There is widespread concern that global warming will have a strong negative effect on crop yields. Recent research published in Proceedings of the National Academy of Sciences on historical maize yields across the U.S. Corn Belt suggests that a continuation of the historical yield trend will depend on a stable climate and continued farmer adjustments.

This research, conducted by Ethan Butler, postdoctoral associate in the Department of Forest Resources in the College of Food, Agricultural and Natural Resource Sciences at the University of Minnesota and his colleagues from Harvard University and University of California, Irvine, analyzes how both climate and management have influenced the increase in yields. Overall, the research shows farmers have adapted to historical climate change. The combination of changes in climate, primarily cooling of the hottest temperatures, and farmer adjustments, including earlier planting and planting longer maturing varieties, increased maize yield trends 28 percent since 1981.

"We wanted to add the farmer into the picture of how climate change will affect crops," said Butler. "Sometimes, it feels like climate change is a juggernaut that is going to trample our way of life. In this research we've shown that farmers have already made adjustments to better align their planting practices with historical climate changes, and we hope this can be a guide to changes in the future."

Butler and the research team used a statistical model to study how rainfed maize yields reported by the U.S. Department of Agriculture (USDA) are affected by temperature using three crop development phases: vegetative, early grain filling and late grain filling. They found that planting is occurring earlier and that the late grain filling phase lasts longer. At the same time, the hottest temperatures have cooled. The earlier planting and longer grain filling are primarily associated with management decisions, while the cooling of hot temperatures appears to be an unintended benefit of widespread planting of high-yielding modern cultivars.

"One of farmers' biggest decisions is what they plant and when they plant it," said Butler. "We are seeing that farmers are planting earlier -- not only because they have hardier seeds and better planting equipment -- but also because it's getting warmer sooner."

The research also suggests the adjustments farmers have made have increased yields more than they would have in the absence of the historical changes in climate. However, in the Corn Belt, this means accentuating a surprisingly beneficial climate trend rather than reducing damages from a harmful change. This implies farmers have proven adept at adjusting to environmental changes, but that these benefits may evaporate in a warming climate.

It is unclear whether these historical patterns of adaptation will be maintained in a hotter environment, but farmer decisions must be considered in future analyses of how crop yields will be affected by a changed climate. The team hopes that by studying farmer adaptations, which have received relatively little attention, they will help to improve concrete actions that can be taken to reduce damages from a hotter world in the future.

This research was funded by the Packard Foundation, the United States Department of Agriculture, and the National Science Foundation.