Using netting to improve productivity and the environment in tree crops

The trial started in 2021 and is being run by the Department of Agriculture and Fisheries (DAF) with Macadamia Farm Management (MFM). The aim is to find out if netting can help with:

• retaining mulch
• improving soil structure and moisture retention.

Macadamia nuts are generally harvested using a sweeper, or finger wheel, which runs underneath the tree's canopy, brushing the nuts out to be collected by machine. While efficient, the process tends to remove the valuable mulch, made up largely of fallen leaves, which help protect the tree's root system and soil biodiversity.

The idea of the netting is to deflect the falling nuts toward the interrow, increasing machinery harvesting effectiveness.

The trial is using PVC pipes with mesh stretched across these frames, positioned on an angle from about 30cm off the ground at the lowest point, up toward the tree trunk, about 20cm higher. The netting runs for about 250m.

PVC has been chosen for the frames as timber would rot from the moisture and shade, while steel would rust due to the same conditions (particularly in coastal orchards). The trial is currently under trees which are 34 years old, and the netting is mostly shaded.

In a similar trial in the Gympie region a few years ago, DAF found:

• nut yields improved by an average of 20% for the netted trees
• soil organic matter increased by 50%, with the weight of the roots around the trunks also increasing.

Toward better sustainability

Macadamia nuts fall over a 4-month period and a harvest is taken every 3 to 4 weeks depending on weather. That can mean significant traffic up and down orchard rows.

When the nut is lying on the ground it gets moist and dry, causing discolouration of the kernel. Nuts are also subject to mould when they are lying on the ground, so keeping nuts off the ground helps to preserve their appearance and quality. High quality, blemish-free nuts attract a premium price with processors.

As well as improving the quality of the harvest, the netting system helps to reduce soil compaction. The less machinery wheels going near the base of the tree, the better. Less compaction benefits the soil structure and has long term benefits in reducing soil erosion and run off, thereby helping to improve reef water quality.

An industry perspective

Scott Allcott, Director at Macadamia Farm Management, said they were involved with the trial to find out about more sustainable farming systems. With the cost of water and diesel, industry is looking for ways to stretch water and organic matter further, and potentially apply less synthetics.

The under-tree netting trial is already showing benefits. The soil is not as compacted or disturbed as previously, with less machinery being used close up to the trees. Researchers are monitoring the organic matter below the trees to see if it is increasing and irrigation can be reduced.

The trial has another 3 years to go, with the results being fully analysed and available in 2026. If the benefits are there, it is hoped they will be fully implemented by the macadamia industry.