Increasingly harsh drought conditions in the U.S. Midwest’s Corn
Belt may take a serious toll on corn and soybean yields over the next
half-century, according to research published today in the journal Science.
Corn yields could drop by 15% to 30%, according to the paper’s estimates; soybean yield losses would be less severe.
North Carolina State University’s Roderick Rejesus, associate
professor of agricultural and resource economics and a coauthor of the Science
paper, says that corn and soybean yields show increasing sensitivity to
drought with yields struggling in dry conditions in Iowa, Illinois, and
Indiana during the 1995-2012 study period.
“Yield increases are getting smaller in bad conditions,” Rejesus
said. “Agronomic and genetic crop improvements over the years help a lot
when growing conditions are good, but have little effect when growing
conditions are poor, like during droughts.”
U.S. corn and soybeans account for approximately 40% and 35% of
global production, respectively, making the results important to the
world’s food supply.
Using field data over an 18-year period, the researchers point to the
effects of vapor pressure deficit (VPD) on corn and soybean yields. VPD
includes temperature and humidity measures; extremes at either end of
this variable signify drought or too much water for crops. Akin to the
sweet spot on a baseball bat, the best VPD condition is a value in its
Some 29 climate estimates modeled in the paper suggest that VPD will
rise significantly over the next 40 years, bringing on more severe
The researchers ran the same tests using the Palmer Drought Severity
Index, another widely used measure capturing nationwide temperature and
humidity, and reported similar results. They also ran the same tests for
a broader group of Corn Belt states to include South Dakota, Nebraska, and Kansas. Those tests confirmed the results found in Iowa, Illinois, and Indiana.
Rejesus adds that crop densities may be one reason for the problem.
When plants are placed closer together, he says, it’s easier for bad
conditions to affect more plants. Crop simulations conducted in the
study supported this notion.
Rejesus says that research into more drought-resistant seeds or other
ways of combating sensitivity to drought is necessary because the
findings have strong implications throughout the food chain.
“There are a number of risk-management implications for farmers,” he
said. “Should farmers – 80% of whom already purchase crop
insurance – buy even higher levels of crop insurance? What kinds of
safety nets should be in place for farmers, if any? What happens to meat
prices when corn yields diminish? There are lots of trade-offs involved
in this issue.”