Custard apples grown on trellis wires have certain advantages over traditional vase shaped trees when it comes to orchard maintenance and for North Coast growers Lukas and Melissa Van Zwieten the choice to build their new orchard this way has paid off. The exposed location meant that a trellis system will help protect trees from wind damage, and they also facilitate easier harvesting and disease management.
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Growers from the Northern Rivers and Queensland's Sunshine Coast were recently given a tour of one of the most modern farms, prepared and executed by the Van Zwietens on a ridge of red soil above Teven via Ballina.
In keeping with his day job as a soils researcher and adjunct professor at Southern Cross University, he designed the orchard as if it was part of a trial plot, with marked row numbers and different management regimes for separate localities.
He employs a part-time farm manager to oversee the operation.
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The farm was a virtual blank slate when the family moved onto it eight years ago. It had a fairly long history as a cattle grazing property, and areas not under orchard are still running a small herd. Soil carbon levels in the orchard, under pasture and in remnant rainforest are around 10 per cent, giving these soils a distinct brown colour, indicating the managed ferrosols on the property are at their upper limit of being able to carry any more carbon.
"The extremely high carbon levels help drive mineralisation or organic matter in our soils so we have no problem with nitrogen," says Dr Van Zwieten.
Fruit split in winter, potentially attributed to calcium deficiency, was addressed through the addition of gypsum, which has helped to increase the exchangeable calcium from 20mg/kg up to 70mg/kg. But "more work is still needed here to minimise harvestable fruit loss due to splitting" he says.
The business plan written by Lukas and Melissa for custard apples also considered passionfruit and macadamia production. In fact, while waiting for new grafted stock they experimented with figs, grown on trellis wires too, but admits these "remain on probation", because of the difficulty in harvesting fruit easily split during warm and humid months. As if to make good his threat three rows were recently removed to take new custard apple stock of the KJ Pink variety - chosen as they are best for a trellis system.
After the last of the fruit were picked in spring, trees were given a harsh prune which will be followed in January by tipping and stripping of leaves to encourage late flowering and late fruit set. Different rows are given different levels of intervention.
By tipping and stripping the trees, the Van Zwietens have been able to extend their picking season into October, taking advantage of off-season prices. Their last pallet of fruit sold in early October for up to $90 a tray.
"That's the advantage of pushing out our harvest window," Dr Van Zwieten said. "We compromise yield by heavy mid-season pruning, tipping and stripping, even though we are careful with the flowers, but by doing this we are maximising profit."
Some growers commented that tight harvest windows offered by vase-pruned trees were better able to take advantage of scarce labour, so there was some trade-off between the two management types.
The Van Zwietens were influenced by Phil and Patti Stacey' pioneering work into trellised trees. A point of difference on this farm is that end posts are replaced with lengths of flexible chain cast into poured cylinders of concrete, flush with the ground. The structure stands up to significant winds coming off the Pacific Ocean, 140 metres below.
The first wire is well off the ground and carries an irrigation pipe with a swing arm mower to be employed managing the inter row and under the row, reducing herbicide use and encouraging inter-row cover crops like white clover, which is blooming well this season and contributing legume-nitrogen into the orchard system.
Lukas said they worked hard to force the trees' first lateral limbs onto the bottom wire.
"We were brutal in training them," he said. "We didn't allow the upper laterals to develop until the bottom lateral was well established."
Several trials are taking place on the farm, the oldest trees of which are at 4.5 years. Eventually 1200 trees will be strung up on trellis wires.
With Dr Van Zwieten best known for his research on biochar - and a paper printed in the prestigious Nature Communication journal last month - it comes as no surprise that the farm carries three lots experimenting with inputs of char made from either rice husk, wood or poultry manure.
"We have a good trial set-up, but we need analysis," said Dr Van Zwieten, intimating that the field is open to student or post graduate work.
