Leucaena is a legume fodder crop that grows in tropical and subtropical environments.
Leucaena provides high quality feed for ruminant animals that boosts liveweight gain both per animal and per hectare, compared to grass-only pastures.
Leucaena performs best in tropical climates (hot, wet summers and mild winters) and effectively stops growing when the average day temperature falls below 15oC.
Preferably, annual average rainfall needs to be above 600 mm.
Leucaena is frost sensitive, however will re-grow from stored soil moisture in spring.
Leucaena will grow in a wide range of soils but is most productive in fertile (high phosphorus and alkaline pH), deep (>1 m), well-drained soils (intolerant to waterlogging).
Being a tropical plant, leucaena is susceptible to frost and is therefore more productive in frost-free areas. Light frost will cause leaf fall while heavy frost can kill all above-ground plant material, requiring regrowth from the crown.
Align row direction for ease of mustering. Also consider erosion risk during paddock preparation and establishment. Where possible, provide water in laneways.
Continual intensive grazing will severely stunt and/or kill leucaena, so protection of young plants is essential. Plant sufficiently large areas or fence small areas from hares, wallabies, kangaroos, emus, etc.
Control woody regrowth prior to establishment of leucaena.
Protect the long-term future of leucaena as a pasture plant by stopping it becoming a weed around your farm or neighbouring properties. Do not plant leucaena close to waterways or boundaries to minimise the weed potential (follow the guidelines in The Leucaena Network's code of practice).
Seedbed preparation, stored soil moisture and weed control are the keys to successful leucaena establishment.
When cultivating, prepare the paddock as for any crop - cultivate to control weeds and prepare a seedbed, or use herbicides to control weeds.
If preparing strips in an existing grass pasture, strips need to be at least 4-5 m wide.
Fallow to store a minimum of 60cm of soil moisture. More is better. This may take 6-12 months depending on rainfall.
In weedy paddocks, ensure sufficient preparation time to reduce the weed seed bank and use a residual herbicide once sown.
Planting and establishment
Plant when soil temperatures are above 18°C, and with at least 60 cm of soil moisture.
Follow-up rainfall will greatly assist establishment. Avoid planting times when there is a high risk of hot, dry conditions during establishment (e.g. during spring).
Planting rate and depth
Aim to sow 2 kg/ha of high germination 'soft' seed. Seed should be spaced about 5 cm apart in the row.
Ensure the seed is mechanically scarified and inoculated with correct rhizobium (Leucaena/desmanthus strain).
Plant the seed into wet soil sufficiently deep to stay wet for a week, but no deeper than 5 cm. Run press wheels to the side of the seed, not over the top.
Row spacing and plant population
Row spacings from 5-12 m are used commercially..
If rows are too narrow, grass persistence will be poor (shading) and grass production low (competition).
If rows are too wide, vigorous grasses compete for soil moisture and nitrogen benefits are diluted. This will result in insufficient leucaena at high grazing demand periods.
Aim to establish 5-10 plants per metre of row.
Four commercial cultivars are available, all of which are susceptible to psyllid attack:
- Peru is shrubby with good basal branching.
- Cunningham generally produces more dry matter and edible material than Peru and is a prolific seeder.
- Tarramba is taller, more tree-like, produces less seed and has greater early seeding and cold vigour. It is susceptible to psyllid attack but grows sooner after psyllid damage.
- Wondergraze is the latest release which has similar early seedling vigour and psyllid tolerance but is bushier than Tarramba.
A new psyllid resistant variety is soon to be released. It will be highly suited to coastal districts where psyllids can significantly reduce forage production.
Weed and insect control
Weed control in the establishment phase is critical for success - leucaena is a very poor competitor when young.
Use a residual herbicide (e.g. Spinnaker®) at planting over the rows to control broadleaf and grass weeds.
Alternatively, inter-row cultivate to control weeds, particularly if legume weeds (e.g. sesbania) are a problem.
It is essential to control soil insects during establishment.
For optimal production, cattle need to have access to plenty of grass for roughage and energy. Leucaena provides highly digestible protein.
Leucaena performs best in fertile soils with:
- phosphorus above 20 mg/kg
- sulfur above 5 mg/kg
- good levels of calcium and trace elements, particularly zinc and potassium.
No nitrogen fertiliser will be required if the plant has adequate soil nutrients and is effectively inoculated.
For optimal production, cattle need to have access to plenty of grass for roughage and energy.
Leucaena contains a toxin called mimosine that can cause weight and hair loss. Upon introduction, cattle need to be inoculated with the 'leucaena bug', a rumen bacteria which can be sourced from the department's Tick Fever Centre at Wacol (Brisbane). To maintain the bug in the herd, retain a couple of head from the initial herd to introduce into the next mob.
Leucaena is tolerant of periodic heavy grazing; however, resting is critical for long-term productivity.
Healthy leucaena/grass pastures are highly suited to rotational grazing systems. Continuously grazing leucaena does not maximise productivity and may lead to height control issues.
Leucaena is a tree and, under light grazing pressure, will grow beyond the reach of cattle. Ensure periodic intense grazing pressure to pull down the tall runners and keep leucaena as a leafy branched shrub. This minimises the need for chopping and reduces flower production and seed set.
Follow the guidelines in The Leucaena Network's code of practice, as plants that produce seed can contribute to the weed spread of leucaena.
Leucaena and the environment
Good management of nitrogen-producing leucaena enables a productive and vigorous grass that provides high ground cover year-round, maximising water capture and reducing run-off and erosion.
Effectively nodulated leucaena will produce sufficient nitrogen for its own needs. However, incorporating a vigorous companion grass maximises pasture production and improves soil fertility and organic matter production. This will improve soil health and structure.
Leucaena is a deep-rooted perennial plant that has a high water requirement (roots have been found to a depth of 5 m). This high water use can create massive cracking in some soils, assisting infiltration during heavy storms.
Deep roots enable leucaena to remain productive and provide quality feed during periods of dry weather when shallow-rooted grasses have stopped growing.
Manage leucaena so cattle have access to all available feed.
Weed potential and the code of practice
Leucaena is a highly productive plant but can constitute a weed if seeds spread and germinate away from grazing animals.
Leucaena can produce large amounts of dormant seeds that will germinate over a number of years.
Unwanted plants can be easily controlled using a woody weed herbicide such as Access®.
The Leucaena Network has developed a code of practice that all producers should follow to maximise the productivity of leucaena while minimising the weed potential.