Carbohydrates in macadamias (Agri Technovation)

Chantal Forssman

By Riaan Brümmer
Senior Agronomist

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Have you ever walked through your macadamia orchard and noticed that trees in one block had more nuts than those in the block next to it, or, on a smaller scale, that some trees within one block were “dripping” with nuts while neighbouring trees had no nuts to show?

This occurrence could be caused by a number of different factors such as the soil type, soil nutrient status of the soil, tree health, pruning practices followed, fertiliser applications, mois- ture content etc. There is however one similar- ity amongst all these factors which is the fact that they all impact the carbohydrate levels of the trees.

What are carbohydrates?

Carbohydrates are the product of photosynthesis, the process where the leaves of trees produce soluble sugar in the form of sucrose (sugars) and starch. Within the context of carbohydrates, leaves are referred to as a carbohydrate source.

Carbohydrates perform numerous roles in trees. They are necessary for the growth of tree organs such as roots and vegetative shoots and support the development of reproductive flowers or nuts, amongst others. A shortage of carbohydrates could result in poor flowering and fruit set and a lack of root and vegetive shoot growth. In short, carbohydrates are essential for plant growth and production throughout the season.

Carbohydrate sugars are readily available, provide immediate energy to plants and can be transported over long distances in the phloem. Carbohydrates in the form of starch are stored in the tree as reserve energy. Sugar carbohydrates can be made available from these stored carbohydrate reserves when sugars are limited.

Measure and monitor carbohydrate levels

It is therefore important to know the carbohydrate status of your trees for the effective management of carbohydrates and production.

Agri Technovation now offers the ITEST™CARBOHYDRATES analysis as a service, making it possible for producers to measure and know the carbohydrate status of their trees, which in turn assists producers with the timely development of management practices aimed at ensuring optimal plant growth and annual produce. Agri Technovation has now established carbohydrate norms in specific phenological phases for macadamias. We believe that our carbohydrate analysis gives the producer a glimpse into the near future of their macadamia orchards.

Nutrients and Carbohydrates

When it comes to nutrients, producers gene- rally know and understand the basic role NPK fertilisers fulfil in plants. The specific impact of these fertilisers, however, on carbohydrates, in particular, is not always understood. Not only do these fertilisers have a very specific impact on the particular carbohydrates, but also on the rather complex carbohydrates production and transport process.

From our experience, leaf and root samples are the best indicators for the ITEST™CARBOHYDRATES analysis as they are regarded as the plant structures most important for producing and storing carbohydrates.

Comparison of the annual mineral leaf samples with ITEST™CARBOHYDRATES analysis results, is an excellent way to determine a limiting factor namely prohibiting the production or transport of carbohydrates.

In the scenario referred to below (April 2022), a mineral leaf sample was taken in a fully producing macadamia orchard and a carbohydrate sample was taken on that exact GPS point.

The analysis results indicate that the level of the nutrient magnesium (Mg) is below the minimum optimum norm.

To understand the impact of this, the role of Mg in a macadamia tree must also be understood. A primary function of Mg is that it is the central atom of the ring structure in the chlorophyll molecule, and therefore very important for optimum photosynthesis and the production of sugars (energy). Magnesium and potassium (K) are also responsible for transporting sugars into the phloem from the mesophyll cells, where they will be utilised by one of the many carbohydrate sinks of a macadamia tree.

Macadamia crops are prolific flowering tree crops, where thousands of racemes emerge from buds in spring (mostly). Each raceme can hold up to 800 flowers and only ±0,0004% set as harvestable nuts (The Macadamia magazine). To support these high-energy activities effectively, the trees require very high levels of carbohydrates to provide sufficient energy to the trees.

Also, macadamia nuts have a very high oil content, up to 69 to 78%, and therefore re- quire sufficient energy (carbohydrate sink) to support the process of filling these nuts with top-quality oil. (Amaral et al., 2003; Kaijser et al., 2000; Miraliakbari and Shahidi, 2008a, 2008b; Robbins et al., 2011; Wall, 2010.)

Manage your carbohydrates effectively

Thus, it is important to measure and replenish where necessary the carbohydrates with op- timum nutrition and manipulation during the flower initiation phase, as this will ultimately determine whether a bud is vegetative or reproductive.

At Agri Technovation we recommend a com- prehensive fertiliser programme to manage carbohydrate levels effectively, combining a soil-applied fertiliser with a post-harvest energy foliar spray which consists of the products NUTS-TO-GROW™, TRY ME™, ZINC PHLOEM™ and any other nutrient deficiency indicated by the above analyses.

Product registration numbers: NUTS-TO-GROW™ – K9551; TRY ME™ – K9552; ZINC PHLOEM™ – B5734

The bigger picture

At Agri Technovation we are focussed on ensuring that the producer has the necessary tools and information required to make in- formed decisions with in-season monitoring of carbohydrates and mineral levels. Together with the vast number of other services we offer, all supported by our cloud-based platform MY- FARMWEB™, we are able to provide effective nutritional advice tailored to every producer’s particular needs.

Ultimately, it is of critical importance to manage your macadamia trees’ carbohydrate levels, as this is the only produce manufactured by a plant through its phenological cycle that is able to support the demand of the crop (provide sufficient energy).

Macadamia trees in full bloom. Photo: Riaan Bümmer.