Planting wind energy on farms may help crops

America's corn belt overlaps with its central "wind belt"—a wide swath of the midsection of the United States that is ideal for wind energy development-an intersection that could be good news for corn, new research suggests. With the tremendous growth in wind energy in the past decade, turbines often have been planted in or near cropland—leading both farmers and researchers to wonder what effect the rotating blades might have on corn, soy, and other crops. In traditional agriculture in many places, farmers grow trees along the edges of fields, a technique that slows the wind and stirs up the air, benefiting the crops in the field. Now researchers are studying whether wind turbines can have a similar effect—actually helping crops to grow. Some of the leading research is under way in the U.S. Midwest, heartland of the world's leading corn-producing nation, a place where blustery fields have been ideal for siting wind energy farms. The findings here could apply to many places around the world, wherever turbines and farms are near each other, although the effects on vegetation may vary by region or by crop. Mixing the Air One of the more obvious ways that wind turbines could help agriculture is by mixing up the air, getting more carbon dioxide (CO2) to the crops, since "the job of corn is to take up as much CO2 as it can," said Eugene Takle, an agricultural meteorologist at Iowa State University. Some of the other effects turbines could have on crops would be more complicated. For example, by causing the air to move, wind turbines could reduce the amount of dew on leaves at night. This would help reduce crop diseases, such as those caused by fungi, Takle said. That would be a welcome impact in the top U.S. corn-producing state, Iowa, where climate change has made the air more moist, making dew more common, according to a report this year commissioned by the Iowa state government. (Iowa was second to Texas in the United States in wind energy installed in 2011.) Another potential beneficial impact: Because turbines mix up the air and slow wind speeds, they also could also affect the temperature around them, making nights warmer and days cooler. Both these effects could help crops, making frosty nights less common, and reducing the number of sweltering days that stress plants. With this variety of effects, "we are finding it's more complicated than we thought," Takle said. But based on his work on how trees affect crops, Takle expects that "on balance, the effect would be positive." Revealing Turbines' "Wakes" To figure out what effect turbines might have on crops, Takle is collaborating with a team at the National Renewable Energy Laboratory in Golden, Colorado, led by atmospheric scientist Julie Lundquist. Lundquist has begun using "lidar"—like radar, but using light—to reveal the swirls of air in the long "wake" behind a wind turbine, like the waves trailing behind a boat. At an American Geophysical Union meeting in San Francisco last week, her team presented initial results from its first large set of measurements, which the researchers are still analyzing. Modern turbines are typically perched on tall towers about 250 feet (80 meters) high, and the strongest part of the wake stretches downwind from a turbine about two or three times the height of the tower, the lidar studies revealed. The swirling turbulence from the turbine spreads out as it travels downwind, the lidar study found. "We're still trying to figure out where, and in which circumstances, the wake hits the ground," Lundquist said. A Need for Answers The turbines' influence on temperatures could also have a downside for crops. A nighttime rise in temperature could increase the amount the plants respire—a kind of exhalation at nighttime, when plants release some of the carbon they took up from the air during the day. That could be a negative because the plants would take up less carbon, losing some of the benefits of their daytime growth. The possibility underscores the importance of the research for the agricultural community. Farmers for years have leased portions of their fields for wind turbines as a way to boost income, but they have wondered what effect it might have on crops, Lundquist said. "It's a big choice for farmers to make," she said, so they hope to start getting answers soon. The effects that wind turbines could have on wind and temperatures fit with a 2010 study led by atmospheric scientist Somnath Baidya Roy of the University of Illinois, which was the first published study of the weather around a wind farm. His study found that in southern California, nighttime temperatures were higher downwind from wind turbines. Roy agreed that the effects on crops will be complex, and "one good thing could offset another bad thing." "I think the frost protection effect for crops is going to be a really good thing," Roy said, adding that it might outweigh other effects. Because of the varied effects of turbines and the needs of different plants, Lundquist cautions that what may help Iowa corn might not help other crops in other places. "Wind energy offers us great potential for renewable energy," she said, "we just have to be clever and sensitive about how we deploy it."