Madison, Wisconsin
March 16, 2009
One of the most significant
developments in agricultural growth in modern times has been the
continuous and substantial increase in corn yield over the past
80 years in the U.S. Corn Belt.
This extraordinary yield advance has been associated with both
breeding of improved hybrids and the ability to grow them at
increased density. In a new study, published in the
January-February issue of
Crop Science, researchers have investigated the importance
of the effects of leaves and roots on this dramatic increase in
yield in the U.S. Corn Belt, and have found that the root
structure may be the key to understanding how these crops have
grown so efficient.
One associated change in the traits of these corn crops has been
a more erect leaf angle, which is known to create greater
efficiency in converting incident light to biomass. Over the
years, detailed studies have shown that the increase in total
biomass accumulated through sustained photosynthesis is one of
the key factors explaining the yield increase.
However, some studies have also shown that changes in the root
system also have an effect, as newer hybrids appear more
effective at extracting soil water from deep in the soil
profile. There is some evidence suggesting that hybrids with
narrower root angle have this capability. It is also plausible
that decrease in root angle combined with growing plants at
higher density could cause the increase in biomass accumulation.
Root systems with improved occupancy of the soil at depth can
extract more water to sustain biomass increase.
A team of scientists from Australia and the U.S.A., led by
Professor Graeme Hammer of The University of Queensland (UQ),
conducted this study on the leaves and roots of corn as part of
an Australian Research Council linkage project with Pioneer
Hi-Bred International. The project included scientists from UQ,
Queensland Department of Primary Industries, and Pioneer.
Their approach involved the use of virtual plant computer
simulation technologies. They modified an advanced crop model to
take account of known effects on crop growth associated with
varying leaf erectness and/or root system architecture. They
then simulated consequences on yield for representative sites in
the U.S. Corn Belt for a set of “hypothetical hybrids” varying
in leaf and root characteristics.
The study revealed that the historical corn yield trend and its
association with higher plant density was more likely related to
change in root system architecture than to change in leaf
erectness. While more erect leaf types could contribute to the
effect in some high-yielding situations, changes in root systems
to enhance capture of soil water at depth had the dominating
effect. Results for simulations conducted for hypothetical
hybrids that varied in root system characteristics were found to
be consistent with a set of field experiments that reported
yield response to density for hybrids released over the past 20
years.
“The use of dynamic crop models helped us to look beyond the
clearly visible differences among hybrids in this time series of
yield advance,” says Hammer. “It enabled us to focus on the
driving processes of crop growth that must be responsible for
these effects. It is clear that as we move forward we need to
look much harder at root systems and how they capture water.”
In the study, the extra amount of water required for the 6t/ha
historical yield increase was estimated as about 270mm. Further
research is required to determine whether this has now
positioned the corn crop near the limit of water resource
availability or whether there remains opportunity for yield
advance by further improvement in water capture.
The full article is available for no charge for 30 days
following the date of this summary. View the abstract at
http://crop.scijournals.org/cgi/content/abstract/49/1/299.
Crop Science is the flagship journal of the Crop Science Society
of America. Original research is peer-reviewed and published in
this highly cited journal. It also contains invited review and
interpretation articles and perspectives that offer insight and
commentary on recent advances in crop science. For more
information, visit
http://crop.scijournals.org
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