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Experimenting with bio-stimulants in Australia's Rangelands.

Supporting soil health

If soil biology is key for farming resilience, how can we improve soil biology? 

At the beginning of 2022, four NSW rangeland producers and NSW Department of Primary Industries (DPI) soil scientists discussed this question at a workshop. The workshop focused on co-designing trials that would test various management practices for restoring the Rangelands. 

Inspired in part by one of the core producers who had experimented with Johnson Su compost,

all four of the producers were keen to test other bio-stimulants as part of the Rangelends Living Skin project, funded by the Meat and Livestock Association. 

Andrew and Megan Mosely, one of the four core producers, explained, “We are really keen to improve our rangelands and to try different things. These bio-stimulant trials are a good way to test these ideas on our farm and improve our understanding of some of the factors at play in soil health. Plus find cheap and effective ways to improve our landscape.”

Rhizosheaths, forming around plant root systems, are stimulated by functioning microbial communities in healthy soils (Photo credit: Lee Fielddhouse).

What are bio-stimulants?

Several terms are used to describe products and practices that stimulate soil biology, such as bio-stimulants, bio-primers and bio-amendments. Essentially these terms describe organic liquids and solids that enliven the soil’s microbial community, or ‘below ground herd’. 

According to Dr. Neil Wilson an Australian microbial ecologist:

  •  Direct bio-stimulants are living microbes, preferably grown on the farm, such as with Johnson Su compost.
  •  Indirect bio-stimulants are organic materials that provide essential services to the soil microbial herd, such as nutrients and organic carbon (shelter).

Lee Fieldhouse, a producer of the worm compost liquid bio-stimulants used in the trial, has observed how bio-stimulants support and entice microbial communities to come together. For example, rhizosheaths formed by microbial communities help roots grow faster and deeper, thus enabling the plants to access more water and nutrients. According to Lee, “There are no downsides to getting your soil microbiology humming.” 

What impacts of bio-stimulants will the project team look for?

Soil science has expanded from chemistry to recognising the role of the soil microbial community in producing 15 of the 18 naturally occurring chemical elements essential to plants. 

Similarly, the producers in the Rangeland Living Skin project agree that soils contain highly diverse and beneficial microbes, but wonder if the previous land management practices have caused these microbes to go into, what Dr. Neil Wilson calls a dormant or ‘starvation’ state. 

Glenn and Julie Humbert, also core producers in the project, said, “We’ve either got a soil that is increasing in its biological activity, because our management is allowing that to happen, or it is going to the other way, and the water, mineral and biodiversity cycles are falling apart, which would mean all of our nutrients are eroding away.” 

As part of the Rangeland Living Skin project, four producers wanted to test how bio-stimulants can promote the growth and activity of soil microbes in order to stimulate beneficial ecosystem services. 

Specifically, in undertaking these replicated trials across properties near Wentworth, Brewarrina, Bourke and Cobar, these NSW producers wanted to observe how bio-stimulants might improve:

  • pasture biomass (and thus grazing feed volumes)
  • plant health and diversity (and thus animal health and carbon sequestration)
  • soil microbial community volume and diversity (and thus soil mineral cycling)
  • soil aeration, water infiltration (and thus pasture resilience).

As Lee Fieldhouse said, “If you are able to harness these natural soil functions for very low cost or even free, producers save money and are better off during both drier and wetter periods.”

Bio-stimulants in the replicated trials

Based on the co-design process, the Rangelands Living Skin team, including producers and soil scientists, designed a trial that could be replicated across four farms in the NSW Rangelands. All four producers are testing foliar sprays and solid worm castings, and two producers are trialing biochar. 

NSW DPI research lead, Dr. Simon Clarendon explains the benefit of the replicated trials as offering an opportunity for producers to trial treatments on a small scale prior to large scale applications on their properties. For example, Andrew and Megan Mosely wanted to include biochar in the replicated trials as they have an issue with woody shrubs now dominating parts of their pastures, reducing the ability of native grasses to stabilise the soil and provide nutrition for their stock. 

In the future the Mosely’s hope to create biochar from these home grown materials, but want to know the influence of this bio-stimulant before expanding to a larger scale production. Andrew said, “With 20,000 hectares, we can’t afford to use fertilisers. We want to use what is available on our farm to create bio-stimulants to help cover a huge area.”

Dr. Simon Claredon believes the opportunity to investigate soil and plant benefits of various treatments on a manageable scale in a scientifically rigorous manner is an important benefit of the trial. He clarified, this experiment “was not intended to test specific products, but rather seeks to compare the influence of different treatments of interest to the producer to ‘control’ plots that do not receive a treatment.”


For the trial, project team members selected ‘randomised plots’ (with three replicates per plot), all 100 square meters in size, to apply:

  • a liquid vermicast as a foliar spray (Biocast) at 5 litres per hectare
  • solid vermicast, or worm castings (also sourced from Island Biologicals) at 250 kg/per hectare
  • biochar (sourced from Tamworth) at 10 T/per hectare
  • a control site with no amendments.

The process of the replicated trial

In May, the visiting DPI team and producers selected trial locations of largely perennial native grasses under rotational grazing management that could benefit from increased biomass. The trial locations were as uniform as practically possible, and ideally near the residence so as to be easier for the producers to observe over time. 

To begin, NSW DPI undertook initial chemical composition and soil food web soil samples of the trial sites as a baseline before treatment, and in July, the team returned to apply the biostimulants.

The foliar was applied using a 15L spray backpack late in the evening, or early morning to aid absorption into the plants and soil (before the heat of the day), and the biochar and vermicast solids were applied by hand. 

The biochar was applied using two different methods, depending on the soil scientist’s recommendations:

  •  One producer disturbed his soil to increase water infiltration, so he applied fine particle biochar, with the hypothesis being that the finer particles aid soil biology more quickly.
  • The other producer did not want to disturb his soil, so he applied larger biochar particles to prevent it from blowing away.

Observing differences between treatment and control sites

Since the trial began, the four participating producers have been keeping an eye on their trial sites. Anecdotally, one has observed that the biochar site has grown more clover. 

In addition to producers’ observations, the NSW DPI team will use several quantitative methods to assess potential influences of the bio-stimulants. By comparing soil tests taken in May and December, the team will look for any changes in soil chemistry (such as carbon and nitrogen) and biology (such as the bacteria to fungi ratio), compared to the control sites.

Popularised by the Soil Your Undies movement across Australia, another very affordable and accessible test for understanding the presence of the microbial community in the soil is the cotton strip test. The test is based on a simple premise: the greater the microbial community, the faster the cotton strips disappear over time. 

To compare activity of below-ground microbial community over time across the trial sites, the team buried three 5cm x 5cm cotton strips in each trial site. Producers removed one cotton strip, ‘very carefully’ according to Glenn and Julie Humbert, at eight weeks, 12 weeks and 14 weeks after applying the bio-stimulants at each site. Where cotton strips are still intact, NSW DPI will aso use a tensometer to measure the breaking point of the remaining cotton. NSW DPI will also use an app that measures greenness (Canopeo) by placing the degraded strip on a green background to calculate the percentage of material left.

While the final cotton strips are yet to be assessed, Project Manager Sarah McDonald was surprised by the amount of decomposition of the cotton. She said, “At the end of the 14 weeks we weren’t able to see any cotton at some of the sites, and that was faster than we expected.” Similarly, Andrew was surprised at how quickly the cotton strips degraded, as well as the varying levels of degradation amongst the cotton strips.

Challenges along the away

Any paddock trials will have challenges. One producer’s flags marking the location of his cotton strips blew away. Several of the producers have had to graze the paddocks before biomass studies could be undertaken. But much like producers must do every day, the Rangeland Living Skin team is rolling with these circumstances. 

One of the most significant impacts of the trial is the above average rainfall, the incredibly wet season and navigating flooding conditions in some areas

This has been a challenging time for many. 

With the wet conditions spurring significant plant growth, the team is wondering if there will be an observable impact of the biostimulants in the short-term. As Dr. Simon Clarendon, research lead, said, “The rain is such a big lever that sits above the impact of everything else in the last four months, it may be hard to distinguish between all the variables.”

Learnings of the trial

While the results will be analysed early next year, one of the biggest lessons for the team so far is that little is known about the soil biology in the Western Rangelands, and the whole team is looking forward to learning more about the soil biology more generally, through these trials. 

Despite the challenges in undertaking the trials in a wet year, the Rangeland Living Skin team is excited to see how these trials might indicate which practices could be appropriately

applied across much larger tracts of the Rangelands, a vital ecosystem vulnerable to increasingly extreme weather conditions. 

We are trying to have a positive influence and have seen some pretty encouraging results so far. There is a lot we don’t know, but we’ll keep trying to work with nature, and projects like this help a lot in helping us to improve the landscape,” said Andrew Mosely.

Keep in touch

For updates on the trial visit the Rangeland Living Skin webpage to sign up for the newsletter or upcoming webinars.

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