RESEARCH & EVENTS broader root distribution, while drip systems concentrated roots near the emitters. SARDI’ s DNA-based root quantification assay will again be used through season 2025 / 26 to assess root density and distribution, helping to link root traits with yield, canopy development and water use efficiency.
Figure 2. ACE soil sampling at SARDI’ s Soil Amendment experiment in 2025 / 26( 8 th leaf)
From page 39 The large scale and design of the trial, spanning 7ha and incorporating four varieties across 12 soil amendment treatments, has preserved its experimental integrity despite early tree losses caused by strong winds. While some treatments now have fewer replicates, the trial continues to support meaningful comparisons. Now approaching its eighth leaf, the experiment is generating valuable insights into how different soil management strategies affect soil condition, root development and overall crop performance.
Compost: Promising at higher rates To date, compost treatments at 10t / ha, whether applied to the surface or subsurface, have shown minimal yield advantage over plots with no compost. In contrast, higher-rate applications, such as 50t / ha at planting or annual applications of 10t / ha, are trending toward cumulative yields approximately 10 % higher than the controls by the seventh leaf. These trends will be more thoroughly analysed when the 2026 harvest data is incorporated into the final report, scheduled for release in December 2026. Soil testing in the orchard’ s third leaf revealed that compost improved physical properties such as bulk density and water infiltration. Chemically, it boosted organic carbon, phosphorus, potassium and cation exchange capacity, especially at the higher application rate of 50t / ha. Despite these gains, early measures of readily available water showed no significant change, likely due to the coarse texture of the compost. A reassessment of these metrics is currently underway, five years after the initial evaluation.
Supersoil: Strong Start, Weak Finish One of the more novel treatments tested was the Supersoil mound, created by growing ryegrass in the midrow and incorporating it into a tree-row mound before planting. This approach initially improved soil fertility, microbial activity and root density. Supersoil plots had the lowest soil strength and highest microbial activity, inferred by a Tea Bag Decomposition Index and DNA assay of the soils biological profile. Root DNA analysis also confirmed deeper and denser root systems in these soils. However, these benefits didn’ t translate into practical success. Supersoil plots suffered from weed pressure, tree blow-outs and harvesting inefficiencies due to steep mounding. The long lead time between amendment and planting( at least one season) also made this method commercially less viable.
Root Systems and Irrigation Sprinkler irrigation encouraged
Looking Ahead Soil analysis is currently being repeated to evaluate the longerterm effects( eighth leaf) of the soil amendment treatments. While further assessment is needed to confirm the yield benefits of compost applications, early findings suggest that elevated soil carbon levels persist even five years after application. This sustained carbon presence may have positive implications for carbon sequestration and supports the potential use of almond hulls and shells as effective organic amendments.
Final Thoughts Although compost and Supersoil treatments enhanced soil health and root development, these improvements did not always translate into higher yields. The SARDI team is currently working to better characterise the benefits of organic soil amendments as it approaches the final reporting period for this and other ACE-based experiments( due in December 2026). Findings from this trial may be particularly relevant for systems aiming to reduce synthetic inputs or close the loop on agricultural waste. For now, trial results reinforce the notion that building soil health is a long-term commitment.
More Information If you are interested in discussing or visiting any of SARDI’ s field experiments, please contact Nigel Fleming( 0401 122 136) or Tim Pitt( 08 8303 9400).
Acknowledgement SARDI’ s AL21001 project is funded through Hort Innovation’ s Almond R & D levy fund and contributions from the Australian Government, with coinvestment from the South Australian Government. Further information from www. horticulture. com. au
40 In A Nutshell- Spring 2025 Vol 26 Issue 3