Macadamias

Improving Crop Quality and Kernel Recovery

**** most signification, * least significant

Macadamia Nutrient Products

Nitrogen (N)

Too much nitrogen, or nitrogen applied at the wrong time of the year, will stimulate excessive vegetative growth at the expense of kernel recovery and nut quality. Nitrogen needs to be applied in small amounts regularly.

Phosphorus (P)

Availability may be impaired due to the reactivity of phosphorus with some soil elements, especially Iron (Fe). This is a feature of macadamia production on Red Krasnozem soils (typical of much of the far northern New South Wales production area).

Potassium (K)

Deficiencies can occur under conditions of nutrient imbalance, and may lead to defoliation and tree decline. Potassium availability will also be diminished by inappropriate nutrient management regimes, e.g. if the exchangeable nutrient pool is dominated by calcium and/or magnesium, the availability and uptake of potassium will be impaired.

Sulphur (S)

Many fertilizers (including superphosphate, potassium sulphate, and potassium thiosulphate) and soil amendments (gypsum, i.e. calcium sulphate) provide sulphur as a component of the product. Because of the sulphur contribution by fertilizers, deficiencies are rarely seen in macadamia culture.

Calcium (Ca)

Movement of calcium into macadamia tissue from the soil may be adversely affected by several factors, including excessive nitrogen or potassium fertilization, conditions of plant stress (dry soils, hot weather), or heavy pruning.

Magnesium (Mg)

Deficiencies can occur in trees growing on acid leached soils with low levels of organic matter, or they can be due to excessive fertilizer use, heavy liming, dry weather and heavy crop loads.

Zinc (Zn)

Early Spring conditions of rapid growth and cool soils may make it difficult for trees to absorb sufficient zinc. Growth is restricted, which can cause terminal shoot dieback.

Boron (B)

Some cultural practices, including over-fertilization and activities leading to soil compaction or root damage, may contribute to boron deficiency. Boron is not readily moved within plant tissue, and a deficiency will affect new growth in the tree, including pollination and nut development. Care must be taken when applying boron, as over-supply can lead to Boron toxicity.

Soil pH

pH measures the relative concentration of hydrogen ions in the soil solution, and it is a log scale number. This means a pH of 5 is ten times more acidic than a pH of 6, and a pH of 4 is 100 times more acid than pH of 6. Below a pH of ~4.5, some elements, in particular molybdenum, copper and boron, become unavailable to the plant. The desirable range for macadamias is 5.0-5.5 in Calcium chloride solution.