Ensuring future cropping viability: The bottom line of soil amelioration

With more than 7.8 million hectares of soil considered sodic and producing yield gaps across NSW and Queensland, the soil constraints project investigates the impact of different amelioration strategies on soil water storage and grain yield.

Established in September 2019 by the University of New England and the Department of Agriculture and Fisheries Queensland, the GRDC-funded project includes six core experiment sites and more than 20 commercially focused grower sites.

The NSW core sites are at Forbes, Armatree and Spring Ridge, while those north of the Queensland border include Talwood, Millmerran and Dulacca.

Wheat, barley, canola and lupins have been trialled in NSW.

The research aims to eliminate sodic soil constraints in the upper 50 centimetres of the soil profile using physical and chemical ameliorants, including tillage, banded nutrients, gypsum, organic amendments, and elemental sulfur.

While ameliorating subsoil constraints can be challenging and costly, some treatments have already demonstrated yield increases of 30 to 40 per cent.

However, Richard Flavel, a University of New England associate professor of crop science, said it isn't a one-size-fits-all approach.

"With 14 treatments, including one control, there are so many different treatments and combinations that were largely selected based on soil tests," he said.

"It does depend on what type of soil you're working with as to what is likely to help.

"It also varies seasonally because, in the wet years, we got certain types of responses, often around the nutrition angle, and in the dry years, it became more about how we're changing water availability."

Treatment responses have been highly dependent on the location, crop, season and longevity.

At Armatree, gypsum amendments, organic matter, and elemental sulfur increased water use efficiency. The site also responded well to physical disturbance.

Deep ripping was highly responsive in Forbes, however, the benefit of deep rip control has declined over time. Where ripping was combined with amendments, longer-lasting benefits were observed. Gypsum, elemental sulfur, and organic matter treatments all improved yields.

Spring Ridge was generally not responsive with only some minor effects of ripping and elemental sulfur.

"The GRDC has had two investments in this project, and at the end of the first investment, we did the maths and thought some treatments were never going to pay themselves back," Mr Flavel said.

"We were expecting very large numbers, so when we revisited it, we were surprised it was paying itself back much faster than we thought.

"Some of the treatments were paying themselves back in one year, so you're out in front within one season.

"Most of the time, those treatments were cheap and possibly didn't have huge gains, but they paid themselves back because they were so cheap.

"On the other end of the spectrum, we have some treatments that we never thought would pay themselves back, but they have made a massive impact to yield over time."

Following three wet and one dry seasons at Armatree, return against deep ripping treatments with amendment saw an income increase of $1000 to $2000/ha.

Based on a four-year average, payback periods for ripping with gypsum ranged between two and six years, with benefits appearing particularly in dry seasons.

Across three crops at Forbes, ripping treatments against the control returned between $2200 to $3300/ha.

For those treatments, payback periods were less than one year for nutrition, increasing to almost two years for higher input rates.

Lower benefits were noted in Spring Ridge across four crops as deep ripping returned between $300 to $400/ha

University of New England associate professor in soil fertility Chris Guppy said growers should view the data with a long-term perspective.

"While deep ripping on its own pays itself back almost instantaneously, and it has yield responses in the first two years, in the long term, we're of the opinion that farmers should be avoiding just ripping," he said.

The research indicates that deep-ripping compacted soils provide short-term benefits; however, the soil often collapses soon afterwards and sometimes deteriorates to a worse condition than before.

Mr Flavel said that economically, it can look really attractive, but sustainably, and in the long term, it could be quite destructive.

"From a scientific perspective, there is a lot of interest in the organic matter and the elemental sulfur treatments because they are changing the soil and making it much more productive," Mr Flavel said.

"They are very interesting because they are increasing yields by a phenomenal amount, 30pc to 40pc, which is pretty cool, but they also come with a big price tag.

"We still have some more work to do on making that a practical thing for farmers to take up.

"In terms of solving a problem for farmers, at the moment, I don't think we're quite at the stage to say this is the answer, and this is how you do it."

However, Mr Flavel said some gypsum treatments have had an effect and are quick to pay themselves back.

"The yield benefits are more modest but so is the price tag, so in dry conditions which is both when we don't necessarily have as much cash flow and the best time to be putting in these treatments, they are a lot more achievable," he said.

Mr Guppy said this research was critical to the viability of grain-growing regions west of the divide.

"Farming in those regions is only going to be sustained if we find ways to improve root access and efficiency of using the water that does fall and storing it in such a way that the plants can then access it later," he said.

"If we don't do the research now to work out whether it is even possible to increase the efficiency with which we use the decreasing and more sporadic rainfall, then there are communities that won't be viable going forward."

Mr Flavel said it was one of the tools growers could potentially use to iron out the bumps that climate change has created.

"There are a lot of avenues that we're looking at to try and make things happen, but this is one of the ways that we can get a fairly significant step change in productivity out of the system as it currently stands."

The soil constraints project will continue until June 30, 2026.