Key message

• The Australian Synchrotron is being used to unravel soil-plant root relationships and better inform nutrient management strategies.

Root distribution within soils is critical to plant growth and yield due to its regulation of water and nutrient uptake. However, roots are often referred to as “the hidden half” as they are difficult to study, being concealed in the soil.

For soils with constraints, such as sodic soils or nutrient-depleted soils, root distribution is especially important. For instance, in a bid to close the yield gap, growers on clay soils in eastern Australia are turning to deep banding of fertilisers such as phosphorus and potassium to address declining soil nutrient reserves in subsoil layers.

However, results in the field can be variable, ranging from substantial yield increases to no observable response, depending on soil type and fertiliser source. This variability is likely related, at least in part, to the ability of roots to explore and utilise the phosphorus. Until now, examining root behaviour in these and other soils has been difficult.

With investment from GRDC and in collaboration with the Australian Nuclear Science and Technology Organisation (ANSTO), several Australian universities are developing new approaches to examine root behaviour in soils using the Australian Synchrotron in Melbourne. Using this leading-edge technology, root distribution information will be simultaneously related to soil properties and nutrient availability.

About the synchrotron

A synchrotron accelerates electrons to almost the speed of light, producing radiation, including X-rays, with special properties. These X-rays can be used to examine the three-dimensional distribution of roots within soils without disturbing the soils and without removing the roots.

Although this has been possible using conventional X-rays in typical laboratories, a new faster and more sensitive approach at the Australian Synchrotron can examine roots in soil cores up to 20 centimetres in diameter – 10 times larger than previously possible – and down to considerable depths (50 to 100cm). Being able to examine root distribution in large soil cores allows more realistic and informative analysis.

Intact soil cores

Collecting soil cores from the field and relating root distribution to nutrient availability and organic matter will provide information critical for understanding how to close the yield gap in constrained soils, including sodic soils (where roots are unable to access subsoil water) and nutrient-depleted soils (where roots are unable to access nutrients at the correct time and place within the soil).

This work commenced in late 2020 but is already well advanced. It is hoped the techniques will be fully developed in the next year, after which work will commence with researchers around Australia to value-add to existing GRDC investments.

Access to the synchrotron facility has taken research forward in a way that would not have been possible if traditional methods had to be relied upon. Given how widespread soil constraints are across Australia, using this machine to understand how root distribution can be improved in these soils will inform nutrient management decisions and help close the yield gap for growers.

More information: Dr Peter Kopittke, University of Queensland, 07 3346 9149, p.kopittke@uq.edu.au; Professor Enzo Lombi, University of South Australia, 08 8302 5071, enzo.lombi@unisa.edu.au