Publication
from Agroforestree Database: a tree reference and selection guide
version 4.0
by C. Orwa, A. Mutua, R. Kindt, R. Jamnadass and S. Anthony
Macadamia
integrifolia Maiden
et Betche
Local Names:
English (smooth macadamia nut, Queensland nut, macadamia nut,
Australian bush nut)
Family:
Proteaceae
Botanic
Description
Macadamia
integrifolia is a large, spreading, evergreen tree
attaining a height of 18 m and a crown of 15 m.
Leaves
in whorls of 3, oblong to oblanceolate, 10-30 x 2-4 cm, glabrous,
coriaceous, irregularly spiny-dentate when young, entire in later
stages; petiole 5-15 mm long; 3 buds arranged longitudinally in the
axil of each leaf usually only the top bud shoots out, making a sharply
acute angle with the trunk.
Racemes axillary on mature new
growth or on leafless older shoot, pendulous, 10-30 cm long, with
100-500 flowers; flowers in groups of 2-4, about 12 mm long,
creamy-white; pedicles 3-4 mm long; perianth tubular with 4 petaloid
sepals.
Fruit a globose follicle, 2.5-4 cm in diameter; pericarp
fibrous, about 3 mm thick. Seed (nut) usually 1, globular, with a
smooth, hard, thick (2-5 mm) testa enclosing the edible kernel.
The genus is named after J. Macadam (1827-1865), secretary of the
philosophical Institute of Victoria. The specific name integrifolia is
from the Latin integri-‘entire’ and folium-‘a leaf’ in allusion to the
grouping of leaves in whorls of four.
Biology
Floral initiation
takes place when temperatures drop and trees become quiescent in
autumn, the optimum temperature being 18 deg. C. The initials remain
dormant for 50-96 days; the racemes extend after a rise in temperature
and some rain. In Australia high yields are associated with a strong
and early spring flush before anthesis, followed by minimal shoot
growth throughout the 6-month nut development period. At the end of nut
development, there is a late summer flush; meanwhile nuts may be
retained on the tree for a further 3 months, but gradually they fall.
The
flowers are protandrous, the anthers dehiscing 1-2 days before
anthesis, whereas the stigma does not support pollen tube growth until
1-2 days after anthesis.
Pollination is by insects; most
cultivars are at least partly self-incompatible. Planting pollinator
trees and introducing bees are important for good fruit set. Fruitlets
continue to be shed up to 2 months after bloom.
Ecology
M.
integrifolia
prefers well-drained soils, shelter from winds and a mild, frost-free,
subtropical climate with well-distributed annual rainfall of at least 1
200 mm. It occurs naturally in the fringes of subtropical rainforests.
It appears to tolerate only a narrow range of temperatures (optimum
during the growing season is 25 deg. C). Temperature is the major
climatic variable determining growth and productivity. Trees in
Southeast Asia grow fairly well but flower and fruit sporadically
throughout the year. In eastern Africa, orchards are planted at
elevations of 1 000-1 600 m in areas with a prominently seasonal
climate, leading to a synchronous resumption of growth and flowering
over a cool, overcast season. Abnormal tree growth, low yield and poor
nut quality have been noted in Africa at higher altitudes with little
sunshine during the flowering and fruiting season.
The
xerophytic characteristics of the tree, including the sclerophyllous
leaves and proteoid roots (dense clusters of rootlets formed to explore
poor soils low in phosphorus) suggest adaptation to relatively harsh
environments. However, the conditions required for optimum production
may be quite different from those for survival. Mature M. integrifolia is
capable of withstanding mild frosts, but only for short periods. The
brittle wood makes trees susceptible to wind damage.
Biophysical
Limits
Altitude: 0-1 600 m, Mean annual temperature: 15- 25 deg. C, Mean
annual rainfall: 700-3 000 mm
Soil type: M.
integrifolia
can be grown in a wide range of soils including poor soils, but not on
heavy, impermeable clays and saline or calcareous soils. It is most
suited to deep, well-drained loams and sandy loams with good organic
matter content, medium cation exchange capacity and pH of 5-6.
Documented
Species Distribution
Native:
Australia
Exotic:
Brazil, China,
Colombia, Ethiopia, Fiji, Guatemala, Indonesia, Kenya, Malawi, Mexico,
Peru, Samoa, South Africa, Tanzania, Thailand, US, Venezuela, Zimbabwe
The
map above shows countries where the species has been planted. It does
neither suggest that the species can be planted in every ecological
zone within that country, nor that the species can not be planted in
other countries than those depicted. Since some tree species are
invasive, you need to follow biosafety procedures that apply to your
planting site.
Products
Food:
The fine, crunchy
texture, rich cream colour and delicate flavour make the macadamia nut
one of the finest dessert nuts. The eating quality of the nut is
enhanced by lightly roasting it in coconut oil and salting. Raw kernels
are also popular alone or in a wide range of confectionery and
processed foods. The quality of the kernel is related to its oil
content and composition. Nuts are mature when the kernels accumulate
72% or more oil, as determined by specific gravity. Kernels also
contain 10% carbohydrates; 9.2% protein, which is low in methionine;
0.7% minerals, particularly potassium;, and niacin, thiamine and
riboflavin.
Apiculture: Macadamia
pollen is very attractive to bees, providing necessary forage for honey
production.
Macadamia shells may be used as fuel, generating sufficient energy to
dry wet, in-shell nuts.
Shade or
shelter: M.
integrifolia makes an excellent evergreen shade and
shelter due to its thick crown of leaves.
Tannin or
dyestuff: The hulls, the green covering of the
nuts, contain approximately 14% of substances suitable for tanning
leather.
Lipids: Macadamia
is the richest oil-yielding nut known. The kernel contains more than
75% oil, suitable for human consumption.
Essential oil: The
characteristic, subtle macadamia flavour is probably due to volatile
compounds, the major ones being similar to those in other roasted nuts.
Services
Ornamental: As
well as being an evergreen nut-bearing tree, M. integrifolia
has good symmetrical shape and when in full bloom is covered with
creamy-white and pinkish flowers in long, narrow, drooping racemes.
These make it a popular ornamental tree.
Soil improver: The
decomposed husk is commonly used in potting soil.
Intercropping: Inter-row
cropping can be practised with trees such as citrus, if they are
removed at 12 years. Macadamia will retard the growth of papaya planted
near it.
Tree
Management
M.
integrifolia
comes reasonably true to type when raised from seed. Seeds for
propagation are selected from vigorous, heavy-bearing trees. The fresh
nuts are planted with no pretreatment.
Grafting may develop
desirable clones; side wedge grafting has been used exclusively in
Hawaii. Other vegetative propagation methods include splice grafting
and cuttings.
Seedling growth, initially slow, gathers momentum
as saplings produce a series of extension growth flushes in a year. The
juvenile phase lasts for 7 years or more, but grafted trees come into
bearing after 3 years. The current trend is for high-density hedgerow
plantings, which maximize early yields. Inter-row spacing of 10 m is
most common (7 m if mechanical pruning is carried out). The distance
between rows should be 4-6 m, depending on cultivar and growing
conditions.
Correct branching should be induced at an early
age after which there should be no further pruning. During the first 2
years, training (a form of corrective pruning) is done to develop a
strong, well-balanced framework for future growth. The young trees
should receive careful attention with respect to irrigation, weed
control and frost and wind protection. They should also be fertilized
to make them grow well and induce early flowering.
Mulching is
recommended for young trees (when the trees come into bearing, it
interferes with nut collection). Fertilizer management should be guided
by leaf and soil analysis, the phenological cycle and yield. Macadamia
trees appear to be sensitive to nutrient deficiencies and imbalances,
and positive responses to N, P, K, Zn, B, S, Mg, Fe and Cu have been
observed.
Yields of 45 kg nuts-in-shell from better trees or an average of
3.2-3.5 t/ha per year are obtained in Hawaii.
Germplasm
Management
Seed storage behaviour is uncertain. Drying until the kernel rattles in
the shell does not harm viability; no loss of viability during 4 months
of storage in paper bags at room temperature, after which time
viability is reduced, and none survives after 12 months. No loss in
viability after 12 months of storage in polythene bags at 12 deg. C;
viability maintained for 24 months with partially dried seeds at 15
deg. C.
Pests and
Diseases
In their
place of origin macadamias are attacked by more than 150 pest species,
although parasites and predators usually provide considerable control.
Insects that commonly reduce yields include macadamia flower
caterpillar (Homoeosoma
vagella), fruit spotting bug (Amblypelta nitida),
banana spotting bug (A.
lutescens), macadmia nutborer (Cryptophlebia ombrodelta),
and macadamia felted coccid (Eriococcus
ironsidei). Any of these have the capacity to destroy much
of the crop during severe infestations. The macadamia twig-girdler (Neodrepta luteotacetella)
and macadamia leafminer (Acrocercops
chionosema)
destroy foliage and may therefore reduce yield indirectly. Many of the
minor macadamia insect pests cause damage sporadically. Rats are
particularly fond of macadamia nuts and can be a problem in some areas.
In comparison with other fruit trees, relatively few diseases are
serious in macadamia.
Further
Reading
Allan P. 1969. Macadamia production overseas. Farming South Africa.
45(2):29-32.
Cann HJ. 1965. The macadamia: Australia’s own nut. The Agricultural
Gazette. 76(2):78-84.
Doran
CJ, Turnbull JW (eds.). 1997. Australian trees and shrubs: species for
land rehabilitation and farm planting in the tropics. ACIAR monograph
No. 24, 384 p.
Hong TD, Linington S, Ellis RH. 1996. Seed storage behaviour: a
compendium. Handbooks for Genebanks: No. 4. IPGRI.
Lemmens
RHMJ, Soerianegara I, Wong WC (eds.). 1995. Plant Resources of
South-east Asia. No 5(2). Timber trees: minor commercial timbers.
Backhuys Publishers, Leiden.
Robinson JC. 1966. The macadamia nut tree. Hortus. 6:4-6.
Tonks EP. 1968. The macadamia. Shell Farmer. 11(3):1-8.
Verheij
EWM, Coronel RE (eds.). 1991. Plant Resources of South East Asia No 2.
Edible fruits and nuts. Backhuys Publishers, Leiden.
Wickens GE (ed.). 1995. Non-wood forest products 5; Edible nuts. FAO,
Rome.
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