By Dr John Kirkegaard, CSIRO Plant Industry
“What are the roots seeing?” is the question researchers
are asking to gain a fresh perspective into some puzzling crop responses
and to find ways to improve crop performance.
Recent research by a team at CSIRO Plant Industry, funded by the GRDC
Soil Biology Initiative, has provided insights into how crops respond
to direct-drill (no-till) farming systems.
Dr Michelle Watt used a “wheat-root’s view” approach
to explain the long-observed poor vigour of direct-drilled wheat in southern
Australia. Previous work had shown that inhibitory bacteria (Pseudomonas
spp.) were building up on roots of direct-drilled wheat, but the reason
Shared ground: a new wheat root (left) in close association with
previous season canola roots in a subsoil biopore.
Close examination of roots in the field combined with laboratory and
microscopy studies, showed that the wheat roots are slowed in the hard,
uncultivated soil as they are forced to find existing biopores and cracks
to penetrate the soil.
The slower growth allows bacteria to multiply to damaging numbers on
the slowgrowing root tips. These negative effects can be avoided by achieving
faster root growth by sowing early into warm soil, using deep points to
provide softer soil below the seed, or using wheat varieties with more
vigorous roots. Other potential benefits of faster growing roots are more
efficient nutrient capture and deeper soil penetration.
As the roots grow deeper into the soil profile to reach water for grain-filling,
they become even more reliant on biopores and cracks as the density and
hardness of the soil increases. Previous studies suggest that between
40 and 80 percent of roots in subsoils may be found in or near biopores.
Dr Margaret McCully is studying roots in these deep biopores in long-term,
no-till paddocks, and has made some surprising observations. The residues
of dead roots from up to two years of previous crops remain in many of
These residues include old water conducting tissues and, surprisingly,
numerous root hairs and other root surface material. Living roots of the
current crop intermingle with these residues.
The biopores also contain an array of soil microbes, as well as small
soil fauna and their nutrient-rich fecal material. Thus although subsoils
are generally thought to be low in organic matter and biological activity,
wheat roots confined to biopores will experience quite different conditions
to those that soil scientists traditionally measure.
As deep biopores provide the main zones for root growth in the subsoil,
the impacts of management on their formation, maintenance, utilisation
and the ability of roots to function effectively within them are of interest
For more information:
Dr John Kirkegaard, 02 6246 5080, email@example.com
GRDC RESEARCH CODE CSP329, program 4
North, South, West