The Corn Belt, which spreads across the middle of the United States from Indiana to Nebraska, is in many ways a marvel of modern agricultural science: It grows more than a third of the world’s corn, and produces 20 times more than it did in the 1880s on just about double the land area.
Historically, most of those gains in yield have been achieved through improved farming methods and selective breeding of corn. In recent decades, genetic engineering—which allows more precise tinkering with genes than conventional plant breeding—has been thought to have increased yields a lot. Most of the American crop is now genetically modified in one way or another.
But according to a new study published in the Proceedings of the National Academy of Sciences, over the past 15 years, the primary driver of growing corn yields has been another factor entirely: the longer growing seasons and mild weather promoted by climate change.
That is not necessarily good news, scientists hasten to add. As the world keeps warming, conditions in the Corn Belt may become less favorable to corn, endangering further gains.
More importantly, scientists have been counting on genetic engineering as a prime tool to help keep yields increasing in the future, a necessity for a world that must continue to produce enough food for a growing population. In the Corn Belt, the new study suggests, that tool hasn’t been as useful as they thought.
“We’re going to need to be really creative in order to keep yields up,” says Patricio Grassini, an agricultural scientist at the University of Nebraska-Lincoln who was one of the authors of the new study.
The corn belt of success
Since the 1930s, corn production has risen steadily, as vast scientific resources have been poured into improving yields and crop productivity has been pushed closer to theoretical limits. Growers learned to pack more plants into smaller areas, fine-tuned fertilizer timing, and rotated crops to make soils healthier. Crop breeders developed plants that could grow more closely together, or turn their leaves to the sun, or mature earlier in the season.
In the late 1990s, they began to use even more sophisticated technologies to tweak plants' genetic makeups more precisely. Scientific enthusiasm for new genetic tools was high: For many, the thinking was, “Don’t worry about food security, our crop yields are going to go up to the sky,” says Grassini.
At the same time, the world’s climate began to change, the result of unchecked fossil-fuel burning. Many regions began to feel those effects, such as super-intense rain, unexpected heat waves, or even just over-warm temperatures. Today, climate changes are causing major problems for growers in many parts of the world.
But so far, its impacts on the middle and northern end of the Corn Belt seem to have favored corn growth. Slightly longer seasons, particularly in the spring, a crucial time when plants flower, and longer stretches of temperate weather during the “grain filling” period—the time after kernels form—have helped farmers bump up their yields over the years, the new study concluded.
But how much did climate, genetics, and agricultural adjustments each factor in? Historically, studies have found that in fields set up for success—with plenty of water and nutrients—better genetics play a big role in pushing up yields.
But when researchers focused on the highly productive corn fields of Nebraska from 2005 to 2018, the results surprised them. Genetic tweaking contributed only about 13 percent of the total rise.
“All these promises about quantum-leap gains have fallen short of reality,” Grassini says.
Better farm-management practices, like fertilizing effectively or packing more plants into a field, made a much bigger difference, accounting for about 39 percent of the overall bump. Together, genetic and agricultural improvements added about 85 pounds of corn per acre every year to farmers’ hauls.
The biggest effect came from the gentle, favorable climate conditions of the past few decades, which were responsible for just about half of the overall gains—about 80 pounds extra per acre per year.
Success hides risks
Nathan Mueller, an agriculture researcher at Colorado State University who was not involved in the new study, warns that the mild weather conditions that have helped corn are unlikely to be permanent. If climate continues to warm, as expected, there may soon come a time when the balmy conditions become sweltering, droughts and storms intensify, and weather systems become less predictable—all effects cataloged as real possibilities by the most recent U.S. National Climate Assessment.
“It’s really important to tease apart the source of different risks to yield so that we know what tools we need to use to sustain current growth, or to counteract declines” and better insulate against climate risks, Mueller says.
Why have weather conditions been so mild in the region, while climate change wreaks havoc elsewhere? Some of it may be luck, Mueller says. But some of it is due to the huge blanket of largely irrigated agriculture itself: The region is so vast, and so uniform in its planting practices, that it has in fact created its own climate. Mueller and his colleagues found that the hottest summer temperatures across the region have actually cooled slightly over the last century, the opposite pattern of almost anywhere else in the world.
That’s primarily because all the corn plants growing in synchrony act as a giant air conditioner. They suck up water through their roots as a liquid, then transpire it through their leaves as a vapor. That transformation from liquid to vapor requires heat, which is extracted from the surrounding air. With so many plants transpiring at once, summer temperatures over the region end up cooler than they would otherwise be.
But “it’s a short-lived celebration,” says Ariel Ortiz-Bobea, a climate and agricultural economist at Cornell University. The hotter it gets, the less effective that natural air conditioning is. And the overall effect depends on the availability of copious irrigation water—which in many Corn Belt states, including Nebraska, comes from the dwindling Ogallala aquifer. It’s highly possible the irrigation patterns may have to change as that resource disappears.
“Thinking about the central plains of the U.S., they better not hang their hat on irrigation, and its climate benefits, for the future,” Ortiz-Bobea says. “The transition is coming, with or without climate change—but climate change is speeding it up.”
When it comes to the challenge of feeding a growing population, increasing crop yields isn’t always the most important strategy, says Claire Kremen, an ecologist at the University of British Columbia—especially in the Corn Belt, where 90 percent of the crop goes to make ethanol for fuel and to feed animals rather than people. The heavy use of fertilizers, ancient groundwater, and pesticides required to maximize short-term production may endanger agriculture’s potential in the long term, she says.
But for Grassini, understanding how much farther yields can go could help clarify where farmers can, and should, focus their energies.
“The fact that we didn’t find too much increase in the yield potential doesn’t mean we shouldn’t keep trying” to make it better. But it’s crucial to recognize that dreams of squeezing more and more food out of genetic improvements “aren’t enough on their own to meet the challenge of climate change.”