By Robert C. Balling Jr.,
Arizona State University
America loves its corn, and Americans
were in love with corn long before the arrival of Columbus and company 500 or more years
ago. From breakfast cereals to porterhouse steaks to adult beverages, corn is a
significant part of our daily diet.
It may well play an important role in
our future, too. Corn-burning stoves are an innovative, if not yet popular, heating
source. And the dream of one day using corn products to fuel our cars is still alive in
the minds of futurists.
Its no surprise, then, that
many scientists wonder how corn will fare in a world of elevated atmospheric carbon
dioxide (CO2) levels.
Among the curious were four
scientists from North Carolina State University and the National Oceanic and Atmospheric
Administration. The team used two popular crop models to assess, among other things, the
effect of elevated atmospheric CO2 concentrations on corn yields and plant
As they reported in Agricultural
and Forest Meteorology, the CERES (Crop Estimation through Resources and Environmental
Synthesis) and EPIC (Erosion/Productivity Impact Calculator) models were run for a 1°
latitude by 1° longitude grid cell in the central Piedmont area of North Carolina. They
used the actual daily weather records from 1949 to 1988 to drive the crop simulations;
these records included daily maximum temperature, minimum temperature, precipitation, and
an estimate of solar radiation.
As with so many other plants, corn
seems to love elevated CO2. When the atmospheric carbon dioxide is doubled, the
CERES model produces an increase in overall yield of 18 percent, while the EPIC model
generates a slightly lower 14 percent rise. Figure 1 illustrates that most plant
characteristics show an enhancement of between +10% and +20%. But the greatest enhancement
comes in how well plants make use of the water they take in. Called the water-use
efficiency term, it is defined as plant production per unit of water consumption. The corn
crops water-use efficiency increased by 29 percent in the CERES model and 28 percent
in the EPIC model when CO2 is doubled. A partial closure in the leaf stomata is
responsible for the 8 percent reduction in evapotranspiration, and when combined with the
yield increases, the future corn crops water-use efficiency soars. Imagine that!
Elevated CO2 made the crops in these models grow larger and more vigorously
both above and below ground. It increased the overall corn yield. And it produced plants
that were significantly more water-efficient.
Figure 1. Simulated
enhancement for a doubling of carbon dioxide.
What could possibly quash this
eco-miracle? Temperature changebut only of a specific kind.
The North Carolina team found that a
large increase in local temperature could neutralize the biological benefits of increased
CO2. As the CERES and EPIC models confirmed, if the mean temperature of central
North Carolina shoots up by 4°C (7.2°F) as CO2 is doubled, we can forget
about any benefits.
Corn crops suffer the most if the
mean, minimum, and maximum temperature all increase by 4°C (7.2°F). But the negative
effects are not nearly so bad if the rise in mean temperature is associated more with a
rise in the minimum temperature than the maximum.
When they allowed the minimum
temperature to increase three times faster than the maximum, maintaining the overall 4°C
(7.2°F) temperature increase, they found the corn was 10 percent better off than in the
equal day-night warming case.
Given what we already know about the
future, this is excellent news. Atmospheric CO2 concentration is rising, so
corn production will improve. Morning temperatures are generally rising much faster than
afternoon temperatures; again, this general drop in diurnal temperature range seems to
favor better corn production.
So slather another pat of butter on
that sweet, steaming piece of American tradition. Corn is the crop of the future.
Its fed our families for centuries, and will help to feed the world in decades to
G.B., et al., 1997. Maize growth: Assessing the effects of global warming and CO2
fertilization with crop models. Agricultural and Forest Meteorology, 87,