Sundials have been used for over 3000 years to draw knowledge from light.

Invented to measure the time of a far distant past, the concept is being used anew by Agriculture Victoria researchers at the Goulburn Valley-based SmartFarm at Tatura to drive the design of orchards of the future that capture light more efficiently to yield more fruit of higher quality.

Led by Research Leader Dr Ian Goodwin, the team has established the world’s first multi directional experimental Sundial Orchard to analyse the relationships between light and fruit yield and quality.

While the design is millennia old, the research capability is state of the art. The experimental orchard is at the heart of a digitally enabled research and innovation facility with the technology to track and capture a breathtaking minutia of precise data, from fruit position to performance in storage, create virtual orchards to test different scenarios and provide growers with the tools to inform decision making.

In the process the team aims to build what it believes will be the largest, most precise dataset ever created for orchard fruit quality attributes, a dataset that will underpin development of a whole-farm model which can be used to analyse the economic benefits and risks of new orchard designs and mechanisation, their effects on yield and quality and allow net cash flow budgets over a 10-year horizon to assess the financial impact of management changes.

An aerial view of the Sundial Orchard at Tatura.

Let the light in

Sunlight is abundant in Australia but positioning orchard canopies to intercept as much of it as possible for colour and sugar development – but not so much it damages the fruit or drives excess water use – is still an imperfectly understood science.

By establishing clear relationships between light, yield and fruit quality, the Sundial Orchard research aims to fill that gap and enable the design of canopies capable of intercepting light more efficiently to increase both fruit yield and quality, and profitability.

“If we can build up our knowledge, we can then start thinking about how we might design canopies to get maximum fruit quality and minimise sun damage,” Ian said.

The orchard has been planted alongside the research facility’s existing pear, stone fruit and almond experimental orchards and the demonstration orchard of new apple and pear cultivars.

While orchards conventionally run row by row, the Sundial Orchard – designed to assess the impact of different orientations – throws its eight spokes or arms, each of five rows of trees, to the points of a compass. From the air its symmetry is strikingly pagan, a leafy experimental Stonehenge.

Four of the arms are planted to the Majestic Pearl nectarine to assess different training systems and the other four to the WA-developed ANABP01 apple cultivar marketed as Bravo™. Planted in 2018 at 1 m x 3.5 m spacing and trained as a slender spindle, the trees are currently at the end of their 2nd leaf.

The four spokes of apples (and of nectarine) are oriented:

• North East – South West
• North – South
• North West – South East
• East – West

The apple trees are grafted to three dwarfing rootstocks – M26, M9 and Bud 9 – randomised through each row to look at dwarfing and its interaction with canopy development in addition to the work on orientation.

An automated drip irrigation system irrigates the different rootstocks at different rates, allows for fertigation, and can send alerts of over- or under-watering to a mobile phone.

Don’t do this at home

Ian is quick to point out the layout is strictly for research purposes.

“Don’t anyone ever think that I am suggesting you grow an orchard like this,” Ian told growers, with a smile, at the APAL R&D Update in Melbourne in November. “It is an experimental orchard.”

When the orchard carries its first crop next year, research will focus on:

• risk of sun damage from different row orientations,
• colour response to exposure or shading of fruit,
• floral initiation,
• the effects of photo inhibition on photosynthesis, and
• water use efficiency.

“We are all well aware of the risk of sunburn in apple crops,” Ian said. “We have done some work in apples and pears on damage thresholds. What we are trying to look at in the Sundial Orchard is the impact of the natural shading from foliage in reducing the risk of sun damage associated with those orientations.

“We’ve also done work on shading fruit and colour development at various shade intensities. What we are interested in in the Sundial Orchard is what sort of effect the natural foliage cover is going to have.”

This year, with the fruit stripped to allow second year canopy development, the focus had been on measuring light and testing models of light interception.

“With those different row orientations, what we would expect is differences in how much light is intercepted by the trees, not only the total amount of light intercepted by the tree but how that light interception changes during the day,” Ian said.

“In a row that is orientated east-west we would expect that light interception would be pretty similar throughout the day as it is hitting the top of the tree as the sun goes through its arc, with very little hitting the sides. With a row orientation of north-south we find that in the morning it is hitting one side of the canopy, in the middle of the day there is much less total light interception as the sun is directly above and in the afternoon of course it is hitting the other side of the canopy.

“The other row orientations are a little more complex, but a model would show that a NW-SE orientation is going to intercept more radiation in the morning as the sun is striking one side of the canopy, some in the middle of the day and a lot less in the afternoon.

“A canopy will photosynthesise a lot more in the morning than in the afternoon whereas canopy transpiration is the opposite.

“If you design a canopy that intercepts more light in the morning than in the afternoon, it should be more efficient.

“The implications for NW-SE orientation are that in the morning if that radiation is hitting the side of the canopy that’s good conditions in terms of photosynthesis and colouring the fruit and it is also going to have water use that is reasonably high but not nearly as high as if you were intercepting a lot of radiation in the afternoon so an increase in water use efficiency.”

Ian said initial measurements of light interception were in line with what was expected from the modelling.

“That’s a really good start, so next year when we set a crop on this we’ll be able to do a lot more intensive measurements looking at that light interception over the day, its impact on colour development, impact on sun damage, on photosynthesis and on water use efficiency.”

Virtual orchard

Sensor technology has revolutionised data collection, but it is the ability to recreate 3D digital canopies with light detection and ranging (LiDAR) technology that promises to powerfully increase understanding of light interception.

Firing rapid pulses of laser light at an object, the LiDAR sensor records the amount of time the light takes to come back and builds up a detailed point cloud 3D digital orchard which can be used to model how light penetrates the canopy and how much reaches the ground.

The detail of the resultant digital image is striking, including not only leaves, and individual fruit positions, but flowers and potentially flower buds.

Ian said the ability to study the penetration of light through the canopy using a 3D digital LiDAR image in conjunction with light models was potentially very powerful.

“We are pretty excited,” Ian said.

“There are computer models, but they looked purely at interception based on an assumed geometrical canopy shape.

“What we have done in the past is to push a trolley up and down the rows to measure light and we could only measure total interception.

“To look at how the light goes through the tree and hits the fruit, we were doing spot measurements of light at each fruit and then relating it to the colour development and sunburn damage on that fruit. But it’s hard work being out there all day — you can stick a sensor there and even log the data , but it is not going to provide you with anywhere near the spatial and temporal detail and precision that LiDAR can provide.

“What we want to do is utilise those 3D digitised canopies to look at how the light is penetrating through the canopy.

“LiDAR really is a powerful research tool. Establishing relationships between light and floral initiation are feasible, observing the distribution of flowers in different tree training systems and rootstocks, and even measuring in situ fruit colour may be possible.”

A digital image of the pear orchard from a standard optical camera

The equivalent 3D digital image from the LiDAR instrument.

Opportunities

As well as providing opportunities to build better understanding of relationships between light and fruit quality parameters, Ian said the Sundial Orchard and the broader SmartFarm would open up new opportunities for collaboration with visiting scientists and other projects as well as demonstrating the opportunities within horticulture.

The site will be used to both evaluate sensors and sensing platforms, robotics and automation and demonstrate technologies available for use in orchards.

A newly established Technology Hub gives visitors an opportunity to see live data rolling in or some of the agtech tools in action and their potential for use in the orchard.

“It’s an education facility, not just for growers, but for students,” Ian said. “The idea is to encourage students to have a career not just in science but in horticulture.”

Further information

The Sundial Orchard and Technology Hub are not open for visitors at the moment due to COVID-19 restrictions, but when movement restrictions are lifted, visits can be arranged by contacting Michael Halverson on 0447 958 977.

The Sundial Orchard and Tatura SmartFarm are Agriculture Victoria initiatives funded by the Victorian Government.