New intensification project underway

The avocado industry is one of five tree crops, along with almond, citrus, macadamia and mango, set to radically benefit from new research into the possibilities and practicalities of more intensified orchard systems as part of the National Tree Crop Intensification in Horticulture Program (AS18000), funded by the Hort Frontiers Advanced Production Systems Fund, with co-investment from the Queensland Government.

The research is being led by the Queensland Department of Agriculture and Fisheries (DAF), in partnership with the Department of Primary Industries and Regional Development (DPIRD) in Western Australia and the Queensland Alliance for Agriculture and Food Innovation- University of Queensland (QAAFI-UQ). It aims to advance understanding of rootstock and scion combinations, plant density, tree structure, training and pruning options in high and medium density plantings to increase the industry’s potential to broadly adopt more intensive orchard systems.

The five-year research project is comprised of several components. These include both continuing and new studies on existing planting system and high-density rootstock trials located at the Bundaberg Research Facility (BRF).

“It is important to consolidate the findings of previous years (AI13004) by continuing to assess the effects of planting densities, rootstocks and pruning times on maturing orchard systems whilst investigating new options and technologies as part of the current project, AS18000,” Project Leader for DAF, Dr Ian Bally, said.

This new research will investigate carbohydrate and resource allocations in trees, canopy light distribution, and patterns of root density, including its effect on yield, in the established seven-year-old planting systems trial on the BRF. Managing vigour in high density avocado plantings is an ongoing challenge, particularly as trees mature. Further insight into these factors and the relationships between them will build understanding of how avocado trees grow and respond to management under a range of planting scenarios and densities.

A high-density rootstock trial, comparing nine rootstocks, planted in May 2016 at 4.5m x 2m with trees trained to central leaders on a single plane trellis, found when Ashdot was used as the rootstock, trees yielded twice as much as other rootstocks in the first two years of cropping and demonstrated the highest tree-to-tree yield consistency. New research now aims to focus upon issues of excessive growth that creates a low light environment, causing branch death and low yield.

“We will develop our knowledge in how to limit excessive vegetative growth, especially through the use of growth regulator soil drench and tree height limits,” Dr Bally said.

A second high-density rootstock trial, planted in 2018 at 4.5m x 2m on a 3m high trellis, was previously established

Figure 1. Avocado trees under netting near Carabooda, Western Australia.

Figure 2. The project reference group in the orchard.

to investigate eight rootstock/scion treatments (including Maluma Hass and Gem), adding a structural factor to the trial from 2019 (two-dimensional espaliered trees v threedimensional shaping). Evaluation of fruit-set, yield, fruit quality, total light interception, root investigations and architectural studies will continue in this trial through the AS18000 avocado project.

AS18000 will also deliver three new field trials in Queensland and one in Western Australia. The Queensland trials include: 1. a medium density planting using open vase shaping (6m x 3m, 3-4 leaders, 2-3 controlled heights) at BRF, including plant growth regulator product, rate, timing and application methods 2. a demonstration plot at Peirson Farms, also using a medium density open vase shaping 3. high-density trellis planting(s) (4m x 3m) at BRF, including variations of branch structures, pruning timing and nutrition treatments.

Research in Western Australia is focussed on high-density production under shade netting. DPIRD will conduct environmental and plant monitoring over five years to determine the benefits of netting in a trial at Avowest in Carabooda. In this trial, low density planting systems (408 trees/ha) are compared with and without nets, and highdensity planting systems (1,108 trees/ha) are compared with low density planting systems under nets.

The high-density planting will undergo intensive pruning and growth retardant applications to keep the trees under four metres high.

“We hope to demonstrate that the shade netting will result in greater water use efficiency, less fruit drop from hot, dry winds and improved fruit quality by protecting against sunburn and wind rub,” Neil Lantzke, DPIRD’s leader of Vegetable and Horticulture Systems, said.

“The overall tree microclimate should experience higher levels of humidity and we should experience longer growing periods. In terms of the economics, if we have higher yields from high density plantings, this may also justify the effort of netting.”

As well as the in-field research effort, the QAAFI-UQ will undertake functional and structural modelling of selected aspects of orchard planting systems and DAF will evaluate the potential cost benefit of intensified avocado orchard systems. The aim is to compare the feasibility of newly identified production systems with current industry best practice.

A Crop Reference Group comprised of growers, industry advisors and research team members is providing feedback on research activities and findings to guide interpretation and relevance for industry. The project will also conduct frequent field and training events to give industry stakeholders opportunity to engage in the research and experience these innovative management systems for themselves.

More information

For more, contact Bridie Carr, Development Horticulturalist on 0436 675 740 or bridie.carr@daf.qld.gov.au.

Acknowledgement

This is a project of the National Tree Crop Intensification in Horticulture Program (AS18000), funded by the Hort Frontiers Advanced Production Systems Fund, part of the Hort Frontiers strategic partnership initiative developed by Hort Innovation, with co-investment from Queensland’s Department of Agriculture and Fisheries, Queensland Alliance for Agriculture and Food Innovation – The University of Queensland, Plant & Food Research, and the Western Australian Department of Primary Industries and Regional Development, and contributions from the Australian Government.

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