Graeme L. Hammer talks with
ScienceWatch.com and answers a few questions about
this month's Fast Breaking Paper in the field of Agricultural
Article Title: Can Changes in Canopy and/or Root System
Architecture Explain Historical Maize Yield Trends in the US
Authors: Hammer, GL;Dong, ZS;McLean,
G;Doherty, A;Messina, C;Schusler, J;Zinselmeier, C;Paszkiewicz,
Journal: CROP SCI, Volume: 49, Issue: 1, Page: 299-312, Year:
* Univ Queensland, Sch Land Crop & Food Sci, Agr Prod Syst
Res Unit, Brisbane, Qld 4072, Australia.
* Univ Queensland, Sch Land Crop & Food Sci, Agr Prod Syst
Res Unit, Brisbane, Qld 4072, Australia. (addresses have been
Why do you think your paper is highly
The paper addresses a salient, unresolved issue in agriculture, i.e., what
mechanisms have underpinned the continuous historical increase in maize
yield in the US Corn Belt? It provides some interesting insights on this
question and identifies a likely mechanism, which had previously not been
There have been few detailed relevant physiological studies, some good
studies on trait associations with yield advance, and no shortage of firmly
held opinions, but no previous attempt to put this into a quantitative
framework to test the various assertions.
This paper used a model-based hypothesis-testing approach to investigate
the relative importance of the effects of changes in leaf and/or root
factors. The approach involved the use of virtual plant computer simulation
An advanced crop model was modified to take into account known effects on
crop growth associated with varying leaf erectness and/or root system
architecture and the likely consequences on yield were simulated for
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.
"The work has general relevance to the need to continue
to increase crop productivity for global food security.
While the context of the study was the US corn belt, the
findings have far more general implications."
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.
Does it describe a new discovery, methodology, or synthesis of
This paper is an integrating synthesis of knowledge that has generated new
The use of dynamic crop models helped us to look beyond the clearly visible
differences among hybrids in this time series of yield advance. It enabled
us to focus on the driving processes of crop growth that must be
responsible for these effects.
Prior to this work the dominant opinion was that improvements in light-use
efficiency associated with leaf erectness underpinned the long-term yield
improvement of maize. However, this had not been evaluated quantitatively
in comparison to other possibilities or as a component of a more integrated
The work reported in this paper demonstrated that a more plausible
explanation for yield improvement is access to additional water through
enhancements in root system architecture.
The improvements in light-use efficiency via changes in canopy architecture
made a smaller but important contribution and thus had a secondary role.
The changes in leaf angle were readily observable, so working on these
trait phenotypes was easier.
Tackling the root question is now more firmly justified than was the case
prior to this work. It does not make the work any easier, but it certainly
more strongly motivates work on the root system.
Would you summarize the significance of your paper in layman's
The paper suggests that improvements in the ability of maize crops to
capture additional water from the soil via changes in root system
architecture is more likely to explain the historical yield advance in the
US corn belt than the more readily observed changes in canopy architecture
(such as leaf erectness) and any associated effects they may have on
enhanced efficiency of use of light energy. This provides valuable insight
as to potential avenues for future crop improvement.
How did you become involved in this research, and were there any
problems along the way?
I became involved in this research through a long-standing research
collaboration with scientists at
Pioneer Hi-Bred International that aimed at
developing and evaluating modelling capability to underpin novel
approaches to crop improvement by identifying critical adaptive traits,
particularly for the efficient use of water.
There were no major problems along the way, but we navigated many "dry
gullies" as ideas were developed and tested over the years of this
Where do you see your research leading in the future?
It is clear that, as we move forward, we need to look much harder at root
systems and how they capture water. In our study, the extra amount of water
required for the 6t/ha historical yield increase was estimated as about
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
Beyond the specific issue, we have developed confidence and the modelling
tools required for the more general use of model-based analyses in
interfacing with plant breeding. Developing and applying this capability
offers many opportunities and will be a major theme into the future.
Do you foresee any social or political implications for your
This work has general relevance to the need to continue to increase crop
productivity for global food security. While the context of the study was
the US Corn Belt, the findings have far more widespread implications.
Graeme Hammer, Ph.D.
Professor in Crop Science
School of Land, Crop and Food Sciences
The University of Queensland (UQ)
Brisbane, Australia Web | Web
RADIATION USE EFFICIENCY; ANTHESIS-SILKING INTERVAL; DIFFERENT WATER
REGIMES; GRAIN-YIELD; DROUGHT TOLERANCE; KERNEL KEYWORDS: NUMBER; TROPICAL
MAIZE; LEAF NITROGEN; PLANT-DENSITY; STAY-GREEN.