More than 20 growers across Queensland and New South Wales have joined on-farm trials to supplement core experimental sites investigating how to improve soil structure and lift crop yields in the northern region.

The trials, along with ongoing monitoring of long-term experimental sites, are part of the second phase of GRDC-invested soil amelioration research for dispersive soils, which are widespread throughout Queensland and NSW.

These soils typically become waterlogged when wet and very hard when dry, and they often have a poor ability to capture and store water. They are often sodic but can also be highly alkaline or highly saline.

The first five-year project – from 2018 to 2022 – established a range of treatments at Dulacca, Millmerran and Talwood in Queensland, and Spring Ridge, Armatree and Forbes in NSW.

Ongoing monitoring of crop results at these core experimental sites , with the addition of on-farm trials, is part of the new follow-on project, the $2.2 million ‘Economics of amelioration of soil sodicity’, expected to run until 2026.

University of New England (UNE) crop scientist Dr Richard Flavel was a key speaker at a recent webinar to share results from core site trials to date.

Dr Flavel said as much as 70 per cent of the country used for growing grain in the northern region has some kind of soil constraint that prevents crops from accessing water and nutrition at depth.

“This project, and the previous one, are seeking to figure out how we can re-engineer our soils so that we can get better capture of our water and our root systems can access that water over time. We can improve our water use efficiency in our system and ultimately our yields,” he said.

The research has been driven by the desire to increase yields during dry seasons (rather than improving drainage), when the gap between yield potential, based on soil moisture, and actual yield has been most evident.

One of the challenges is to assess the long-term benefit of interventions, Dr Flavel said. “We are continuing to assess these sites in the long term to work out how much benefit growers see from amending soil structure and what the best strategies are to make sure they stay fixed as best as possible."

Research site results

Results from core experimental sites over the past three seasons were shared at a recent soil constraints webinar, with presenters from UNE and the Queensland Department of Agriculture and Fisheries (DAF), who are partners in the project.

Soil amelioration treatments include combinations of shallow ripping (to 20 to 25 centimetres), deep ripping (40 to 45cm), fertiliser (at 20cm), surface and deep gypsum, deep organic matter,  and elemental sulfur.

Results across all core experimental sites indicated that deep ripping alone could provide a short-term increase in yield, but this quickly declined. In some instances, by the third year, yields at deep-ripped sites had dropped below those of the untreated control plots.

Fertiliser treatments typically provided the greatest improvements in yields, with some yields more than 20 per cent greater than those from the untreated control plots. But researchers acknowledged that the recent wet seasons across the north had confounded their results. Given the available moisture at most sites, crops were not struggling to access water and additional nutrients, masking the impact of soil constraints on crop yields.

However, the use of organic matter and elemental sulfur has provided some of the best sustained yield improvements three years after application, particularly at the NSW Armatree site.

At core sites in Queensland, composted feedlot manure was used for organic matter, while in NSW lucerne pellets were used, with both surface and deep-placed treatments. Elemental sulfur was placed with deep ripping, in combination with organic matter.

Dr Flavel explained that soil chemical processes converted the sulfur to sulfuric acid and in highly alkaline soils, this changes the pH and structure of the soil. It created calcium and made free lime available, which formed gypsum at the bottom of the soil profile.

Three years after the treatment was applied, the combination of organic matter and elemental sulfur produced the greatest yield and wheat protein improvements of all treatments at the NSW Amatree site.

“One tonne of elemental sulfur is equivalent to about five tonnes of gypsum. It’s experimental at the moment, but it’s showing some interesting results.”

Grower collaborations

Dr Flavel recognised that additives used at core experimental sites were well above commercially practical rates, with up to 10 tonnes per hectare of gypsum applied in some treatments, for example.

But the collaboration with growers in the current project will provide vital data on the effectiveness of more commercially practical and cost-effective options. On-farm yield improvements did not need to be “statistically significant” to make a difference to growers, he added.

So far, 22 grower sites are participating, from Forbes in central NSW to Tara in Queensland. Growers interested in taking part can contact Dr Flavel for more details.

“Using strip trials on-farm, we’re basically putting much more sensible rates down over much larger areas and we’re looking at the special effects and long-term impacts,” he said.

Growers already involved are trialling various treatments including combinations of deep ripping, fertiliser, gypsum, organic matter and lime, depending on their soils and farm systems.

Satellite and drone imagery is being used to track crop growth, and small cuts from crops ready to harvest are used to calculate yields in combination with grower yield monitor data.

Growers from central NSW through to southern Queensland can contact Dr Flavel to join the project, for more information or to register for the project’s biannual newsletter.

More information: Richard Flavel, richard.flavel@une.edu.au; Henry Baskerville, henry.baskerville@daf.qld.gov.au