Leucaena trees will fully repay your efforts to obtain uniform germination and good establishment. Like other trees, leucaena establishes slowly, and “tender loving care” is advisable.
- Seed Source/Provenances. NFTA has a tremendous number of varieties of leucaenas available, and specific ones are recommended for different uses and environments. These recommendations are continually being revised as new varieties and hybrids are developed. Based on present availability, we recommend KX3 (hybrid), K636 (L. leucocephala), K156 (L. diversifolia), K217 (Salvador), and K29 (Honduras) for tree types. These are some of the most psyllid-resistant varieties presently available. An excellent forage variety is Australia’s “Cunningham”, but tree types also are outstanding in forage yield when properly managed. KX3 and K156 do well in cooler elevations or latitudes. Exciting new varieties are being identified for psyllid-resistance, but seed won’t be available until late-88 or 1989.
- Seeds. Good seeds should be well dried, insect-free, fungus-free, and weed-free. “Giant” varieties have about 20,000 seeds per kg, common varieties about 30,000. Seed sources are listed annually in Leucaena Research Reports, or can be obtained from this address.
- Storing Seeds. Keep seeds dry in a tightly-closed plastic bag or jar, and they will last for years, longer if refrigerated.
- Scarification. Seeds do not germinate well unless they are scarified by scratching or cracking the tough, water-impervious seed coat. of the following 2 ways, the first is worth the time when small numbers of seeds are being planted. The second is most commonly practiced for large batches:
- Scratch or nick the round end of each seed with a knife, small scissors or file. Works 100%.
- Hot water treatment; vigorously boiling water is poured over seeds, about two liters per kilogram of seeds, stirred gently and poured off in 3 minutes. Alternatively, 80 C for 3 minutes. About 75% germination.
- Inoculation. Leucaena is a legume, and bacterial inoculation is necessary for good modulation and growth. Use of soil from areas where leucaena is already growing often suffices. Most tropical soils contain appropriate bacteria, but preliminary tests are advised. Inoculum can be obtained from NifTAL, P.O. Box “O”, Paia, Maui, Hawaii 96779.
- Transplant or Seed Directly? Leucaena establishment is slow, with at least 6 weeks in a small seedling stage (to 30 cm). At this stage, the seedlings are extremely susceptible to weed competition. Transplanting of nursery-grown stock will typically give higher survival rates than direct seeding because the seedlings have a head start in terms of competition. However, raising seedlings requires extra labour in the nursery and in transplanting. Good weeding is necessary if leucaena is direct seeded. After the small seedling stage, growth is more rapid, and trees can effectively compete with weeds. For a small local nursery, almost any type of seedling container can be used. However, the roots of seedlings raised more than 6-8 weeks in containers spiral and become rootbound, leading to poor root growth in the field. For this reason, seedlings should not be kept too long in the nursery, or open-ended containers should be used, and given regular root-pruning. A rich soil mixture is recommended for the nursery. Peat or other organic matter should be added to enrich poor soils. Fungi causing damping off are not serious on leucaena, but use of a fungicide may be advisable for large-scale production. Bare-root transplanting and stump cuttings can work. For stump cuttings, cut the root at 15 cm, the shoot at 25 cm, and keep moist until they are planted.
- Planting. We recommend spacings ranging from 1×1 m to 2×2 m for woodlots; rows 1 m apart with trees 10-20 cm apart within the rows for fodder banks (forage grasses can be intercropped between the rows); and for alley cropping, planting in rows (on contours) that are 2-3 m apart. The spacing within the rows for alley cropping depends on the slope of the land. For flat to moderate slopes, 20-50 cm between trees will give maximum tree and crop production. For steeper slopes, closer spacings are recommended for better erosion control. initial spacings as close as 2.5 cm between trees have been used successfully on very steep slopes in the Philippines. These trees should be thinned to wider spacings as they mature. Good initial land preparation and weed control are extremely important.
- Environment and Soil. Leucaena thrives in semi-arid to wet tropics, with best performance when moisture is not limiting. It prefers warm climates and neutral soils, though cold- and acid soil-tolerant varieties have been developed. It does not tolerate frost, though frost-burned plants will regrow. Different provenances perform better in different conditions, and provenance trials are advised.
- Pests and Diseases. Insect or disease controls have not been advised for leucaena. The psyllid insect (Heteropsylla cubana) can cause economic damage in the absence of predators, and use of resistant varieties is recommended. Young seedlings require protection from browsing animals. Root rot occurs in poorly drained sites.
- Harvesting Seeds. Leucaena varieties are generally highly self- fertile. Choose outstanding, uniform trees and rogue out plants that are off-type, slow-growing, or producing seeds too prematurely or frequently. Harvest and dry the seeds, label carefully as to variety and source, and store as noted above.
For additional information, write:
James L. Brewbaker (author), President, NFTA, P.O. Box 680, Waimanalo, HI 96795. (Varieties, species, fuelwood production).
Ray Jones, Davies Lab., CSIRO, Townsville, Queensland 4810, Australia. (Forage production, nutrition).
A publication of the Forest, Farm, and Community Tree Network (FACT Net)