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Ongoing project

Almond productivity: Tree architecture and development of new growing systems (AL14007)

Key research provider: Plant & Food Research Australia

What’s it all about?

Established in 2014 and due for completion during 2019, this project is being conducted as part of a coordinated research program into boosting almond productivity and profitability. It has a specific focus on tree architecture and the development of new, high-density growing systems. 

This project has a number of ongoing field trials involving pruning, trunk girdling and light management, and evaluating different cultivar characteristics. It has developed significant momentum with field trials attracting international attention and with more growers considering the adoption of new high-density growing systems.

There are a number of areas of investigation, including …

Commercial high-density trials

Management systems for new almond orchards planted at high density are continuing. In long-term trials planted in July 2018, two self-fertile almond varieties (Shasta and Vela) budded on Nemaguard rootstock are being evaluated at four planting densities. The first commercial crop is expected in the 2019/20 season.

Pruning responses – new cultivars

This medium-term trial planted in July 2018 will evaluate a range of pruning and nursery management techniques to produce central leader Nonpareil, Maxima, Carina, Vela and Shasta trees suitable for high-density plantings. All trees were budded on Garnem rootstock with two sets of trees budded in early-December 2017 and mid-January 2018, and a third set ‘dormant budded’ in May 2018 to produce a range of tree sizes (large, medium and small, respectively) for field-planting in winter. The first commercial crop is expected in the 2019/20 season.

Different tree sizes were added to the program because the team has found strong seasonal differences in the size and calibre of trees produced by nurseries, and growers need to know how to work with smaller trees, developing a strong central leader with minimal input in terms of pruning and training.

Natural tree architecture studies

The team is working with breeders to speed identification, breeding and commercialisation of almond cultivars with architectural features associated with high productivity that are suitable for planting in high-density orchards.

In a series of short-term studies, desirable architectural traits will be identified in current and future almond cultivars starting with unpruned trees in their first leaf budded onto clonal rootstocks. By not heading the trees at planting and not pruning or selecting limbs, the true natural growth habit of the cultivars can be observed. New cultivars Carina, Capella, Maxima, Mira, Rhea, Vela and eight advanced selections from the University of Adelaide almond breeding blocks are being trialled, plus Nonpareil as a control.

The team is including flexural rigidity measures of each tree while still in the nursery, to see if this measure could be used to identify varieties that would have relatively weak trunks prone to bending and producing a weeping or cascading growth habit, as with the variety Monterey.

New trials at Carina West Orchard, Victoria

The team has set up a demonstration site comparing Nonpareil and new self-fertile scion cultivars budded onto the Controller series of growth-controlling rootstocks, planted at high density. This trial site will evaluate the use of various growth-inhibiting plant growth regulators and possibly root pruning. The first commercial crop is expected in the 2019/20 season.

The project has a number of ongoing trials, including sites established at three farms in the Riverland region of South Australia and two farms in the Riverina region of New South Wales. The researchers report that data has now been collected from four consecutive seasons of these high-density trials, which are being managed using both standard and modified pruning systems.

The modified systems include the use of ‘selective limb-removal pruning’ (removing the shoulder branches of cropping trees) and reflective ground covers. Here the aim is to increase light interception and, by extension, yield in the lower areas of the tree, boosting overall tree yield. In earlier Hortlinks it was reported that while treatments increased kernel yield in the lower canopy zones, the crop produced in these zones was typically late to mature compared to the main crop at the tops of the trees, resulting in a need for additional harvests.

There is also the use of ‘small tree pruning’, including selectively removing strong branches growing out towards the centre of the rows, resulting in a ‘palmette’ style tree shape. Here the goal is to reduce shading and increase return bloom in the interior of the trees.

The researchers note that while yields continue to be satisfactory in the experiments, there is a definite need to address light interception – and for this, the best current strategy is to grow trees with a central leader structure, in order to produce a slender pyramid-shaped tree that is wider at the base than at the top, and consequently will not form a large shaded, barren zone in the centre of the tree. The first year’s flowering and yield data have been collected from trees planted in 2016 at high density and grown as minimally-pruned central leader trees. The first commercial crop is expected from these trees in 2019.

The project also involves trialling trunk girdling as a way to increase yield. While there has been no discernible effect recorded two years post-girdling on current trial trees, the researchers report that Nonpareil trees that were girded n 2014 in an earlier trial “are now significantly smaller than the non-girdled control trees, but they are producing similar yields”.

Finally, the number of trials is currently growing, with trees having been propagated for three new tree architecture/high-density trials to be planted during winter this year in the experimental orchard of the National Almond Centre of Excellence in Loxton, as well as another new high-density trial in a commercial orchard in Robinvale, Victoria. Further, new tree architecture/high-density trials were also planted in California in January this year, in collaboration with the Almond Board of California and university and nursery partners.

The project has a number of ongoing field trials involving pruning and light management studies. There are a number of areas of investigation, including but not limited to…

  • The use of ‘selective limb-removal pruning’ (removing the shoulder branches of cropping trees) and reflective ground covers. Here the aim is to increase light interception and, by extension, yield in the lower areas of the tree, boosting overall tree yield. So far, while treatments have increased kernel yield in the lower canopy zones, the crop produces in these zones have been late to mature compared to the main crop at the tops of the trees, resulting in a need for additional harvests. Work is ongoing in this area.
  • The use of ‘small tree pruning’, including selectively removing strong branches growing out towards the centre of the rows, resulting in a ‘palmette’ style tree shape.  Here the goal is to reduce shading and increase return bloom in the interior of the trees. If found to be a successful system of pruning, this would allow for closer row spacing in new plantings – increasing growers’ yields per hectare. The researchers report that a trial site established in 2012 continues to provide useful data on a pruning system that would allow 3m x 5m close row spacing, with data continuing to be collected during the 2017/18 season. A narrow palmette-style trial in a separate orchard is further evaluating the potential of this type of pruning system applied to young almond trees, with the first treatments applied in August 2017.
  • The use of trunk girdling to increase flowering, with the trees involved set to be monitored through the summer of 2018. Look for updates as they become available.
  • Studies into ‘central leader trees’ (with a single dominant trunk) and rootstocks. Here, four rootstocks and four almond cultivars are being trialled for suitability with central-leader training, with flowering and canopy development being monitored. The researchers note the first significant crop from this trial isn’t expected until the 2018/19 season.

During winter 2017, two new trials were planted on grower properties in the Riverina region, to evaluate the performance of trees grown as central leader trees for suitability in high-density plantings. There are also additional trials to be planted at the Almond Centre for Excellence.

Field trials in the project are ongoing. They involve pruning and light management studies.

Looking at the use of ‘selective limb-removal pruning’ (removing the shoulder branches of cropping trees) and reflective ground covers…

  • The goal is to increase light interception and, by extension, yield in the lower areas of the tree, boosting overall tree yield.

  • The researchers report selective limb-removal pruning has created more open, spreading canopies and, along with reflective ground covers, increased light interception and yield in the lower canopy zones of the trial’s mature, high-density-planted trees.

  • Based on the 2017 harvest, selectively pruned trees with reflective ground covers underneath produced twice as much crop in their lower canopies than untreated trees.

  • The crop produced in the lower canopy areas of the trees displayed delayed maturation compared to the crop in the upper canopy – indicating a need for additional harvests.

The project is also looking at ‘small tree’ pruning – including selectively removing strong branches growing out towards the centre of the rows, resulting in a ‘palmette’ style tree shape. The goal is to reduce shading and increase return bloom in the interior of the trees. If found to be a successful system of pruning, this would allow for closer row spacing in new plantings – increasing growers’ yields per hectare. The researchers report the narrow pruning approach applied to young trees appears sufficient to delay overcrowding of trees that are planted at high density, with work continuing.

Some of the other areas of investigation in the project include:

  • The use of trunk girdling to improve return bloom and promote earlier cropping on young trees

  • Evaluation of the performance of trees grown as ‘central leader trees’ with a single dominant trunk, for suitability in ultra-high-density planting systems.

The work originally began with the establishment of trial sites on two separate properties in Lindsay Point, Victoria, in 2014. This work has recently been expanded, with a new trial planted in the Riverina region, two new trials planted in the Riverland region, and a further planting set to take place near Hillston, New South Wales.

The Riverina and Riverland trials will be looking at new growing systems for new varieties. The objective of the work will be to quantify growth responses of new scion varieties to pruning regimes that are better suited to high-density planting systems.

Trial plans have also been agreed, and plant material ordered from nurseries, for new projects to be established in winter 2017. As the project progresses, new trial plots are set to look at optimised trunk girdling, high-density orchards optimised for new varieties and rootstocks, and more.

Related levy funds
Details

This project is a strategic levy investment in the Hort Innovation Almond Fund