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Macadamia integrifolia Maiden & Betche

Macadamia tetraphylla L. Johnson

Proteaceae
Macadamia nuts, Australian nuts

Source: James A. Duke. 1983. Handbook of Energy Crops. unpublished.


  1. Uses
  2. Folk Medicine
  3. Chemistry
  4. Description
  5. Germplasm
  6. Distribution
  7. Ecology
  8. Cultivation
  9. Harvesting
  10. Yields and Economics
  11. Energy
  12. Biotic Factors
  13. Chemical Analysis of Biomass Fuels
  14. References

Uses

Macadamia nuts are eaten raw or after cooking in oil are roasted and salted; also used to make an edible bland salad oil. Rumsey (1927) recommends it as well as a timber tree and ornamental. Years ago a coffee-like beverage known as "almond coffee" was marketed from the seeds.

Folk Medicine

No data available.

Chemistry

Per 100 g, the nut is reported to contain 691 calories, 3.0–3.1 g H2O, 7.8–8.7 g protein, 71.4–71.6 g fat, 15.1–15.9 g total carbohydrate, 2.5 g fiber, 1.7 g ash, 48 mg Ca, 161 mg P, 20 mg Fe, 264 mg K, 0 mg b-carotene equivalent, 0.34 mg thiamine, 0.11 mg riboflavin, 1.3 mg niacin, and 0 mg ascorbic acid. According to MacFarlane and Harris (1981), the oil is high in monounsaturates (79%) and palmitoleic acid (16–25%). The composition ranges from 0.1–1.4% lauric, 0.7–0.8 myristic, 8.0–9.2 palmitic, 15.6–24.6 palmitoleic, 3.3– 3.4 stearic, 54.8–64.2 oleic, 1.5–1.9 linoleic, 2.4–2.7 arachidic, 2.1–3.1 eicosenoic, and 0.3–0.7% behenic acids. The oilcake contains 8.1% moisture, 12.6% oil, 2.6% crude fiber, 33.4% crude protein, and 43.3% N-free extract.

Description

Macadamia integrifolia: Trees up to 20 m tall, with spread of 13 m; leaves opposite in seedings, later in whorls of 3, pale green or bronze when young, 10–30 cm long, margins with few or no spines, petioles about 1.3 cm long; flowers creamy white, apetalous, borne in groups of 3 or 4 along a long axis in racemes, much like grapes; fruit consisting of a fleshy green husk enclosing a spherical seed; nuts round or nearly so, surface smooth or nearly so, 1.3–2.5 cm in diameter; shell tough, fibrous, difficult to crack; kernel white, of uniform quality, shrinking only slightly after harvesting. Fl. June through to March, some strains almost ever-bearing, flowering while fruiting. Macadamia tetraphylla: Trees up to 20 m tall, with spread of 13 m; leaves opposite in seedlings, commonly in 4's rarely in 3's or 5's, purple or reddish when young, margins serrate with many spines, up to 50 cm long, sessile or on very short petioles; flowers pink, in large racemes; fruit consisting of a fleshy green husk enclosing one seed; nuts usually elliptical or spindle-shaped, surface pebbled; kernel grayish; variable in quality and shrinking some after harvest. Fl. between August and October, producing one main crop. Between these two distinct types are numerous intermediate forms varying in spininess of leaves, color of flower, size of nut and thickness of shell.

Germplasm

Reported from the Australian Center of Diversity, macadamias or cvs thereof are reported to tolerate drought, slope and wind. (Duke, 1978). After 1956, Macadamia integrifolia (smooth-shelled type) and Macadamia tetraphylla L. (rough-shelled type) are the names properly applied to the cultivated Macadamia nuts. Prior to this time they had been generally referred to Macadamia ternifolia. F. Muell., a distinct different species, bearing small, bitter, cyanogenic seeds less than 1.3 cm in diameter, inedible and never cultivated. Many cultivars have been developed and grafted trees of promising selections have been made. Three varieties of M. integrifolia, 'Kakea', 'Ikaika' and 'Keauhou', have been planted extensively in Hawaii, all giving satisfactory production under a variety of favorable conditions;. 'Keaau' has been more recently recommended for commercial planting in Hawaii, since it is highly resistant to wind and yields 5–10% more than previous varieties, the entire crop maturing and dropping before end of November. Most of the Australian crop is based upon M. tetraphylla, with some orchards of grafted M. integrifolia varieties. Among the medium-to-thick shelled selections, used mainly for processing, are: 'Richard', 'Tinana', 'Our Choice' and 'Hinde'. For rough-shelled types, mostly grown for table purposes, are: 'Collard', 'Howard', 'Sewell' and 'Ebony'. Varieties showing hybrid characteristics are: 'Oakhurst' and 'Nutty Glen'. 'Teddington' is a hybrid with thin shell. (2n = 28, 36, 56)

Distribution

Native to coastal rainforests of central east Australia (New South Wales and Queensland). Introduced in other parts of tropics, as Ceylon, and commercially grown in Hawaii and France, at medium elevation.

Ecology

Ranging from Warm Temperate Dry (without frost) through Tropical Moist Forest Life Zones, macadamias are reported to tolerate annual precipitation of 7 to 26 dm annual temperature of 15 to 25°C and pH of 4.5 to 8.0. Macadamia grows best in rainforest areas, along coasts with high humidity and heavy rainfall. However, it is tolerant of adverse conditions when once established. Inland, tree thrives in some localities but crops are usually lighter than when grown near coast. Trees produce a deep taproot and relatively few lateral roots; therefore, they need protection of windbreaks in exposed areas. Under orchard conditions, trees are shapely, robust, and more heavily foliaged than they are in rainforest. Grows well on wide range of soil, but fails on infertile coastal sands, heavy clays or gravelly ridges. Yields well on deep, well-drained loams and sandy loams. Slopes steeper than 1 in 25 should be planted on the contour, and every precaution taken to prevent soil erosion.

Cultivation

Propagation by seed is not difficult, but seedlings are variable in production and nut characteristics, and so of little value for commercial plantings. Freshly harvested nuts are best for germination, but require 30–90 days before germination. Propagation usually by cuttings, marcottage and side-tongue grafts. Rootstocks for grafting are readily grown from seed by ordinary nursery means. Grafting in Macadamia is more difficult than in most nut trees due to hardness of wood. Best results obtained when seedling rootstocks are side-wedge grafted with selected scions. After-care of graft similar to that practiced in other trees. Budding is much less satisfactory than grafting. Most suitable time for transplanting young trees to orchard is from February to April in Australia and in Hawaii, when rainfall is good and sufficient soil moisture available. Taproot should be severed about 30 cm below ground about 6 weeks before time to transplant to allow fibrous roots to develop. Roots are very susceptible to exposure and should not be allowed to dry out during transplanting. Grafted trees should be planted with the union well above ground level and watered immediately. Since trees have a tendency to grow tall, young trees when about 75 cm tall, should be topped little by little to produce a few evenly spaced limbs, thus developing a strong, rounded symmetrical tree. Little pruning is required in bearing trees except to discourage leaders, to reduce lateral growth, to let in light, and to make cultural and harvesting operations more favorable. Pruning should be done toward end of winter after crop is harvested. Macadamia grows best in soils with good supply of humus. Farmyard manure may be added and green manure crops can be grown between trees in summer. Under orchard conditions, regular applications of fertilizer are required, as a 8:10:5 formula, at rate of .45 kg per tree per year of age, a maximum of 4.5 kg. Fertilizer should be applied in early spring just before trees make new growth and start flowering. Zinc deficiencies seem to be a problem with this tree, the symptoms being small, yellowish or slightly mottled leaves which are bunched together, crop retardation and poor shoot growth. Condition corrected by application of foliar spray in early spring after first flush of growth, at rate of 4.5 kg zinc sulfate, 1.3 kg soda ash (or 1.7 kg hydrate lime) in 100 gal water. However, spray is effective at any period of year if symptoms are obvious. Since root system is rather close to surface, shallow cultivation for weed control should be practiced. Summer cover crops, as cowpeas, and autumn green manure crops may be grown between trees until harvest time. Grazing cattle on weeds and grass in orchards has the advantage of adding animal manure.

Harvesting

Nuts mature in 6–7 months after flowering and must be allowed to ripen on the trees. Usually the nuts fall to the ground when mature, but in some cvs remain on trees and must be removed with rake. Nuts are picked up from the ground by hand or are raked up. After harvesting, nuts are dehusked, usually with an improvised corn-sheller, washed, placed on wire trays for about 6 weeks to dry out, graded and shipped to market. Machinery for cracking shells has been designed for processing purposes, in addition to several efficient hand-operated crackers, which produce a kernel undamaged. Kernels which are broken during cracking are used by confectioners. Shelled kernels deteriorate rather quickly unless kept in vacuum-sealed jars. Processed nuts when roasted and slightly salted keep extremely well.

Yields and Economics

Most trees begin bearing at 6–7 years, others at 10–15, vegetatively propagated trees bearing earlier. Yield records vary widely. Trees flower for 3 to 12 months, various strains producing fruits over a long period. Some cvs have a definite fruiting season. With great commercial potential in the tropics, macadamia makes an excellent dooryard tree. In addition to production of nuts in Australia, production in Hawaii in 1970 amounted to 5750 tons valued at $.217/lb. Production is being developed in South Africa, Paraguay, Costa Rica, Jamaica, Samoa and Rhodesia.

Energy

According to Saleeb et al. (1973), nuts of M. integrifolia and M. tetraphylla are equal in oil content with an iodine value of 75.4 and 71.8, respectively. They describe a method for partially extracting the oil (6–14% of the weight of intact oven dry kernels), rendering them more attractive, digestible, and less fattening, while diverting 14% of the weight to oil production. Australian estimated yield of about 45 kg/tree annually; in Hawaii, yields average 135 kg/tree. New cvs are known to yield as much as 3.75 MT/ha, averaging 1 ton of kernels, which should contain more than 700 kg oil/ha renewably (oil makes up 65–75% of the kernel).

Biotic Factors

Macadamia trees are attacked by Gloeosporium sp. (Blossom blight) and Macrophoma macadamiae. Nematodes isolated from trees include: Helicotylenchus dihystera, H. erythrinae, and Xiphinema americanum (Golden, p.c. 1984). In Hawaii, the Southern green stinkbug is a serious problem, damaging about 10% of the seed (Monroe et al., 1972)

Chemical Analysis of Biomass Fuels

Analysing 62 kinds of biomass for heating value, Jenkins and Ebeling (1985) reported a spread of 21.01 to 20.00 MJ/kg, compared to 13.76 for weathered rice straw to 23.28 MJ/kg for prune pits. On a % DM basis, the shells contained 75.92% volatiles, 0.40% ash, 23.68% fixed carbon, 54.41% C, 4.99% H, 39.69% O, 0.36% N, 0.01% S, and undetermined residue.

References

Complete list of references for Duke, Handbook of Energy Crops
Last update Wednesday, January 7, 1998 by aw