RESEARCH & EVENTS
Orchard resilience to short-term water stress
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SARDI Almond Production Research Team South Australian Research and Development Institute ( SARDI ), the research division of the Department of Primary Industries and Regions
THE threat of seasonal water shortages in the Murray Darling Basin is well understood . Less obvious is the occasional exposure of trees to short periods of drought due to faulty valves or pumps , blocked filters and power outages , particularly when coinciding with heatwaves . Short periods of water stress can impact the immediate health of an orchard and influence both the current and future years ’ crops . However , some rootstock and variety genotypes may be better equipped to tolerate these short periods of water stress . SARDI have started investigating the drought tolerance traits of almond rootstocks and varieties within its existing rootstock compatibility experiment located at the Almond Centre of Excellence experimental orchard ( Loxton SA ).
What did we do ? Early in season 2023 / 24 , irrigation infrastructure was overlaid across a high-density section of SARDI ’ s rootstock compatibility trial . The new irrigation valves enabled the application of two different irrigation treatments across each of 14 rootstocks grafted to 5 varieties . All rootstock x variety combinations were split into two sections , one section to remain fully irrigated and the other to be subjected to a short period of complete drought . In January 2024 , the irrigation was switched off for half of the trees , for a period of four days . Measures of canopy transpiration and stem water potential were collected before , during and after the period of stress and were complemented by soil moisture monitoring , canopy sensors and aerial imagery ( thermal , RGB and Multi-Spectral ). A subset of Nonpareil plots , grafted to six relevant rootstocks , were instrumented with additional
In A Nutshell - Autumn 2024 Vol 25 Issue 1
VARIETIES
( continuous logging ) sensors , including sap flow and under-tree timelapse imagery .
What did we measure ? Various measures of plant and soil water status were collected to complement the measure of canopy health , yield and nut quality metrics . Measurement techniques included :
● Granular matrix soil moisture sensors at depths of 20cm and 40cm below the dripline to monitor the availability of soil water .
● Stem water potential to describe the canopy ’ s water status , with tension increasing when water supply is limited .
● Leaf porometery to measure the rate of transpiration ( water loss ) directly at the leaf surface .
● Heat pulse sap flow sensors to give continuous monitoring of
ROOTSTOCKS Nonpareil Rootpac 20 Rootpac R Cornerstone Shasta Controller 6 Atlas Garnem Vela Rootpac 40 Controller 9.5 Felinem Almond 12 Controller 7 Nemaguard Monegro Almond 21 Krymsk 86 Barrier 1
Table 1 Varieties and rootstocks in water stress trial .
Continuous loggers reporting soil moisture , under canopy imagery and sap flow . transpiration ( rate of water use ) for the Nonpareil trees .
● Infrared canopy sensors ( continuous monitoring ) and aerial thermal imagery ( high spatial resolution ) to compare canopy temperatures and infer transpiration rates .
● Dendrometers to measure tiny changes in the diameter of tree trunks related to tree water status .
● Aerial multi-spectral imagery to assist with the calculation of vegetation cover and as an indication of canopy health .
● Canopy size and leaf density measurements to infer the longerterm effects of water stress on trees and adding context to rates and values of other measures .
What ’ s next ? SARDI are currently conducting harvest operations across all their field experiments at the ACE orchard . This includes assessing the impact of transient water stress on the yield and nut quality metrics of the 70 different rootstock x variety combinations in this experiment . Interpretation of soil , canopy and yield datasets will commence postharvest and be reported to industry as soon as possible . It is anticipated that drought treatments will be repeated in 2024 / 25 .
More information To visit this demonstration trial or any of SARDI ’ s other trials at the ACE experimental orchard , please contact SARDI on 08 8595 9100 or the ABA on 08 8584 7053 .