By DOUG SCHMITZ

Iowa Correspondent

AMES, Iowa — In a landmark study released by Iowa State University, researchers have said the overall effects on crops growing in wind farms appear to be positive.

“It’s unusual because we’re continuing the previous land use and we’re adding another,” said Gene Takle, ISU professor of agronomy, who has led a team of plant and soil scientists along with extension specialists to study the effects of wind turbines in agricultural areas since 2009.

Takle said the new land use was positive for the landowners where they were located, but the researchers wondered if it was the same for the farmers growing crops.

“We’re sort of double-cropping because these can be thought of two forms of energy production,” he said. “The Chinese do this when they plant soybeans in between horticultural crops. We’re planting turbines.”

He said wind blowing across a corn or soybean field without turbines creates a certain turbulence that carries moisture from the transpiring crop, which rises into the atmosphere and pulls down cooler, drier air. At night, the wind is calmer and the land cools.

According to Takle, turbines take some of the wind energy, slowing it down but increasing its turbulence so that it interacts with the crop more, possibly increasing evaporation from or moving carbon dioxide down into the crop.

“The biggest changes are at night and that’s because during the day, there’s a lot of chaotic turbulence, just because the sun is heating the surface and the wind is gusty,” he explained. “At night when it gets pretty calm, the crop cools down and if it’s a humid night, you start to get dew formation.

“If you add the turbines, it looks a little more like the daytime. So the dew formation is delayed and it may start to evaporate sooner.”

Moreover, because fungus and mold like a wet environment, he added the shorter wet period makes it less favorable for the growth of those pathogens. Takle said turbines also bring warmer air down to interact with the cool air near the surface throughout the wind farm, which inhibits dew formation.

“Satellites can measure surface temperatures and you can see little dots across the state of Iowa and locate every wind farm because they’re slightly warmer than the surrounding area,” he said. “So we know it has an effect that’s large enough to be seen there.”

On the negative side, Takle said there’s the tendency of higher temperatures occurring at night in wind farms.

“So the nighttime warming of the turbines is not a totally good thing,” he noted. “Nighttime temperatures have been going up over the last 40 years and are becoming a limiting factor for crop yields.”

In addition, noise is another negative factor of wind turbines, said Clarke McGrath, ISU agronomist and extension and on-farm research coordinator for ISU’s Iowa Soybean Research Center (ISRC).

“This is one we hear about fairly often, and it probably depends on where you live in relation to the turbines, the type of turbine and your perspective,” he said. “I do a lot of plot work in fields that have multiple wind turbines adjacent to them, some as close as maybe 300 yards, some up to around a half-mile away, and I can still hear them.

“It isn’t a really loud noise, but on a relatively calm day, if they are turning due to a higher elevation breeze, it’s nonstop and I could see where living close to them would quickly become annoying. I doubt that the crops care about the noise, but I do get livestock producers asking what it might do to animals. From what I read, it’s not clear yet what the impacts might be.”

McGrath said turbines on farmland may also effect land values – especially farmland adjacent to wind farms.

“From a crops perspective, I doubt that adjacent wind turbines would impact the price of farmland,” he said. “However, wind turbines on farmland have changed cash rental rates, in cases.

“In the regions I spend the most time in – south-central, southwest and west-central Iowa – the wind turbines and their access roads take up high flats, which is some of the more productive land on some of the tracts. So in some instances, the landlord adjusted the overall rent to reflect that.”

McGrath added, “When a wind turbine is put up, the traffic, the access roads and the footprint of the wind turbine and associated area takes some of the prime farmland in areas where I work. It is a small percentage of the land overall, but for a given field with wind turbines in it, losing that sort of land undoubtedly impacts overall production.”

Another issue is with aerial application, which he said has been a booming business the last decade, with fungicide, insecticide and cover crop applications as the primary drivers.

“Depending on the wind turbine’s placement and the pilot preference, part of all of fields with wind turbines may be inaccessible to planes and choppers,” he said. “Depending on what the need was in the field, and if it can be met with a high clearance rig – at the right time, with minimal traffic damage – the yield impacts could range from minimal to catastrophic.”

Takle said what he and his team would like to look at further is the result of wind movement through a farm as it slows and tends to move up, which could create clouds if the air is warm and moist – and potentially rain.

“Are wind farms a preferential location for cloud formation or something that’s going to provide more rain in an area beyond the wind farm?” he said. “We don’t know. We have some preliminary measurements that suggest that this is a real effect. Theoretically, yes, there should be an effect, but is it large enough to be measured or to be important?”