How to grow macadamia nuts? Cultivation and planting technical regulations of the Yunnan Provincial Institute of Tropical Crops

Macadamia nut orchard

    (III) Soil management
    1. Maintenance of planting strips
    Every dry season, the planting strips should be maintained together with weeding to ensure that the 2-meter-wide strip surface is level and sloping inward, exposing roots and earthing them up, and filling in depressions. On steep slope sections where it is difficult to guarantee the width of the strip surface, the inner wall of the planting hole should be expanded so that the width at the planting hole reaches more than 1.5 m. This not only facilitates field management but also prevents the inner wall from collapsing and harming the plants.    
    2. Weeding
    It is required to keep the area within 30 cm outside the canopy drip line free of weeds. The planting strips should be weeded frequently, and the height of weeds between two successive weedings must not exceed 10 cm. Weeds in the protection strips must be prevented from spreading into the planting strips, and sparse tall grasses and small weeds and shrubs should be cut down at any time. When using herbicides, special care must be taken to avoid the herbicide being sprayed onto or drifting onto the macadamia nut trees.
    3. Green manuring
    Starting from two-year-old trees, green manuring to improve the soil is carried out every year in July to August, when plant growth is relatively slow. Under the canopy drip line, dig a green-manure pit 1 m long, 0.4 m wide and 0.6 m deep. The pits are made in turn on the four sides of the plant, preferably until roots are visible, so as to avoid injuring a large number of roots. Then green manure and decomposed fertilizer are backfilled into the pit in layers until full, which can make the macadamia nut tree develop an extensive root system.
    4. Root-zone mulching
    Every year in November to December, weeds from the planting strips or protection strips are used to mulch the planting strips. Mulching material must never touch the trunk (keep a gap of about 15 cm to prevent termites from damaging the macadamia nut tree trunk), and the mulch thickness should reach 15-20 cm.
    
    (IV) Protecting flowers and fruits
    Macadamia nut has a large number of flowers. According to statistics, a 15-year-old macadamia nut tree produces about 10,000 inflorescences per flowering season, each inflorescence with about 300 florets; however, initially only 6-35% of the flowers set fruit, and ultimately only 0.3-0.4% of the flowers can develop into mature fruit. Macadamia nut young fruit drop is severe; usually 3-8 weeks after flowering, more than 80% of the initial fruit set will fall off by itself. All producing regions around the world are carrying out extensive research on the serious fruit drop problem of macadamia nut to find countermeasures, and certain results have been achieved.
    According to nutrient measurements, supplementing nutrients in advance before the lowest nutrient value appears in the plant body, while taking care to avoid excessive vegetative growth during the fruiting period and preventing severe nutrient competition between vegetative growth and fruit development, plays an effective role in protecting fruit. Macadamia nut fruit grows and enlarges most rapidly before June, and the fruit size is basically set; after that is the process of oil accumulation, so strengthening fruit-protection measures during the young fruit development stage is particularly important. Studies show that using 1ppm-NAA alone can increase the fruit set rate of macadamia nut young fruit by about 35%, but using girdling alone to increase the fruit set rate has no significant effect, and using shoot tipping and top removal measures has no effect. Spraying 0.02% borax, and the use of PP333 and B9 have all been reported to increase yield. Orchards in Hawaii and Australia both use bee release to increase pollination rates, with good effects on increasing yield. Although there is much research in this area, a relatively complete set of methods for promotion and application in field production has not yet been formed.
    
    VII. Harvesting, storage and processing
    (I) Pre-harvest preparation
    1. One to two weeks before the fruit matures and falls (around early August), orchard weeds, dead branches and fallen leaves and other obstacles must first be cleared, and the ground under the canopy leveled.
    2. Methods for determining the harvest period
    The harvest period of macadamia nut is relatively long, lasting from mid-to-late August all the way to mid-October, and the ripening time is related to variety and climate. The inner pericarp of immature fruit is white or light brown; after the fruit is fully mature, the inner pericarp is dark brown and the shell is brown and hard.
   (II) Harvesting and sorting
    After the fruit of macadamia nut matures, it falls to the ground; it is usually collected by hand or machinery. In sloping, uneven terrain or smaller-scale orchards, hand collection is generally used, while larger flat orchards can use mechanical collection.
The harvest interval should be determined comprehensively according to the specific conditions of weather, pests and diseases, rodent damage and labor. Generally, harvest once every 1-2 weeks. In orchards with more serious pests and diseases or in wet weather, the harvest interval should be shortened as much as possible to ensure kernel quality; in dry seasons, if there are few pests, diseases and rodents, the harvest interval can be appropriately extended.
   (III) Dehusking and drying
    1. Dehusking: At present, manual dehusking is mostly used. Fix the fresh fruit and strike it with a wooden mallet, brick, etc. to separate the husk. When striking, the force should be controlled well to avoid cracking the shell. This method is only used in small-scale plantations. With the development of the macadamia nut industry, large quantities of fresh fruit are dehusked by mechanical methods. After dehusking, move the husks to a place far from processing equipment and work sheds for composting, remove all unsound in-shell nuts and burn them regularly.
    2. Screening: After dehusking, the in-shell nuts must have impurities, husk fragments, pest- and disease-damaged nuts, sprouted nuts, cracked nuts (except those with only tiny cracks), etc. removed as soon as possible. In addition, to ensure the kernel recovery rate, fruits that are smaller in size and have a lower kernel recovery rate must also be screened out.
    3. Drying and storage: After macadamia nuts are dehusked, if they are piled up in large quantities, high temperature and high humidity will cause the fruit to mold, which in turn will cause the kernels to become rancid, causing major losses, so drying must be carried out as soon as possible. For small-scale orchards with not many nuts, a simple drying method is to spread the fruit on wire mesh racks in a shaded, well-ventilated place at a thickness of 10-25 cm, rake and turn once a week, and it takes about 6 weeks to complete drying. This natural air-drying method dries to a minimum moisture content of 10%. When the moisture content reaches 10%, nearly half of the nuts will rattle when shaken. In large-scale macadamia nut production, artificial drying is generally used.
    It is worth noting that in-shell nuts must never be exposed to the sun, otherwise the shells will crack, which can easily cause the kernels to become rancid, causing kernel quality to decline rapidly and lose their usable value.
    
    (IV) Grading
    Dry the in-shell nuts at low temperature to a moisture content of about 1.5%, separate the kernels from the shells by manual or mechanical methods, and then further grade the kernels. Grading generally uses the water flotation method: place the kernels in clean water with a density of 1.000 kg/L for water separation. Those floating on the water surface are first-grade kernels, with an oil content of ≥72%, plump and light-colored kernels, smooth bases, bright brownish-yellow after roasting, crisp texture, and a mild nutty aroma. Put the kernels that sink in the water into salt water with a density of 1.025 kg/L; those that float up are second-grade kernels, with an oil content of 66-72%, slightly shrunken and slightly black kernels, unstable processing quality, a tendency to go off-flavor, and a soft texture. The rest are third-grade kernels, with little usable value. Kernels after water treatment should be dried and stored as soon as possible to maintain the flavor of the nuts.     (Contributed by the Provincial Institute of Tropical Crops)