For many Midwesterners, wind is an occasional nuisance. For farmers, though, the wind’s impact can be huge — drying out crops and eroding topsoil. Gusts big and small also complicate the application of chemicals, and that can be particularly costly.
By Perry Stoner
“If we have drift going off the field, that's product that (the farmer’s) lost and he's not getting the value that he paid for that product," said Greg Kruger, a crop systems specialist with the University of Nebraska-Lincoln. Plus, there are plenty of environmental concerns as well.
To better understand how wind affects chemical drift, Kruger and his research team have brought the wind inside arenovated swine barn at UNL'S West Central Research and Extension Center in North Platte, Neb. The new facility is only the second of its kind in the United States.
As a sprayer sends water through a 4-foot by 4-foot wind tunnel, the researchers try out dozens of nozzles, searching for the most efficient and effective chemical application methods. It starts with the droplet size coming out of the nozzle.
"We know that the smaller the droplet size, the greater the drift potential. The small droplets take longer to reach the ground," Kruger said. "So anytime we've got an air flow that's pushing those droplets, if it takes longer to get to the ground, it's going to move farther from the point where it was released."
The more force used to apply chemicals, typically the smaller the droplet size.
"We've done a lot of work in the field looking at different droplet sizes on the efficacy side, and if we get those droplets too large, a lot of times the pesticides don't work," Kruger said. "So there's a sweet spot in there so that we don't have a lot of drift, but yet we're still getting the control from that pesticide that we want."
Near the fan in the wind tunnel is a honeycomb-shaped attachment that keeps the 15-mph wind blowing as straight as possible. This introduces an element of physics to the tunnel and accuracy to the measurements: Each droplet sprayed in the tunnel is measured when it bends the light of the laser beam set up at the opposite end of the tunnel.
“The more that light bends, the smaller the droplet is,” Kruger said. “So it's a little bit opposite of what we would generally expect."
Using the laser beam and computer allows for great precision.
"The diameter of a human hair is about 140 microns," he said. "We're picking up about a tenth of a micron on that laser beam, so about 1,400 times smaller than what the diameter of a human hair is, is the size of the droplets that we're picking up."
The research is right on target for Kevin Wemhoff, who owns Vantage Agri Service in Otoe County in southeast Nebraska. Applying liquid chemicals makes up a large part of the business, especially this time of year. It's windy this time of year, too, and chemical application directions don't allow for much wind.
"Technically by most labels, it's 10 mph," he said. "Obviously, there are many, many days in Nebraska that it's over 10 mph, so trying to work within those parameters becomes extremely difficult. You try to do the best that you can with the challenges in front of you between weather and crops, and when guys are planting, and how much you have to do."
Wemhoff's high crop sprayer looks like a large transformer toy as the boom unfolds to a span of 90 feet. On board, sonar automatically adjusts the height of the boom to the rolling hills for optimum efficiency.
There are other options to counter the wind, too. Drift-retarding additives can help weigh down chemicals, and there are numerous types of nozzles to choose from to try to keep particle size larger.
While technology and information have improved efficiency, Wemhoff said, it's still important to continue to get better, especially for acreages that are close to urban areas or vineyards.
"You are always looking for more data, more information on how far particles move to give you the best idea of how to handle a field," he said.
That's what Kruger hopes will come from the research at the new wind tunnel facility in North Platte.
"There are a lot of different potential harmful effects that can come from a pesticide moving off target," he said. "And not every pesticide's the same, certainly. There's some that are much safer than others. So making sure that we don't have that off-target drift or off-target movement of those pesticides is critical to maintaining environmental and human health safety."
In addition to the machine that blows at 15 mph, a much larger machine can be attached, capable of winds up to 200 mph to replicate aerial chemical application.
"We've got engineering meets physics meets biology," he said.
After some initial testing, Kruger said he'll put plants in the wind tunnel for further research. He hopes the work will aid in drift-reduction technology, something the Environmental Protection Agency is already focusing on.
He compared it to the Energy Star program that helps consumers choose energy-efficient appliances.
“Similarly, this DRT policy will have labeling on products so that applicators, when they pick up a nozzle or they pick up a drift-reducing adjutant off the shelf to use with their application, they'll know that that product will have the ability to reduce drift," Kruger said.