South West

Improving Soil Health To Reduce Fruit Tree Mortality

This trial is now complete

Key Messages

  • Soil health was assessed by comparing orchard soils to soils under reasonably well managed permanent pasture with the same soil type and climate. Indicators of soil health included soil organic carbon, labile carbon, pest and beneficial nematode numbers, mycorrhizal fungi and soil respiration to indicate microbial activity. The analysis suggested that orchard soil health was poor.
  • Tree health has improved during the trial, but the effect was not caused by the soil products trialled. The grower has changed the time of pruning and use of chemicals and fertilisers, all of which may have had an effect on soil and tree health.
  • Soil health in inter-rows appears better than in tree-rows. It is recommended that trials are established to see whether soil health in the tree rows can be improved by under-tree mulching, throwing inter-row mow beneath trees or allowing pasture species to grow under trees.
  • The project has convinced the grower of the importance of using multiple tactics to improve soil health. David is now interested in building soil carbon in tree rows by making compost on farm from orchard waste and spreading it beneath trees.
  • Trial Rationale
  • Steps Taken
  • Lessons Learnt
  • Looking Forward

Trial Rationale

David Giumelli manages 25 hectares of orchard in Balingup for Casotti Enterprises, where he produces apples, plums, nectarines, peaches and apricots. He has traditionally managed the orchard “by the book”. But when trees started dying, David started to think more about the effectiveness of his whole programme.


“The way we deal with these problems is a real issue for me,” David said. “Everything seems to evolve around chemical control and less so around biological control. We are using more and more chemicals. The cost is one thing, but the damage is another.”


The cause of these deaths was not clear. The main signs of poor health in the apricots, which were planted in 2011 on sloping, well drained land, was bacterial canker and shot-hole.


Rather than just looking for short-term solutions to on-going problems, David wanted to build a more resilient system. So, working on the theory that poor tree health is linked to poor soil health, David has begun a journey to develop a system that improves soil health and resistance to disease.

Steps Taken

The key to disease resistance is a strong and diverse community of soil organisms. Concerned with the impact of chemicals on these soil organisms, David started to cut down on winter copper fungicide sprays in 2015.


“Chemicals are vital to reduce our fear of crop failure, and I would have a lot to answer for if an outbreak occurred.” David said. “But a lot of stuff goes out that doesn’t need to. So, if the weather hasn’t been good for spores to form and the numbers are down, I’m not going to spray just for the sake of it. We normally put insecticides out in winter too, but we are trying to improve timing and precision by monitoring for insects first. So I’m just trying to draw back where I can.”


Also, in 2015, David changed the timing of apricot pruning from winter to post-harvest when green leaves are still on the trees. This aligns with recommendations to avoid pruning when cankers are active in winter (Hetherington 2005).


In November 2015, David met with consultants from two separate agribusinesses who suggested he trial products that they sell to improve soil health. At the same time, David met representatives from South West Catchments Council (SWCC) who agreed to help him trial the products. A third agribusiness later became involved in the trial.


For many growers looking to improve soil health, deciding whether to use soil conditioners, stimulants or inoculants (hereafter called “soil products”) is often perplexing. It is often argued that the rates of these inputs are too low to have an effect, the microbes are already present in the soil, or that solutions need to be more holistic with all aspects of management considered. To provide evidence either way growers need to trial products to see if they work on their farm, using appropriate trial designs that can measure whether there has been a response.


During the course of the project, SWCC engaged Dr Graham Stirling, lead author of “Soil Health, Soil Biology, Soilborne Diseases and Sustainable Agriculture.” Dr Stirling has been involved in the development of integrated pest management alternatives to the soil fumigants and nematicides used in some horticultural industries. He has an interest in soil health and has assessed the value of using free-living nematodes as an indicator of the biological status of soils. SWCC engaged Dr Stirling to assess the biological status of the apricot soils by comparing it to a nearby permanent pasture and to other orchards.


During a visit to David’s property, Dr Stirling noticed that tree roots growing in the inter-row appeared healthier than in the tree row. This raised the possibility that the biological status of the inter-row was better than the tree row.


The aims of the project were to:

  1. Assess whether selected soil products were able to improve tree health compared to a control treatment (David’s standard practice) (2016-18),
  2. Assess the biological status of soils in the apricot orchard (2017), and
  3. Compare the biological status of soils in tree rows and inter-rows (2017).


Detailed methodology is available at )

Lessons Learnt

David’s orchard soils are in poor biological health compared to a nearby permanent pasture on similar soils and slopes. His apricot soils tend to have high numbers of ring nematodes that will be damaging roots, thus restricting water and nutrient uptake, a concern on upper slopes where soils are shallow. It is not known if ring nematodes also promote disease in apricot roots. Mycorrhizae in the upper slope apricots is also lower than pasture soils.


David’s apple soils also appear to be in poor health with high numbers of root lesion nematodes and low soil carbon compared to attainable levels.


However, based on tree health monitoring of 80 trees conducted in the trial, apricot tree health in an area impacted by disease seems to be improving. David has changed many practices over the past three years. It was not possible to attribute this apparent improvement to one particular cause.


There was no evidence that soil products caused a response in tree health, because tree health in the control improved at the same rate as the treatments. This doesn’t mean they don’t work, only that they appear not to have worked in this case. Dr Graham Stirling, suggests that to improve health of orchard soils, a range of tactics will be required. These may include increased mulching around trees or experimenting with cover crops in the row to increase soil carbon, reducing compaction in the inter-row, applying nutrients more frequently but at lower rates and minimising pesticides to reduce impacts on beneficial soil organisms (Stirling et al 2016).


David agrees that improving soil health requires a more holistic approach. He started using some of these tactics before starting the trial and is continuing to expand this approach. However, he still believes inoculants have a place as a one-off application when re-planting orchards and has adopted other products such as fulvic acid over his whole orchard.


“One thing I got out of the trial is that using any of these products won’t give you a greater result if your management doesn’t work with these products,” David said. “The way you do things and what you do is more important than one or two products to get a result. You can’t expect a result by adding biology when management works against it.”


A comparison between tree-rows and inter-rows in three orchards suggests that the inter-row is in better health, with up to 1% more soil carbon, typically less pest nematodes and more mycorrhizae. Dr Stirling recommends trials to see whether soil health in the tree rows can be improved by under-tree mulching or allowing pasture species to grow under the trees.


The project has helped to demonstrate a useful method for assessing soil health by comparing it with a nearby well-managed permanent pasture in the same soil type and climate. This comparison allows growers to understand what their attainable soil carbon levels are and provides a long-term target for soil carbon. Healthier soils are typically those that have carbon levels close to attainable levels for that soil type and environment.


Using soil carbon is the simplest measure to use in comparing trial sites to well managed pasture because it is included in standard soil tests. More sophisticated methods such as mycorrhizae spore counts, CO2 respiration, and pest nematode counts also appear useful, especially to see short-term responses, but correlations can be weak.

Looking Forward

The project has convinced the grower of the importance of using multiple tactics to improve soil health. David is now interested in building soil carbon in tree rows by making compost on farm from orchard waste and spreading it beneath trees. He will also look at mulching inter-rows and throwing the mow beneath trees, and possibly creating a more species-diverse inter-row. For him, the story has just begun.


Project Snapshot

Land Manager
David Giumelli
NRM Region:
South West
Property Size
100 ha
Average Rainfall:
Very High - More than 750mm
Enterprise Mix:
Perennial Horticulture
System Constraints:
Fruit tree mortality, Soil Biology
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