Lime spreading project reveals need for input upkeep

The Regenerative Agriculture Program, delivered by the Eyre Peninsula Landscape Board and facilitated by Agriculture Innovation and Research Eyre Peninsula was funded through the Australia Government's National Landcare Program.

The program delved into sustainable agriculture practices across 55 sites to provide insights into how different EP soils respond to lime treatments as well as what happens when it is left.

Sustainable agriculture project officer Josh Telfer said the widespread project highlighted a "re-liming story".

"A lot of farmers are already spreading and testing lime, the nuance is the re-liming story. Once paddocks have been limed once, it is important to understand it is not the end of the story," he said.

"Lime needs to be monitored carefully to work out how much and how often re-liming is needed to keep the soils on the correct trajectory."

Increased farmer awareness about lime spreading and its economic viability came about through a few factors, according to Mr Telfer.

"It has been the perfect storm really," he said.

"There are providers looking at variable rate Ph maps to provide farmers with more information, new lime pits opening on the EP, so the transport component is less and rising land prices.

"Farmers are trying to make the land produce better and dealing with soil acidity is important for improved production."

A project outcome for farmers with soil acidity issues was an overwhelming indicator to test the soil pH in the surface and subsurface with a field kit and also at a lab.

Soil was sampled at 5 centimetres and 10cm intervals and showed once liming had begun, farmers needed to sample at 5cm increments.

"Farmers might think the lime is working but it is just stuck in the top 5cm," Mr Telfer said.

"The soil work has also showed when lime is spread, it does not react instantly with soil - it depends on the pH, soil texture and other soil properties.

"So, it really is important to keep testing soil and try to work out what is best for the type of soil and how farmers are working with it."

Mr Telfer said improved inquiry from EP farmers about lime spreading began in about 2016.

"It was a bit of a tipping point of tracking lime and it really took off on the EP after then," he said.

"In a localised area, I think the EP would be up there with anywhere in Australia for lime spreading."

Mr Telfer said the project was undertaken across a wide area because of changes in farming operations on the EP.

"We needed a wide variety of measuring points," he said.

"The way lime moves down through the soil depends on rainfall, sandy or clay soil, or what sort of tillage farmers are using.

"Ph is something which is common to soils but how it responds to lime applications and better management and different crop systems, varied quite widely."

Mr Telfer said farmers often needed to be convinced about input improvements and this program delivered science-backed data on understanding how soils responded to lime.

"There is science behind this program and it has allowed more numbers to confidently say to farmers, if you apply more lime, this is what may or may not happen."

The project looked at local areas which could traditionally be considered acidic soils.

Mr Telfer said increased crop production and less livestock and pastures, meant increased nitrogen fertilisers, and changes to soil acidity.

"This means, these areas which generally would not have been prone to acidic soils before, could actually be acidic," he said.

"The data showed on some instances, it was. It had not reached critical levels but if it is left, it will be.

"But farmers have grasped the economic and agronomic penalties of having soil suffering from toxic acidity."

Adelaide University researcher Ruby Hume was also involved with the soil acidity program and applied cutting-edge spectrometry-based techniques to see small amounts of lime in soil samples.

It shed some light about how much farmers need to lime following initial applications.

Ms Hume explored new methods to manage soil acidity during her PhD as part of a GRDC funded project aiming to address topsoil and subsurface acidity in No Till cropping systems.

"My research focussed on the use of mid-infrared spectroscopy as a new approach to measure and monitor acidity," she said.

"This method enabled undissolved lime to be measured down the soil profile."

Ms Hume believed this information was useful to understand if lime had moved into subsurface soil layer.

"It can also inform growers about how much lime remains in the soil profile to continue to treat acidity into the future, or if additional lime applications may be needed," she said.

Spectroscopy also offers a fast and effective way to measure soil pH, and can provide information about soil acidity at high spatial resolution, to improve the way acidity is managed throughout the profile.

"Once lime has been applied to an acidic soil, the next question often asked is 'what's next?' These new methods may help to answer this question," Ms Hume said.

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