NFTA 93-03, June 1993
A quick guide to useful nitrogen fixing trees from around the world
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NFT Highlights
NFTA 93-03, June 1993 A quick guide to useful nitrogen fixing trees from around the world |
Chamaecytisus palmensis: hardy, productive fodder shrub
Chamaecytisus palmensis is a fast-growing shrub or small tree
adapted to temperate regions with winter rains and prolonged, dry summers.
In addition to producing high yields of palatable, nutritious fodder, the
shrubs provide welcome shelter for livestock, help control soil erosion
and salinization, increase soil fertility through nitrogen fixation, and
produce nectar for bees. If allowed to develop, thick branches provide
fuelwood that burns with intense heat.
Called "tagasaste" on the island of La Palma in the Canaries,
where it originates, the species was formerly known as Cytisus proliferus.
After its introduction to Australia, it was given the misleading common
name of "tree lucerne" (Webb, 1982).
Botany
Chamaecytisus palmensis is a member of the Papilionoideae
subfamily of legumes. If managed as a single-stemmed tree, it reaches heights
of 7 to 8 m, but its common growth form is a multi-stemmed, spreading shrub
of 5 to 7 m. The branches droop, the leaves are on short petioles, and
the single lanceolate leaflets are pubescent below. Seed pods are 4 to
5 cm long. They become black on ripening, and contain 8 to 12 black seeds.
About 35,000 to 40,000 seeds weigh 1 kg.
The shrubs have no thorns and produce profuse masses of fragrant
white pea-like flowers in early spring, making them attractive ornamental
plants. The white flowers distinguish C. palmensis from related,
unpalatable species that have yellow flowers.
Ecology
To date, successful growth has been restricted to temperate regions
with wet winters and dry summers, with annual rainfall ranging from 350
to 1600 mm (Douglas, 1987). The shrubs tolerate
a wide range of temperatures: They grow vigorously to the southern
tip of New Zealand (46°S) and are naturalized in Australia as far north
as Toowoomba (27°S). They are found from sea level to elevations of
1000 m and are reported to survive at 3000 m in Ethiopia (ILCA, 1987).
Cultivars develop that are suited for specific environments.
In Australia, seedlings proliferate vigorously along roadsides near Orange,
New South Wales, despite annual frosts down to -15°C.
Seedlings survive with equal vigor in deep coastal sands in the hot
and arid climate of Geraldton, Western Australia.
Chamaecytisus palmensis establishes most easily on sandy-surfaced
soils, but tolerates a wide range of soil types including gravels, loams,
acid laterites and limestones. The shrubs tolerate a pH range of 5.0 to
7.0, but require soils that are free draining. Under waterlogged conditions,
they are susceptible to root rot and mortality is high.
Seedlings are remarkably drought resistant and can survive six
months of hot weather without rain or irrigation. Of more importance, established
shrubs have a remarkable capacity to recover from defoliation. Regrowth
occurs even in the prolonged absence of rain.
Distribution
Chamaecytisus palmensis is endemic to the arid volcanic slopes of La Palma in the Canary Islands. The shrub was introduced to Australia in 1879. It is now also common in New Zealand and has been introduced to parts of Africa.
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Uses: fodder
For centuries, farmers in the Canaries depended on C. palmensis
to maintain their livestock through the long dry summers. However, the
species did not gain international recognition until the 1980s.
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Composition. The foliage has a composition similar to best-quality
alfalfa. Material eaten by grazing animals can be expected to contain 17
to 22% crude protein, depending on the stage of growth and severity of
grazing. The leaves and fine stems of fresh regrowth may contain 25 to
29% crude protein (dry matter) and only 16 to 19% crude fiber. The foliage
is free from toxic substances.
Nutrient composition varies according to soil fertility. In
particular, minerals such as calcium and phosphorus are reduced in foliage
grown on mineral-deficient soils. Leaves have high in-vitro dry-matter
digestibility (0.77 to 0.82). Stem digestibility is lower (0.59), but still
adequate for feeding
(Borens and Poppi, 1986). The fodder contains protein, vitamins and
minerals that are lacking in poor-quality roughage. Used as a supplement,
it increases consumption of dry mature grass and
improves roughage utilization. Normally C. palmensis foliage
is readily consumed by all grazing animals--including rabbits, pigs and
poultry--but there may be some hesitation when it is first
introduced.
Yield. In regions with annual winter rains of 600 to 1000 mm,
established shrubs planted in rows 5m apart can produce 15 to 20 kg of
edible dry matter/plant when harvested once a year. In-row
spacing can vary from 25 cm to 2 m. At a planting density of 1,000
trees/ha, annual yields of 15 to 20 t/ha can be expected (Snook, 1986).
Under current systems of dryland farming in Western Australia, plantations
should produce at least 10 t/ha of edible dry matter from a single annual
grazing or cutting. This is equivalent to 1.5 kg each for 18 sheep every
day of the year. If plantations are harvested three or four times a year,
or subjected to rotational or continuous grazing, yields can be even higher.
Silviculture
Establishment. The small black seeds are extremely hard and must
be scarified or treated with boiling water to ensure quick germination.
Hot-water treatment consists of dropping the seeds into boiling water and
immediately lifting them out. They should not remain in the water for more
than one minute.
In Australia, most plantations are established by direct seeding.
Contractors have developed special machinery to do this in one operation.
A blade or "scalper" removes a strip of surface soil to clear away weed
growth. This is followed by a ripper which opens the soil so that fertilizer
and seed can be placed in lines. Finally, a following wheel compacts the
soil over the seeds.
In most situations, C. palmensis readily makes use of
rhizobia present in the soil. However, to insure nodulation, seed should
be treated with cowpea inoculum or an inoculum specific for the
species.
It is important to apply adequate fertilizer with the seed.
This will encourage deep rooting and the development of robust plants that
can withstand the first summer. Fertilizer should be applied as recommended
for other legumes at each specific site. In most cases soluble phosphate
will be the main requirement, but if additional essential plant minerals
are lacking, these must be supplied. In Western Australia, for example,
superphosphate with copper and zinc should be applied at seeding at a rate
of 200 kg/ha.
Seedlings transplant very well and are commonly used for establishment
in small areas, on steep slopes or where stones prevent the use of machinery.
Animal-proof fences are essential for the first two to three years to protect
young seedlings from grazing animals. Rabbits and hares are particularly
fond of the seedlings and must be excluded. Mature plants recover remarkably
well, even from severe overgrazing, if early regrowth is protected.
Most plantations consist of shrubs planted in parallel rows
about 5 m apart, although distance between rows can be varied. Interplanted
crops grow well because the shrubs provide protection from cold and drying
winds.
Management. Experience shows that shrubs in plantations must
be kept short and bushy. When seedlings are about 10 months old, they should
be cut with a mower or grazed. This encourages the
formation of bushes with multiple stems. The time and frequency of
further harvests or grazing will be determined by the rate of growth. Until
recently, the common practice was to graze or cut
the shrubs once a year. Even when grazing is severe, vigorous leaders
remain, and it is essential to lop these annually.
The need for annual lopping can be reduced or eliminated by
grazing the shrubs three or four times a year or on a continuous basis.
Under such management, vigorous, upright shoots are eaten before they become
too robust.
Obviously, the shrubs must not be overgrazed to the extent that
regrowth is eaten before root vigor is restored. When grazing pressure
is too high, the animals may inflict serious damage by eating the bark.
This problem is rare with good management: It is difficult for the animals
to tear off bark from shrubs with a bushy growth habit and multiple stems.
Fertilizer. For continued high yields of nutritious fodder, regular application of the appropriate fertilizer is essential. In Western Australia, superphosphate and potash (3:2) should be applied annually at a rate of 200 kg/ha. Application of micronutrients, such as calcium, may also be necessary. The shrubs may continue to grow despite a lack of essential minerals but the quality and palatability of the foliage will decline steadily.
Limitations
In Australia, C. palmensis is remarkably free of pests and there is no evidence of viral infection. Slugs, cutworms and grasshoppers eat emerging seedlings, but one application of insecticide at seeding appears to give adequate protection. Mature shrubs are the last crop plants to be attacked by grasshoppers or locusts, and even when all the foliage is eaten, the plants make a rapid recovery when the swarms pass on. The species' requirement for fertilization to maintain high levels of productivity and nutrient content poses a management limitation for resource-poor farmers.
References
Borens, F. and Poppi, D.P. 1986. Feeding value of tagasaste. New Zealand Journal of Agricultural Science. 20:149-51.
International Livestock Center for Africa (ILCA). 1987. Forage Network in Ethiopia Newsletter. Addis Ababa: ILCA, pp. 21-23.
Snook, L.C. 1952. Tree Lucerne: a fodder crop which has been overlooked. Journal of the Department of Agriculture of Western Australia. (3):587-93.
Snook, L.C. 1982. Tagasaste (tree lucerne): a shrub with high potential as a productive fodder crop. Journal of the Australian Institute of Agricultural Science. 48:209-14.
Snook, L.C. 1986. Tagasaste (tree lucerne): high production fodder crop. Shepparton (Australia): Night Own Publishers, 102pp.
Webb, C.L. 1982. Tree lucerne: its taxonomic status and naturalization
in New Zealand. In Tree lucerne in New Zealand. Christchurch (New
Zealand): Division of Scientific and Industrial
Research, pp. 2-5.
A publication of the Forest, Farm, and Community Tree Network
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