Identifying factors that influence spur productivity in almond (AL14005)
What’s it all about?
Established in 2015, this project is being conducted as part of a coordinated research program into boosting almond productivity and profitability.
Because spurs bear the vast majority of nuts on almond varieties used in Australia, spur population dynamics are of interest in understanding yield fluctuations and trying to maintain high yields from season to season. To this end, this project is investigating the behaviour of fruiting spurs of Nonpareil and Carmel almond cultivars under different management conditions, with the goal of developing better ways to manage orchards.
During the 2017/18 season the researchers investigated the factors that determine fruit number and kernel yield in a season, focusing on the effect of altered water and nitrogen supply on the physiology and yield formation of spurs across Carmel and Nonpareil trees.
Nitrogen fertiliser supply was reduced by 44 per cent and the irrigation volume was reduced by almost one third (30 per cent). The irrigation volumes were still high enough to sustain the water requirements of the trees, but reducing the water and nitrogen supply reduced the canopy density compared to the control experiment (with no changes to nitrogen or irrigation), so that less light was intercepted by these canopies.
Nitrogen and irrigation reductions increased yield
Overall, less dense canopies produced more nuts. However lower limb dieback, commonly observed in Nonpareil trees, further reduced the canopy density in the lower half of the trees, presumably with fewer spurs, and subsequently a lower number of nuts were produced per Nonpareil tree in comparison to Carmel trees.
The effect of nitrogen supply on kernel size was greater than the effect of irrigation volume. On the other hand, the irrigation volume had a greater effect on the kernel yield per hectare.
In Nonpareil trees, spur mortality rate increased as the number of nuts per spur increased. This effect was curtailed as leaf area per spur expanded. Spur survival was, however, reduced to zero per cent when only nuts were borne on a spur. In contrast, the Carmel spur mortality rate did not depend on the extent of leaf area for vegetative spurs. The mortality rate of nut bearing spurs was lower than seen in Nonpareil nut bearing spurs.
Consumer taste testing
Kernels from the harvest were tasted by around 300 consumers to see if the nuts from the Nonpareil trees in the trial were perceived as different from those from controls. Around a third of the tasters could detect differences, showing that irrigation and fertiliser supply treatments changed the properties of kernels somewhat, but the initial testing didn’t provide an indication what the basis of distinction might be, or whether there was preference for one lot of kernels over another. Further work is to come.
Research is being conducted on a mature commercial almond orchard at Lindsay Point, where the team is looking at the effects of differing water and nitrogen supply regimens on spur survival and fruiting, as well as leaf area per spur. Both nitrogen and water supply strongly influence spur leaf area and leaf function (photosynthesis), and these in turn are strong indicators of whether a spur will survive from season to season, and whether it will bear a fruit.
The fate of individual spurs in the trial trees is being tracked over the project’s five growing seasons, with the third season of trials now completed. At the time of writing, harvesting had been completed and data analysis was underway.
The researchers note that continuity of treatment applications and observations is critical, as spurs may live for several seasons, though they rarely bear fruit in two consecutive seasons. For this reason, project results will only be known over a number of seasons.
As well as observations about spur response to the treatments, the researchers are looking at other environmental and management factors including tree architecture and the light environment.
Look for updates as project observations are consolidated.
Produced earlier in the project, the below posters remain available for growers, summarising preliminary findings from the research…
- Rootstock/fertiliser management systems for almonds (explaining the project’s research into the effect of variations in the ability of rootstocks to take up nitrogen)
- Spur survival: Difference between cultivars (the project’s first-year spur-survival data)
- Spurs: Driving productivity (showing the project’s non-destructive method used to estimate spur leaf area)
In case you missed it, project leader Michael Treeby also presented information on the research at the 2017 Australian Almond R&D Forum & Field Day, held in October. Access the video and presentation material here.
Nitrogen and water supply strongly influence spur leaf area and leaf function (photosynthesis), and these in turn are strong indicators of whether a spur will survive from season to season, and whether it will bear a fruit.
Nitrogen and irrigation supply treatments designed to alter shoot growth and spur behaviour have been applied for two consecutive seasons in the project’s trials. The researchers will be continuing to track the fate of individual spurs in the trial trees over multiple years, and under a variety of management conditions, to describe the factors that influence a spur’s longevity, and to develop better ways to manage orchards. They note that continuity of treatment application is critical as spurs may live for several seasons, though they rarely bear fruit in two consecutive seasons.
So far, reducing water supply to 70 per cent of crop evapotranspiration (Etc) has decreased stem water potential (the ‘gold standard’ for assessing tree water status) in both Nonpareil and Carmel varieties on all measurement dates over the two seasons – though the effect was greater on some days than others. The effect of restricted water supply on Nonpareil tree water status was largely uninfluenced by nitrogen supply, but although the water status of Carmel trees was affected by nitrogen supply, clear trends were difficult to discern.
The survival and fruiting of a large number of spurs across the trees in the various treatments is currently being assessed, as is the leaf area per spur.
The project is tracking the fate of individual spurs in trial trees over multiple years and under a variety of management conditions, to describe the factors that influence a spur’s longevity, and to develop better ways to manage orchards. The collection and analysis of data continues, with Nonpareil trees in the study harvested in late February this year, and Carmel trees harvested in late March.
Data collection and analysis continues. Between April and August 2016, the number of spurs, the weight of kernels and the weight per kernel produced by trees in the study were collected.
Chemical analysis of leaves was also conducted to determine the effect of a reduced-nitrogen application treatment on trial trees. Results from both 2015 and 2016 show this treatment decreased the amount of nitrate nitrogen and total nitrogen in the leaves, while increasing amounts of magnesium and potassium.
Machine-hulled and shelled kernels from one of the cultivars in the study, Nonpareil, were also assessed for visible carob moth damage. The reduced nitrogen did not appear to have an effect on visible damage, but kernels that had received reduced water had higher amounts of damage.
Information from this project has been presented as part of field days and on social media.
In recent years the industry has experienced strong yield fluctuations between seasons and lower than average yields than would have been expected from historical observations. This is of concern to the industry given that the reasons for such yield fluctuations are not well understood. This highlights a need to recognise the underlying environmental and management factors that contribute to seasonal yield variations, including the physiological determinants of fruit bud initiation, fruit set and fruit retention, which are major contributors to yield. This project aims to provide better understanding of the physiological factors that determine number of fruit and kernel yield from season to season.
Data collection to date has clarified a number of methods; specifically, the way non‐destructive spur leaf area can be measured and the measurements required to accurately describe the light environment in different canopy zones. These go towards achieving the objectives of the project, namely to quantify spur growth and development of Nonpareil and Carmel within and between seasons, and to develop an understanding of the interactive effects of key management factors (irrigation and nitrogen), and the light environment on spur dynamics.
This project is a strategic levy investment in the Hort Innovation Almond Fund