Corn Yields Are Growing More Sensitive To Heat And Drought

According to Stanford research U.S. corn yields are growing more sensitive to heat and drought. Farmers are faced with difficult tradeoffs in adapting to a changing climate in which unfavorable weather will become more common.Corn Yields Are Growing More Sensitive To Heat And Drought

The study, which appears in the journal Science, was led by Stanford’s David Lobell, associate professor of environmental Earth system science and associate director of the Center on Food Security and the Environment. “The Corn Belt is phenomenally productive,” Lobell said, referring to the region of Midwestern states where much of the country’s corn is grown. “But in the past two decades we saw very small yield gains in non-irrigated corn under the hottest conditions. This suggests farmers may be pushing the limits of what’s possible under these conditions.”

He predicted that at current levels of temperature sensitivity, crops could lose 15 percent of their yield within 50 years, or as much as 30 percent if crops continue the trend of becoming more sensitive over time.

As Lobell explained, the quest to maximize crop yields has been a driving force behind agricultural research as the world’s population grows and climate change puts pressure on global food production. One big challenge for climate science is whether crops can adapt to climate change by becoming less sensitive to hotter and drier weather.

“The data clearly indicate that drought stress for corn and soy comes partly from low rain, but even more so from hot and dry air. Plants have to trade water to get carbon from the air to grow, and the terms of that trade become much less favorable when it’s hot,” said Lobell, also the lead author for a chapter in the U.N. Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report, which details a consensus view on the current state and fate of the world’s climate.

Rain, temperature, humidity

The United States produces 40 percent of the world’s corn, mostly in Iowa, Illinois, and Indiana. As more than 80 percent of U.S. agricultural land relies on natural rainfall rather than irrigation, corn farmers in these regions depend on precipitation, air temperature and humidity for optimal plant growth.

According to the research, over the last few decades, corn in the United States has been modified with new traits, like more effective roots that better access water and built-in pest resistance to protect against soil insects. These traits allow farmers to plant seeds closer together in a field, and have helped farmers steadily raise yields in typical years.

But in drought conditions, densely planted corn can suffer higher stress and produce lower yields. In contrast, soybeans have not been planted more densely in recent decades and show no signs of increased sensitivity to drought, the report noted.

Drought conditions are expected to become even more challenging as temperatures continue to rise throughout the 21st century, the researchers said.

Lobell said, “Recent yield progress is overall a good news story. But because farm yields are improving fastest in favorable weather, the stakes for having such weather are rising. In other words, the negative impacts of hot and dry weather are rising at the same time that climate change is expected to bring more such weather.”

Lobell’s team examined an unprecedented amount of detailed field data from more than 1 million USDA crop insurance records between 1995 and 2012.

“The idea was pretty simple,” he said. “We determined which conditions really matter for corn and soy yields, and then tracked how farmers were doing at different levels of these conditions over time. But to do that well, you really need a lot of data, and this dataset was a beauty.”

Lobell said he hopes that the research can help inform researchers and policymakers so they can make better decisions.

“I think it’s exciting that data like this now exist to see what’s actually happening in fields. By taking advantage of this data, we can learn a lot fairly quickly,” he said. “Of course, our hope is to improve the situation. But these results challenge the idea that U.S. agriculture will just easily adapt to climate changes because we invest a lot and are really high-tech.”

Lobell and colleagues are also looking at ways crops may perform better under increasingly hot conditions. “But I wouldn’t expect any miracles,” he said. “It will take targeted efforts, and even then gains could be modest. There’s only so much a plant can do when it is hot and dry.”

Laura Seaman is the communications and external relations manager for Stanford’s Center on Food Security and the Environment, a joint program of Stanford’s Freeman Spogli Institute for International Studies and the Stanford Woods Institute for the Environment.



Climate Change in Nebraska Requires Planning for the Future of Agriculture, Experts say

Nebraska is in the western cornbelt and in a marginal rainfall area to begin with, John Hansen, president of the Nebraska Farmers Union, told the Legislature’s Agriculture Committee on Tuesday.

“A little change in not only the amount but the timing of moisture has huge, huge consequences both on grain production but also livestock,” he said.

Hansen and climate specialists were testifying on a bill (LB583), introduced by Sen. Ken Haar of Malcolm, that would beef up the state’s Climate Assessment Response Committee’s membership, reporting and communication duties to better prepare for changes.

The country is in the worst national drought in 50 years, and the past year was the warmest and driest ever in Nebraska, they said.

“We’re sitting here with virtually no subsoil moisture. We couldn’t possibly be more vulnerable as we go into this next growing season,” Hansen said.

Not dealing with the changes and volatility is not a prudent path forward, he said.

Haar’s bill would add a member of the High Plains Regional Climate Center at the University of Nebraska-Lincoln to the Climate Assessment Response Committee. It would require the committee to report to the governor the impacts of climate change on Nebraska and how to prepare for it, and facilitate communication to address climate change impacts and response strategies.

Haar told the committee 34,000 daily record highs were set last year at weather stations across the country. The country also had the second most weather extremes on record, behind 1998.

“We need to start considering how to adapt to the impacts of the changes that are occurring and work diligently to ensure that we do not make the problems even worse,” he said.

Clint Rowe, professor in UNL’s Department of Earth and Atmospheric Sciences, said the state can no longer afford to debate if human-induced climate changes are happening. They are.

In September, record low amounts of sea ice were reported, he said.

“We’re loading the dice toward more extremes,” he said.

The 2012 drought was an eye opener, said Michael Hayes, director of the National Drought Mitigation Center and a member of the Climate Assessment  Response Committee. The warm and dry weather beat out the dust bowl years of the 1930s.

Across the country, economic losses from the drought are estimated between $35 billion and $77 billion.

While scientists for the National Oceanic and Atmospheric Administration have said the drought falls within the context of natural climate variability, he said, the heat combined with the dryness in 2012 gives a glimpse of what future climate extremes might look like in Nebraska. And all climate models indicate increased temperature in the future.

Hansen said that although Nebraska has always been a state of weather extremes, it seems the volatility is increasing.

“We need to develop the tools we need to manage that volatility,” he said.

How does the state use less water? How does it store water more efficiently? How does it change its cropping patterns? How can it get more use out of the moisture it has?

One reliable study says Nebraska will be too far south to grow corn by 2050.

“Whether it’s 2050 or whether it’s 2080, whenever it is, it behooves us to be thinking about what it is that we do to develop appropriate kinds of crops and strategies to deal with the kind of weather that we’re getting,” he said.