Study finds that climate change is hurting soybean yields

Even during good years, our nation’s soybean farmers are, in essence, taking a loss. That’s because changes in weather patterns have been eating into their profits and taking quite a bite: $11 billion over the past 20 years.

This massive loss has been hidden, in effect, by the impressive annual growth seen in soybean yields thanks to other factors. But that growth could have been much greater—30% higher—if weather variations resulting from climate change had not occurred, says a study published last month in Nature Plants.

“We are still making yield gains because of breeding and other strategies, but those numbers aren’t as big as they could be,” says lead author Shawn Conley, a University of Wisconsin-Madison agronomy professor and UW-Extension soybean and wheat specialist.

In the study, researchers isolated the impacts of changing temperature and precipitation on soybean yields in a much more precise way than previously done. While earlier approaches relied on estimates, Conley’s team used data gathered from their own field trials, giving them access to reliable and consistent information about the genetics of the soybeans being grown, the management practices being used and the weather the fields saw throughout the growing season. Spyridon Mourtzinis, a post-doctoral fellow in Conley’s lab with expertise in statistics, took care of the number crunching.

“Spyridon removed the effects of the management strategies and genetic improvements, so that we could just focus our analysis on the impacts of weather variability,” says Conley.

Averaging the data across the U.S., the researchers found that soybean yields fell by around 2.4% for every one-degree rise in temperature. Considering the impacts of both temperature and precipitation together, they found quite a bit of variability among soybean-growing states, yet a trend emerged.

In Wisconsin and most other northern states, including South Dakota and Minnesota, the changes in climate factors actually led to higher soybean yields. Wisconsin, for instance, saw an increase of 17.5 kg/hectare/year over the 20 years studied. At the same time, most soybean-growing states further south, including Ohio, Arkansas and Kentucky, experienced decreases in yields.

These divergent responses have to do with historical norms. In colder northern states, soybeans seem to be enjoying the new warmer weather, whereas in states further south—where conditions had previously been fairly ideal—the additional heat is causing stress.

Because the states with the biggest yield losses are also our nation’s biggest soybean producers, the national impact comes out to a 30% yield loss overall, which amounts to an $11 billion economic loss, over the past 20 years.

Now that the impacts of weather variations are becoming clearer, the next step is to help growers minimize the negative impacts. Farmers have already been incorporating some strategies—earlier planting, no-till practices and growing later maturing soybeans—into their farming practices. The researchers’ goal is to further improve those strategies by producing region-specific suggestions that account for weather patterns at different times of the growing season.

Only then, says Conley, can the full potential of soybean yields be realized.