New study reshapes macadamia irrigation

Macadamia farmers hoping for a straightforward estimate of annual irrigation needs may be left wanting after the release of long-term research late last year. Instead of a single benchmark, the findings emphasise the importance of week-by-week, region-specific assessments when scheduling irrigation. The upside is that orchards may require less water than previously assumed.

- Linda Botha

Water requirements for South African macadamias have long been shrouded in uncertainty. As a relatively new crop, limited long-term research applicable to local conditions has been available to guide farmers. Therefore, irrigation scheduling has been based on estimates, with researchers claiming that trees are likely being over-irrigated, leading to added disease pressure.

Compounding the issues that result from over-irrigation is the limited water supply available for the rapidly expanding orchards. The area planted to macadamias has risen from around 6 750ha in 2001 to 81 302ha in 2024, according to Macadamias South Africa (SAMAC). Orchards are expanding into hotter and more water limited regions, while existing farms need to find ways to stretch their water allocation further without compromising yield.

Now, SAMAC has consolidated long-term research conducted in the Mpumalanga regions of White River, the Schagen Valley and Barberton to provide the clearest picture yet of how macadamia trees use water under South African conditions. The guide also highlights where substantial savings can be made.

The guide, titled 'Practical irrigation management for macadamia orchards', shows that macadamias behave differently from many other crops and that irrigation strategies must evolve accordingly. The trials measured tree transpiration, soil evaporation, canopy development, infiltration, deep drainage, and a range of climatic variables to determine how water should be managed for macadamias.

Presenting a webinar on the guide, one of the researchers, Dr Nicolette Taylor, a lecturer in the Department of Plant and Soil Sciences at the University of Pretoria, notes that macadamia producers can sustain high yields without applying more water.

"The key is to apply precision irrigation to enable better use of each drop of water," she says.

UNDERSTANDING HOW MACADAMIAS USE WATER