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A-maize-ing!

By Robert C. Balling Jr., Ph.D.
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.

It’s 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 characteristics.

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 crop’s 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 (3819 bytes)

Figure 1. Simulated enhancement for a doubling of carbon dioxide.

What could possibly quash this eco-miracle? Temperature change—but 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 4C (7.2F) 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 4C (7.2F). 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 4C (7.2F) 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. It’s fed our families for centuries, and will help to feed the world in decades to come.

Reference:

Dhakhwa, G.B., et al., 1997. Maize growth: Assessing the effects of global warming and CO2 fertilization with crop models. Agricultural and Forest Meteorology, 87, 253–272.