Research being conducted in South Australia could offer growers a simpler option for soil analysis and help deliver insights into more-effective liming techniques.

Ruby Hume, a PhD candidate in soil science at the University of Adelaide, is investigating the value of infrared spectroscopy for farm soil analysis.

Her study is helping assess the effectiveness of lime application techniques in treating soil acidification and acid stratification, as part of the GRDC Acid Soils SA investment being led by the South Australian Department of Primary Industries and Regions (PIRSA).

“Lime moves through the soil very slowly and PIRSA’s Rural Solutions SA team is testing a variety of lime sources, lime rates, incorporation methods and organic treatments at acidic sites across SA,” Ms Hume says.

“Infrared spectroscopy is ideal for measuring the effectiveness of lime movement in these trials because calcium carbonate has a very strong infrared signature.”

Spectral analysis highlights how the soils and crops are responding to the different treatment options.

“By analysing the infrared signature of soil samples, we can see how far the calcium carbonate has moved into the subsurface layers,” she says.

“It is a relatively simple, low-impact alternative to intensive soil sampling and analysis by a laboratory, which can be expensive and is not always practical.

Working at the different Acid Soils SA trial sites, Ms Hume takes soil cores and measures the level of calcium carbonate at various depths. She combines in-field spectroscopy using a handheld instrument with lab-based technology to confirm the accuracy of her field measurements.

The results are being used to develop a data model that will make interpreting future readings simpler and help identify the most-effective methods of using lime to manage SA’s significant problem with soil acidity.

PIRSA principal consultant Brian Hughes says Ms Hume’s research fits in well with the liming trials.

“The technology looks like it can provide quick and accurate measurements of lime levels through soil samples, which will be helpful as our trials progress and for longer-term acid soil management across the state,” he says.

Infrared spectroscopy also has the potential to measure a range of chemicals and nutrient profiles in both soil samples and leaf tissue. With appropriate data models, farmers could use it to assess soil properties such as organic carbon, carbonate and clay content, and pH buffering capacity.

Ms Hume says handheld infrared spectroscopy could inform a range of soil input decisions and measure the uptake of essential nutrients by crops.

She sees the potential for it to replace or at least complement laboratory soil analysis and even to be applied “on the go” in the field with further technology development.

“Handheld infrared spectroscopy has been growing in popularity over the last decade thanks to improvements in data processing and the equipment itself,” Ms Hume says.

“The technology is becoming more and more accurate, effective and affordable for industries like agriculture.”

Transferable mindset and technology

Combining her keen interest in spectroscopy and fascination with soil as a vital resource has led Ruby Hume to undertake a GRDC-supported doctor of philosophy on soil acidification.

“I was introduced to spectroscopy in my honours year at the University of Adelaide, and the scope of this technology continues to fascinate me as I learn more about the ways that it is being used in both soil and plant science,” Ms Hume says.

With a degree in natural resource science, Ms Hume studied variability of rangeland soils by analysing the ways that their spectral signatures differ. Although she does not have an agricultural background, she has brought insights and experience from investigating the properties of soils, and the ways that they can be measured and monitored, into an agricultural context.

Her move into the grains industry was based on a keen interest in soil science, while the chance to learn more about food production and improved farming systems also held great appeal. “I am conscious that many people from urban areas are quite removed from the agricultural industry, so I felt it was important to learn more about how our cropping systems work, and the challenges growers face.”

Her PhD study is being supervised by Associate Professor Luke Mosley and Professor Petra Marschner of the University of Adelaide, Dr Rhiannon Schilling of the South Australian Research and Development Institute and Dr Sean Mason of Agronomy Solutions as part of the GRDC-invested Acid Soils SA project, led by Brian Hughes from the South Australian Department of Primary Industries and Regions.

“We hope that this research will provide quick, simple and economic methods to detect acidity in the field and ensure that it is being managed effectively,” she says.

Ms Hume has an open mind about the future and is prepared to be flexible to see what opportunities may arise to which she can apply her skill set.

More information: Ruby Hume, 0419 828 939, ruby.hume@adelaide.edu.au