Direct drilling - a wheat root's view

A new wheat root in close association with previous season canola roots in a subsoil biopore.

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 was unclear.

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 the pores.

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 to agronomists.

For more information:
Dr John Kirkegaard, 02 6246 5080, john.kirkegaard@csiro.au

GRDC RESEARCH CODE CSP329, program 4

Region North, South, West