Macadamias cannot tolerate poor nutritional conditions. The first signs of nutritional deficiencies are a typical reduction in production, and then a gradual decline in the condition of the tree, with fewer and sparser leaves. Eventually branches will begin to die back in severe cases of malnutrition, and this causes damage due to sunburn on exposed branches and stems.
Fertilisation of macadamias must basically ensure that the tree grows in well structured soil with a water pH of between 5 and 5.5.
The levels of N, P and K should be supplemented as they are utilized by the tree (removal by harvesting included), and trace element contents should be measured and supplemented.
Typical Macadamia NPK is : 15-5-20+S+B+Zn . K2O source is recommended to be 100 % SOP.
Boron is important
After Phosphorous, Boron is probably the most important element in macadamia nutrition. Boron is responsible for cell division, pollen germination, transportation of carbohydrates through cell walls and the translocation of hormones in the plant. Flower and fruit parts are particularly sensitive to Boron deficiency.
Zinc plays a major role in the fertility of the female parts of the macadamia flowers. Zinc is also needed for new growth and it plays a role in phosphorus metabolism and in the regulation of the use of water.
Zinc deficiencies are usually exacerbated by high P applications that are typical of macadamias. In the spring and early summer, problems can develop when trees are growing quickly, but when zinc is not readily absorbed because of low soil temperatures.
Zinc deficiencies cause:
• Delayed or arrested growth as a result of low levels of auxin in the tissues.
• Bunching of the terminal growth of offshoots and buds, resulting in small, underdeveloped leaves.
• Abnormal root thickening.
• Pale yellow colour of new growth. From close by, the veins are green while the rest of the leaf appears to be pale yellow or white (chlorotic).