By Emma Leonard
Looking at roots is a bit like trying to look at jellyfish; remove them from their habitat and their form changes considerably. To overcome this problem researchers at Adelaide University are the first in the world to use advanced scanning and computer technology to study roots in undisturbed soils.
"Roots are the hidden half of the plant and currently our understanding of their growth, especially in hostile soils, is limited," says Dr Annie McNeill. "In many respects we only have half an understanding of our crops."
Photo: Dr Peter Kolesik and Dr Annie McNeill.
Dr McNeill is supervising the project, working closely with colleague Dr Peter Kolesik. They have extracted intact soil cores, 15 centimetres in diameter and 50cm deep, of sand-over-clay soil from Wharminda on the Eyre Peninsula, South Australia. The top 20 to 30cm of sand was nutrient poor, while the remainder of the core was dense clay considered to be a physical barrier to root growth.
Canola was grown in the cores under glasshouse conditions, with or without the equivalent of 30 kilograms of nitrogen per hectare.
The nitrogen was introduced as fluid urea at 10, 20, 30 or 40cm deep. Some cores were kept moist, whilst others relatively dry, for the 16-week growing period. At five points during the trial period, the soil cores containing the growing canola plants were transported to the Queen Elizabeth Hospital where each core was passed through a CT scanner.
"Anyone who has had a CAT scan will have a better understanding of the type of images we are producing," explains Dr Kolesik. "This CT scanner allows us to take three-dimensional images of roots greater than 1 millimetre diameter, and shows us detailed information about the soil structure, which we do not see in disturbed cores or soil pits."
Using a computer program originally designed to map blood vessels, the researchers can use the CT image to measure root volume, surface area, length and the direction of growth.
"This is the first time we have been able to see roots as they really grow in the soil," says Dr Kolesik. This initial research, funded through the Department of Education Science and Training, found that roots do not necessarily behave as thought. Although they often followed loose soil and organic layers, they did not grow into cracks in the clay surface but went straight through the hard clay surface.
The roots proliferated at the depth of fertiliser placement. This suggests the current practice of shallow fertiliser placement on these sand-over-clay soils may be discouraging root exploration and subsequently affecting crop performance.
GRDC Research Code: UA 00062, program 4
For more information:
Dr Annie McNeill, 08 8303 7879
Dr Peter Kolesik, 08 8303 6529