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Small Nuts
When trees continue to suffer with “small nuts”, what are the likely causes?
Typical Signs & Symptoms
Field symptoms of small nuts are not generally evident in the orchard and are only measurable after husking, where there are excessive numbers of nuts less than 19mm in diameter.
Comments
From a nutritional perspective, small nuts may be caused by inappropriate applications of nitrogen and potassium and to a lesser extent boron. Nitrogen is required throughout the year with the peak demand period being in the mid-Sept to late Nov. period (see comments under Shell/Nut Ratio). It is important to note that adequate nitrogen must be present at or before flower set. Again, leaf tissue testing will assist in determining the correct application levels. Potassium granular fertilizers are usually supplied as either potassium chloride, (muriate of potash), or potassium sulphate. The chloride form is a cheaper source of potassium, but as macadamias are sensitive to chloride salts and potassium chloride has a salt index of 116 (2.5 times that of potassium sulphate, salt index of 46), using the muriate form will add to the overall salinity of the groundwater system. It is therefore strongly recommended that potassium sulphate be used on macadamias. Lower salinity will result in more potassium being ‘carried’ (translocated) into the plant tissue and nuts due to the increased flow of moisture. This translocation process is also assisted by boron, which helps with tissue development and carbohydrate metabolism.
Treatment, Timing & Application
Around 550g of nitrogen per tree should be applied over the year with about one third of this applied mid-Sept to late Nov. and the balance over the period mid-Feb to mid-Sept. Note that excessive nitrogen use will affect kernel recovery (see Shell/Nut Ratio) The nitrogen is applied as Calcium Ammonium Nitrate (CAN) and in dry granular blends such as Paton Macadamia Blends 212 and 418 (see comments under Shell/Nut Ratio and Nut Drop). Potassium around 500g per tree in the sulphate form will be supplied as part of Paton Macadamia Blends 212 and 418, or as part of a special blend based on soil tests. However, it is important that potassium be available as the nuts expand. Ground applied Liquid K & S (potassium thiosulphate) and a potassium foliar application such as Paton Macadamia Liquid Fertilizer M2 are helpful, especially in times of dry weather.
Rates should be determined by leaf and soil analysis.
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