U.S. corn crop’s growing sensitivity to drought revealed

The new study by Stanford University reveals that while yields in the U.S. Corn Belt have increased overall – likely due to new technologies and management approaches – the staple crop has become significantly more sensitive to drought conditions.

Cost of bad conditions rising

“The good news is that new technologies are really helping to raise yields, in all types of weather conditions,” said study lead author David Lobell, the Gloria and Richard Kushel Director of the Center on Food Security and the Environment. “The bad news is that these technologies, which include some specifically designed to withstand drought, are so helpful in good conditions that the cost of bad conditions are rising. So there’s no sign yet that they will help reduce the cost of climate change.”

Changes in planting and harvesting practices

According to the Stanford researchers, despite concerns about resistant weeds, climate change and many other factors, the corn industry in the United States has set record yields in five of the last seven years. Likely drivers of these bumper crops include changes in planting and harvesting practices, such as adoption of drought-tolerant varieties, and changes in environmental conditions, such as reduced ozone levels and increased atmospheric carbon dioxide concentrations that generally improve the water-use efficiency of crops. As climate change intensifies, however, the cost to maintain crop yields will likely increase, according to the study.

Using county soil maps and satellite-based yield estimates, among other data, the researchers examined fields in the Corn Belt, a nine-state region of the Midwest that accounts for about two-thirds of U.S. corn production. By comparing fields along gradients of drought stress each year, they could identify how sensitivity to drought is changing over time.

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Wide range of soil moisture retention

Even within a single county, they found a wide range of soil moisture retention, with some soils able to hold twice as much water as others. As might be expected, there were generally higher yields for soils that held more water. They found yield sensitivity to soil water storage in the region increased by 55 percent on average between 1999 and 2018, with larger increases in drier states.

According to the researchers, the results made clear soil’s ability to hold water was the primary reason for yield loss. In some cases, soil’s ability to hold an increased amount of moisture was three times more effective at increasing yields than an equivalent increase in precipitation.

So, why have yields become more sensitive to drought? A variety of factors, such as increased crop water needs due to increased plant sowing density may be at play. What is clear is that despite robust corn yields, the cost of drought and global demand for corn are rising simultaneously.

Increased access to field-level yield data

To better understand how climate impacts to corn are evolving over time, the researchers call for increased access to field-level yield data that are measured independently of weather data, such as government insurance data that were previously available to the public but no longer are.

Power of satellite data

“This study shows the power of satellite data, and if needed we can try to track things from space alone. That’s exciting,” Lobell said. “But knowing if farmers are adapting well to climate stress, and which practices are most helpful, are key questions for our nation. In today’s world there’s really no good reason that researchers shouldn’t have access to all the best available data to answer these questions.”