Leucaena leucocephala (Lamk) de Wit - flowering and fruiting branch
Leucaena has the highest quality feed of any tropical legume, and the potential to produce the highest high weight gains. Steers can gain 300 kg of live weight in a year with adequate leucaena, and irrigated leuceana has produced over 1000 kg of LWG per ha per year.
Leucaena is best suited to deep well-drained fertile soils of neutral to high pH; its deep root allows it to produce new leaf after shallow-rooted grasses have run out of moisture. Its leaf is killed by frost, but its height protects it from ground frosts and it shoots again with the onset of warm conditions.
Since 1980s, leucaena has been attacked by the psyllid insect (Heteropsylla cubense) especially in hot humid conditions. As a result, the main regions for leucaena are now in drier inland Queensland, often on fertile brigalow soils where some tens of thousands of hectares have been sown.
Hard seed must be treated with hot water (80oC for 4 minutes or boiling water for 4 seconds); seed must be inoculated with specific rhizobium, and can be pelletted with lime for more acid soils.
In the dry regions, leucaena is planted as a crop 2-4 cm deep in a fully cultivated seed-bed in rows 5-9 metres apart. The rows are kept weed-free with herbicideand the inter-row area is kept weed-frer through cultivation for the first year as the legume seedlings are very susceptible to competition. Nitrogen-loving grasses (green panic, Bambatsi panic and Callide rhodes) can be sown in the second year.
Leucaena is usually rotationally grazed because it is so palatable, or grazing is deferred over summer to provide high quality feed in autumn. The young leaflets of leucaena contain an alkaloid, mimosine. With abundant leucaena in the diet, excessive mimosine causes loss of weight and hair. CSIRO researchers isolated a rumen microbe that can break down mimosine, or its product (DHP), and this should be introduced to stock eating vigorous stands of the legume.
The main cultivars have been Peru and Cunningham (multi-branched types) , with Cunnigham being slightly more vigorous, but a new cultivar Tarramba (a more tree-type) is more productive and will grow under cooler conditions.
Plant breeders are crossing Leucaena leucocephala x L. diversifoia to develop psyllid-resistant and more cold-tolerant varieties. However, their feed quality is lower than that of leucocephala, and weight gain of steers may be better on leucaena affected by psyllids than on the hybrids.Die back of leucaena from a root fungus has been experienced in the Ord; die-back has also occurred in central Queensland but the cause of this is not yet known.
Naturalised leucaena is considered an environmental weed where it has formed thickets.
Planted leucaena should be managed to reduce flowering and seeding. Patches of dense seedlings should be grazed or slashed. The Queensland Leucaena Growers Network has developed a Code of Practice for good management.
|Creator: Ian Partridge,
Date created: 14 April 1998 Revised: 15 January 2003