Iowa's farmers have benefited overall from climate change by adapting their practices, Iowa State University Professor Gene Takle told a United Nations conference last week.
The ongoing drought that cut into corn yields this year "underscores we are in fact vulnerable to these extreme events," Takle said in an interview, although his research suggests climate change's broader impact on corn production in Iowa has been favorable.
Takle said the primary impact of climate change on Iowa's grain producers has been increased rainfall.
In Cedar Rapids, Takle said, the period from 1890 through 1950 only saw two years with over 40 inches of rain. In the 60 years that followed, 18 years have had at least 40 inches of rain.
More significant for agriculture, Takle said, has been the shift toward more rainfall in the first half of the crop season.
The increase in early-season rainfalls has allowed crops to begin the season with more topsoil and subsoil moisture. Takle said farmers have taken advantage of the abundance of groundwater by planting seeds more densely, resulting in more plants and higher yields per acre.
Seed planting density in cornfields has grown to an average of 35,000 seeds per acre from about 20,000 seeds per acre 30 years ago, Takle said.
Iowa has also seen a significant increase in the number of weather events with 1.25 or more inches of precipitation in a 24-hour period. Such events tend to exceed the ability of soils to absorb the rainfall, causing more floods and erosion.
"The gradual increase in precipitation is not the metric we need to look at," said Takle, a professor of agronomy and geological and atmospheric science. "We need to look at the extreme events."
As climate change has lengthened the growing season in the past several decades, Takle said farmers have tended to opt for corn hybrids that take longer to mature but produce greater yields.
Farmers have also responded to more frequent precipitation early in the planting season by buying larger planters that enable them to plant corn more quickly during the smaller windows of time when fields are dry enough to plant.
"The change in precipitation has really benefited corn productivity," Takle said. He offers the example of the 2011 growing season, when Iowa's corn crop received very little rain after July 4. The corn crop was excellent anyway because of the abundance of subsoil moisture from early season rains.
Takle is director of the ISU climate science program. He is working with the USDA to prepare an assessment of the impact of climate change on agriculture requested by Congress.
Takle told conferees that the strong corn profits Iowa farmers have generated due to high prices in recent years have helped them adapt to climate change. Strategies have included the installation of more drainage tile in fields to reduce the impact of extreme rainfall events, and buying more drought-tolerant seed hybrids.
Research is progressing on other farming strategies to adapt to climate change, Takle said, such as increasing soil carbon that will allow the soil to store more moisture and nutrients.
Iowa's soil remains at about a 12-inch moisture deficit due to the drought. While Takle says it's impossible to draw a direct link to climate change, he said it's consistent with the increase in extreme swings in weather that climate change is producing around the world.
Takle was part of a three-member panel organized by the United States Department of Agriculture to speak Nov. 28 at the United Nations climate conference in Doha, Qatar.
One of the USDA's interests in addressing the conference was a perspective in some other countries that the United States is not reacting to climate change because it has not felt its impacts as much as other regions of the world, Takle said.Takle was the only academic profession on the three-person panel. The other members were from the USDA and the private sector.