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Getting to the ‘roots’ of soil health

Research & Extension

This article originally appeared in the Spring 2021 edition of AFG magazine, available online here.

Increasing attention is being given to soil health as the foundation of a healthy, productive orchard.

Dr Sally Bound is joint lead for the PIPS3 Program project Improved Australian apple and pear orchards soil health and plant nutrition project (AP19006), led by the Tasmanian Institute of Agriculture (TIA) and supported by Hort Innovation, using the apple and pear research and development levy. She believes this research will equip growers to better understand, measure and take steps to improve the health of their soil to maximise tree productivity and fruit quality.

“More and more evidence is showing the importance of soil biology,” Sally said. “The contribution soil biology makes is wide ranging – from recycling organic matter, making nutrients more available to plants to the hugely important role of supporting soil structure, so maximising the biology in your soil is paramount. It stands to reason that if you’ve got a ‘dead’ soil, your trees are not going to grow as well.”

Soil health is fundamental to environmentally sound and efficient production systems, and the findings from the research trials should assist growers in maintaining healthy soil biology that
promotes sustainability in fruit yield and land use.

One year in, this study is filling knowledge gaps in soil health best practice for orchardists, including regional variations, drawing on both established research trials across five regions (Tasmania, NSW, Victoria, South Australia and Western Australia) and observations from growing practices overseas.

“The issue is there’s no definition of what optimum ‘healthy soil’ is,” Sally said. “We know it’s related to physical, biological and chemical soil characteristics that influence factors such as
compaction, water holding capacity, nutrient cycling and biodiversity including microbe and invertebrate populations.

“There could be a lot to learn from other growers worldwide who have little chemical or fertiliser inputs, but rely on resilient, healthy soil with balanced nutrients. The project is providing a wider
understanding about what other countries are doing through a literature review.”

Covering new ground

Intensive research trials in Tasmania’s Huon Valley are taking place on a conventional established block of Jazz™ apples and a newly planted organic block of Morgana.

The PIPS3 Program orchard trial site is testing a range of cover crops with under-tree and inter-row plantings and mulches which will also be used to study the invertebrate population (both
pests and beneficials).

The inter-row plantings are trialling grass/clover mixes, a flowering meadow mix and a native flowering mix. The tree line cover includes a grass/clover mix, as well as compost/mulch, hemp straw and a more standard ‘mow and throw’ treatment.

“The research trials involve planting a range of species with different root characteristics – deep and shallow, fibrous, spreading and tap roots – to see if a mix of species can improve soil biology, and hopefully do so faster than the pasture species alone, such as clover, rye grass, fescue.

“Anything we plant also has to be pretty robust and resistant to orchard traffic, whether that’s feet or tractors.”

While the study aims to find the ‘ideal’ planting mix, according to Sally, any kind of ground cover is beneficial.

“In some regions growers often have difficulty getting good coverage in the inter-rows,” Sally said. “While the outcomes of the study will hopefully give us a much clearer picture of the most valuable combinations of cover crops in tree lines and interrows, growers can already try and move away from bare earth strips under the tree line. Even just letting the weeds grow can provide food for microbes.”

Building up benefits

Orchards that have already adopted these practices can provide some useful insight.

“When it comes to cover cropping, orchardists are worried about competition for water and nutrients – but orchards employing these practices aren’t really finding an issue with that, provided you don’t let what’s growing under the trees get too vigorous,” Sally said.

“We’ve also seen that these orchards are much more able to deal with drought conditions, as the organic matter in soil helps create a more sponge like structure. This can certainly be adapted to the varying conventional orchard systems we have across the industry without having to transition to a fully organic practice.”

But building up good soil health is a gradual process.

“It’s not fast,” Sally said. “You can start to see benefits within the first 12 months, but depending on the soil you start with, it can take two to three years minimum before you see significant results. If growers wanted to try to make their soil more ‘alive’, they can start by trying to reduce herbicide use and increase organic matter in soil – this includes not only plantings but also addition of compost or mulch or simply throwing the inter-row mowings onto the tree line.”

How do you test soil health?

There’s been plenty of laughs, and interest, generated by the wittily named Soil Your Undies challenge demonstrated at the Calthorpe orchard walk

The Soil Your Undies challenge was launched as part of the PIPS3 Program project in late August.

Growers in Tasmania and WA were introduced to it in the field with demonstrations at the APAL Future Orchards® Walks.

“What we’re looking for as part of the PIPS3 Program project is ways that growers can easily determine their level of soil health,” Sally said.

“Most of the growers who are keen to participate in the Soil Your Undies challenge are aware that they need to take some action. We’re hoping this becomes a good annual DIY check-up.”

What can growers do to check the state of their soils?

A spade is your best friend – dig a hole so you can see both topsoil and subsoil

  • Are old inactive roots decomposing (evidence of bacteria and fungi)?
  • Does the soil smell earthy (actinomycetes)?
  • Is the soil dark in colour (soil organic carbon)?
  • Is the soil well-structured (soil aggregation)?
  • Is there evidence of bioturbation (macrofauna – earthworms and beetles)?

Look for evidence of organisms

  • Count earthworms – 10–12 per spadeful indicates good soil health
  • Set pitfall traps for macro and mesofauna – we want to see a range of species
  • Examine nodules on legume (clover) roots – a bright pink/red colour indicates active nitrogen
    fixing bacteria
  • Rapid deterioration of wooden stakes is a good indicator of fungal activity (the cellulose in the wood provides a food source for fungi).

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