The Complexities of Corn Production

Interesting National Geographic article: The story becomes more and more complicated as you read further on.

U.S. corn production is booming—but not for the reasons scientists hoped

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.

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.

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 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.

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

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.