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June 18, 2008
A novel technique with potential
to identify wheat cultivars that will perform well in drought
and compacted soil conditions offers hope to WA graingrowers.
The thin wax layer technique, pioneered in the USA, has been
further developed at The
University of Western Australia (UWA) to determine the
effects of soil physical constraints on wheat."
 Grains
Research and Development Corporation (GRDC) supported
Research Fellow, Dr Xinhua He (photo), of the UWA School of
Plant Biology, is assessing the hardpan penetration ability of
wheat roots, using a thin wax layer to simulate soil hardpans.
A hardpan is a high strength soil layer beneath the surface,
formed by the soil subsurface being compacted by machinery
traffic, tillage, stock trampling and pressure of overlying
soil.
Dr He said that wheat plants growing above a hardpan layer were
less able to access water and nutrients, leading to poor shoot
growth and reduced grain yield.
Of WA’s 18 million hectares of cropping land, one quarter is
susceptible to soil compaction and more than 40 per cent is
moderately susceptible, which indicates the magnitude of the
problem.
Former GRDC Professor of Agronomy at UWA and now of Charles
Sturt University, NSW, Professor Len Wade, in collaboration with
Dr Tina Botwright-Acuna of The University of Tasmania, are
supervising the research.
Professor Wade indicated Dr He’s research demonstrated that the
wax layer technique was a good measure of a wheat line’s ability
to handle soil physical constraint, as shown by the promising
relationship between penetration of the wax layer and root depth
in the field.
“Using the wax layer technique will identify lines better
adapted to hostile soils and help identify promising lines for
future WA breeding programs,” Professor Wade said.
Dr He assessed 24 wheat cultivars and breeding lines under
drought stressed and well watered conditions in controlled
environments.
Field experiments also related differences in root penetration
ability, through the wax layer technique, to wheat rooting depth
and above ground dry matter production in contrasting sandy
duplex and red clay soils, at the Department of Agriculture and
Food WA (DAFWA) Merredin Dryland Research Station.
Dr He indicated the sandy duplex soil had a hardpan at 20
centimetres and the red clay, with no hardpan, increased in soil
strength with depth, especially on soil drying, thereby
resisting root penetration.
Differences in root penetration in thin wax layers observed in
the laboratory were compared to rooting depth in the field to
determine if the wax layer method could reliably predict hardpan
penetration ability.
Wheat dry matter was weighed and the long, fibrous, seminal
roots on each plant which penetrated to depth were counted as a
measure of root penetration ability.
Dr He said EGA Bonnie Rock , Camm , Carnamah , Halberd, Janz,
Machete, Stiletto and Wilgoyne had superior root penetration
ability in well watered and drought stressed conditions.
Cranbrook, C18 and Karlgarin didn’t penetrate the wax layer and
died shortly after under drought conditions. Their inability to
access additional soil water from deeper layers demonstrated the
importance of root penetration ability in drought conditions.
Dr He said more work was needed to understand what mechanisms
drove hardpan penetration.
“Also, we need to determine consistency of trait expression over
soil types and identify genetic control of hardpan penetration
ability to select better varieties.
“Hardpan penetration ability should directly impact yield under
drought,” Dr He said. |
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