an account of its arrival in Nepal. This pest reached Hawaii in 1984, and from there has spread south and west, reaching Nepal probably around April 1989. By July 1989 there was heavy infestation between Dharan and Dhankuta 10 eastern Nepal, and by August a few insects were found in Hetauda and Pokhara. As the insect is spreading from east to west it is likely that most parts of Nepal will be affected eventually.

As has been previously pointed out plantations need thorough weeding until the trees have become established. For fuel and fodder plantations, planting at a close distance, such as 1 m x 1 m, could be tried. Depending on the growth of the trees, during the second year after planting alternate trees or rows of trees could be coppiced or pollarded for fodder and small fuelwood, and the shoots from the cut stems from then on be cut regularly for fodder, leaving the remaining trees to grow on for fuelwood production. Young plantations need careful protection against browsing, as has been noted earlier.

Although Leucaena plantations have been successfully established by direct sowing in many parts of the world there are problems in using this technique. The main one is that early growth of the seedlings from seed sown directly in plantations is slow. It may take a year in the plantation to obtain the same height growth as is reached in two months in the nursery; meanwhile the seedlings need very thorough weeding. Unless Leucaena is raised in conjunction with agricultural crops the use of seedlings raised in polythene pots is more reliable.

Rates of growth from past trials are of little relevance at present until the effect of the psyllid on growth is clearer. Although in the constantly humid tropics very high growth rates, with mean annual increments of 30-40 m3 ha-1, have been recorded these are unlikely to be reached in Nepal, where 20 m3 ha-1 would be a more likely figure, provided the psyllid problem is solved.

As noted above many varieties of Leucaena seed prolifically from a very early age. They often produce seed almost all the year round, but November to January have been recorded as the months for seed collection in Nepal. There are 20,000 to 26,000 seeds kg-1. The seed can be stored for many years without losing its viability; indeed seed stored in Paris at room temperatures still gave some germination after 99 years (Barton, 1961). It should be dried and stored in sealed containers, and a little contact insecticide should be mixed with it, as it is very liable to borer attack during storage.

The seed has a hard impervious coat and needs treatment before it is sown, otherwise germination may take many months. Small quantities of seed may be manually scarified by cutting off a small portion of the coat at the opposite end to the hilum; Napier (1987) found this the most effective method, giving more than 80 per cent germination within eight days.

For larger quantities this is very laborious, and hot water treatment may be used instead. Water is brought to the boil, removed from the heat, and the seed kept in it for 2-3 minutes before being soaked in cold water for 24 hours. Alternatively it may be soaked in water at 80°C for two minutes, and then put in cold water as before. Napier found that treatment with hot water for five minutes caused about 12 per cent of the seedlings to imbibe water. These imbibed seeds had lower germination; combined germination of imbibed and non-imbibed seeds was 78 per cent after 20 days. Keeping the seed in boiling water for five minutes reduced germination.

The standard method of inoculation of Leucaena seed is by the use of Rhizobium culture, which it may be possible to obtain from the Department of Agriculture, Khumaltar. Different strains of Rhizobium are available for neutral or alkaline soils, and for acidic soils. The Rhizobium culture is mixed with an adhesive such as two per cent gum arabic solution, and the seeds are coated with this mixture. This treatment should be applied after the seeds have been treated with hot water. After coating with inoculum the seeds are dried, and they should then be sown within week. If it is impossible to obtain Rhizobium inoculum, soil should be collected from beneath vigorous Leucaena trees and mixed with the potting mixture. This method was used successfully in Hetauda nursery, using soil from well-grown Leucaena at Nijgad. The soil used for inoculation should if possible come from trees growing on a similar soil type to that on which the Leucaena will eventually be planted.

Importance in Nepal

The potential value of Leucaena in Nepal cannot be evaluated until the effects of the psyllid are clearer. If, as has happened in some countries, one or two years after the first arrival of the psyllid the severity of the attack diminishes, it is possible that in Nepal the eventual level of infestation could be tolerated. There are also the possibilities of finding resistant varieties, and biological control.

At Bahunipati, Sindhupalchok District, at between 900 and 1000 m, the World Neighbours organization had been very successful in persuading farmers to grow Leucaena along their terrace risers. The trees were planted in June at 1 m spacing, in pits with compost, and in six months had grown.beyond the reach of the livestock that were allowed into the fields at that time to graze the stubble; during the next monsoon and thereafter lopping for fodder was possible; every 2-4 weeks. Contour hedges from direct sown Leucaena were also established in farmers' fields. The use of Leucaena had been widely accepted by local farmers, who up to 1988 had planted nearly 59,000 trees. The main variety used was K 8 (Arens, 1984; Baidya, 1990). Unfortunately the area has become severely affected by psyllid, and the whole scheme is having to be re-thought.

Leucaena is a multipurpose tree. producing fodder, fuelwood and small timber. and improving the soil. The fodder is highly nutritive and is comparable to lucerne. Its content of crude protein ranges from 15 to 21 per cent, with a digestibility factor of 50 to 70 per cent, and between 55 and 70 per cent digestible nutrients. The main disadvantage of Leucaena as a fodder is that it contains mimosine which is toxic, especially to non-ruminant animals such as horses, pigs and poultry; for this type of animal Leucaena leaves should not form more than five per cent of their diet. Ruminants (cattle, sheep, buffaloes), are different in that they can degrade mimosine to another substance, DHP (3-hydroxy-4 (1 H) pyridone), in their digestive system.. Unfortunately DHP tends to cause goitre and other disturbances. However, in some parts of the world ruminants have bacteria in their digestive systems which can degrade DHP and remove this danger, and such animals can thrive on diets containing a high proportion of Leucaena leaves. It has been found that if a few animals which have these bacteria are introduced among others which do not have them, the whole herd very rapidly obtains the bacteria and symptoms of Leucaena toxicity disappear. This is a simpler method of overcoming the problem of Leucaena toxicity in ruminants (R. J. Jones and Bray 1983; Lowry, 1983). Dry matter yields of fodder can be as high as 20 t ha-1 yr-1, but in the dry tropics 8 t ha-1 yr-1 would be a good yield.

Leucaena produces a good fuelwood, with a weight of about 540 kg m-3 and a calorific value of 17,600 to 19,300 kJ kg-1. It also makes a good charcoal. The wood can be used for poles, and has potential for sawn timber and paper pulp.

The tree fixes large quantities of nitrogen and hence is a soil improver. It has been used as a shade and nurse tree for coffee and tea, and has been. suggested for use as a green firebreak. It has also been used in alley cropping, where hedges of Leucaena are planted between agricultural crops, and the loppings from the hedges used as a green manure.

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