CLIMATIC REQUIREMENTS

Taxonomic name: Leucaena leucocephala (Lam.) De wit

Synonyms: Acacia leucocephala (Lamark) Link 1822, Leucaena glabrata Rose 1897, Leucaena glauca (L.) Benth. 1842, Mimosa leucocephala Lamark 1783.

Common names: Subabul (India).

Description The genus Leucaena is distinguished from all other Mimosoid legumes by its hairy anthers which are easily visible with a hand lens. Leucaena leucocephala is distinguished from other species of Leucaena by its intermediate leaflets and large pods in clusters of 5-20 per flower head. It forms a small to medium-sized thornless tree 3-15 (20) m tall and 5-50cm bole diameter. The leaves are bipinnate with an elliptic convex extrafloral nectary on the petiole, 4-9 pairs of pinnae and 13-21 pairs of leaflets per pinna. The leaflets are 9-16mm long and 2-4.5mm wide, nearly sessile and strongly asymmetric linear oblong and acute at the apex. The flowers occur in 12-21mm diameter heads, are cream-white, with ten free stamens per flower and hairy anthers. The pods occur in crowded clusters of 5-20 per flower head and are 11-19cm long and 15-21mm wide pendulous, flattened and papery, and passively dehiscent with 8-18 seeds per pod. Three subspecies are recognised, two of which - subsp. leucocephala and subsp. glabrata have been introduced pantropically.

Soil:

The species grows well in loamy soils, clayey loam and sandy loam. It has a long strong tap root and can penetrate deep in compacted soils. The species has foliage which fertilizes the soil, as the fallen leaves decompose fast and form good humus to add soil nutrients. The species is an excellent nitrogen fixer thereby helps to augment the soil fertility. 

Temperature:

The species tolerates high temperature of the tropics. Heavy frost kills the plant, light only defoliates the tree. It is a light demander and grows slowly under the shade, though tolerates partial shade.

Rain fall:

The species grows best where the rainfall is between 1000 to 3000 mm. It however tolerates dry season extending 8 to 10 months, but the productivity is reduced.

Utilization:

All parts of the tree are useful. Foliage is a good fodder for cattle, though due to mimosine, which form 3-5% of the dry matter, there is a fear of its ill effects on the health of the cattle. However upto 10 to 15% of the diet of cattle can be lucaena fodder without ill effects. Even curry is made of this leaf. The seeds are safe as a coffee beverage. The pods can be spread on roofs to insulate from heat. The wood is good for small furniture, as poles and for plywood core etc. Unripe pods are also eaten by goats and cattle. It is a good fuel with heating value of 4640 k/cal per kg, when harvested from plantations of 2 to 5 years age and the heating value increases with maturity of trees. As pulpwood, subabul is among the best tropical hard woods. The pulp is high in holocellulose and low in silica, ash, lignin, alcohol benzene solubles and hot water solubles. All these are important for pulp and rayon. The pulp yield is as high as 50 to 52%. The fibre is shorter than in softwoods, but is within the acceptable range. It has however low tearing strength, low folding endurance and average tensile strength, compared to others softwood pulps. Subabul is a good crop for greening the degraded and denuded lands, as it improves the soil condition. It is a good plant for shelter belts and wind breaks for horticulture crops. It is a good fibre break as well.

PLANTATION TECHNIQUES AND PRACTICES

SEEDS: Seeds come out of pods which grow in clusters, from mostly self pollinated flowers, which look like fluffy white ball. The seed has a waxy white coat, and needs to be treated. In a KG, giant types have about 20,000 seeds. In general there are 30,000 seeds in a Kg of 100% purity with about 6% moisture. SEED COLLECTION: Ripe pods should be collected before they split and dried in the sun for 3 to 4 days. The pods then split, when seeds can be gathered by sieving. Seeds are viable for three to four years.

PRETREATMENT:

As the seed coat is hard, they need pretreatment before sowing: This can be done with any of the following ways.

• Soaking the seed in hot water (800) for Two to Three minutes, or in cold water for 3 to 4 days.

• Concentrated Sulphuric acid can also be applied for 15 minutes to soften the seed. Germination occurs in seven days with 70 to 80% germinating.

Planting:

Direct sowing of seed during monsoons gives good result, but the plants grow slower than nursery raised seedlings and if there is prolonged drought the germinated seed may dry up.

NURSERY TECHNIQUES

BAG CULTURE:

Pretreated seed should be sown in poly gags of 5" x 8 " (12.5 x 20 Cms), filled with soil mixture to which Rhizobium inoculum (Soil from older plantations) is added at 250 gms for 20 Kgs of seed.

Pretreated seed can be sown in nursery beds of 40' x 4' thinly covered with soil (soil cover should be 3/4th the thickness of seed). Seedlings when 10cms tall, can be pricked out and planted in poly bags filled with soil mixture.

STUMP PLANTING:

As the species is a good coppicer, recent trails with stump planting has given good success. Good pretreated seed be sown on nursery beds.

Beds should be formed with red earth, sand, farmyard manure and local soil, to which soil from the older plantation is added. When the seedlings are 3 to 4 months old, and when the collar thickness is that of an index finer, they be taken out of the beds and stumps formed by cutting the shoots and roots. The stump should be of the thickness between thumb and index finer. The length should be between 9" to 12" (22.3 to 30 cms.). The hair roots and the long thin tail of the tap root should be cut with a sharp tool. The stump should have only about 20 Cms of the shoot.

This stump can be transported in wet Hessian bags. Before bagging, the stumps be made into bundles of 50-100, and dipped in a puddle of red loamy soil to which a little quantity of Gum is added. This soil coat will prevent dryage of the stumps during transport and storage. They should be planted within 3 days of formation.

Stump planting has advantages in costs and handling and transport. As planting can be done in crow bar holes, costs on digging of pits for bags can be saved. Once the stump establishes and puts on growth, the plantation will be as good as that raised with bag plants.

SPACING

Spacing can be varied to suit the end use. For purposes of fodder, the spacing can be 50 x 50 cm. For fuel wood the spacing can be 1m x 1m; for Pulpwood, as the minimum girth is 10 cms, and if harvesting is done in the fourth year, the best spacing will be 3 m x 1.5 m. Farmers are planting in general at 50" x 50" spacing.

In general, the spacing should be closer in poorer soils and wider in fertile rich soils.

Season of Planting:

Planting should be done during rains when the moisture is available at depths of 12". Bagged seedlings be planted in 30 cms cube pits.

Stumps should be planted in crow bar holes. The planted stump should be firmed up on all sides. Care should be taken to see that no hollow is allowed to remain in the crow bar hole.

After Care:

Weeds are a major cause of failure or slow establishment. Regular weeding, till plants are one to two meters tall, gives best results. Weeding with soil working round the plants to a radius of 0.5 m should be done at least thrice in the first year, and as many times as needed in the subsequent years.

If the planting is done at 3 x 1.5 m spacing, the space in between rows, can be ploughed with a tractor. Such operation gives very good result. Irrigation if possible accelerates the growth. Singling of multiple shoots, by retaining one or two at each plant, will give good girth increment of the retained shoot. If pruning is to be done to collect green manure or cattle fodder, it should be limited to 2/3rd the bole, leaving intact the 1/3rd crown.