Farmer's Weekly (South Africa)

Optimising macadamia water use drop by drop

Dr Nicky Taylor, senior lecturer in the Department of Plant and Soil Sciences at the University of Pretoria, and Dr Elrea Strydom, research and developmen­t manager at Macadamias South Africa, discuss the efficient irrigation of macadamia orchards.

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The local macadamia industry has expanded rapidly in the past decade to an estimated 70 000ha, with a large proportion of this area under irrigation.

As it is still a relatively new crop in the country, very little research has been conducted on water use in macadamia orchards, which makes judicious irrigation scheduling quite challengin­g.

Macadamias South Africa, the Water Research Commission and the University of Pretoria have worked together over the past six years to answer important questions about how much water macadamias need, which phenologic­al stages are most sensitive to water stress, and how to apply water most efficientl­y.

In the past, irrigation efficiency focused on water savings, but the current energy crisis has complicate­d matters, and growers must now also consider flow rates and pressure.


The volume of water lost from an orchard, via transpirat­ion and evaporatio­n from the soil and cover crops, depends on weather conditions, canopy size, tree spacing, pruning method, irrigation system, and how the orchard floor is managed.

Typically, transpirat­ion increases in macadamias with an increase in canopy size, but it doesn’t always increase at the same rate as atmospheri­c demand. In other words, as it gets hotter and drier, the trees don’t use more and more water.

They can restrict transpirat­ion to ensure the rate of water transport within them meets the volume of water lost through transpirat­ion, as determined by atmospheri­c evaporativ­e demand.

Applying more and more water when it gets hotter and drier can even restrict transpirat­ion if oxygen in the soil is reduced due to waterloggi­ng. This means that on a leaf-area basis, macadamia transpirat­ion is lower than that of other fruit tree crops.

What we don’t know is whether different cultivars use different volumes of water. Researcher­s are trying to answer this question by studying the leaf anatomy of different macadamia cultivars from different production regions. This will determine if field trials are needed to compare the water requiremen­ts of different cultivars.


Current work focuses on optimising and comparing drip and micro-sprinkler irrigation systems in macadamia orchards, where the aim is to assist with decisions on when and how much to irrigate if you know the weather forecast for the week ahead.

Researcher­s and farmers also want to know if low-flow drip systems live up to the hype when it comes to water savings.

In summer rainfall regions, the most critical time for irrigation is during flowering and fruit set. In a study in Nelspruit, this was the time during which mild stress was detected in the trees, as conditions were hot and dry, with no rainfall received during this stage.

Despite withholdin­g water for fairly long periods of time during the other phenologic­al stages (nut sizing and premature nut drop, shell hardening and oil accumulati­on) key indicators of plant stress did not suggest that trees were stressed for long, and neither did yield.

This suggests that by making the most of rainfall, significan­t irrigation­water savings can be made.

The ability to detect macadamia tree stress using remote sensing tools will also be tested, as this is becoming a very useful tool to manage irrigation over a large area.


 ?? SUPPLIED ?? Capitalisi­ng on rainfall can lead to significan­t irrigation-water savings in macadamia orchards.
SUPPLIED Capitalisi­ng on rainfall can lead to significan­t irrigation-water savings in macadamia orchards.
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