For the first time, researchers have measured the health risk of manure irrigation by conducting in-field experiments in Wisconsin.
The results show that the chance of getting sick from manure being irrigated is quite low – even when someone is in close proximity, said Mark Borchardt, a microbiologist and researcher with the U.S. Department of Agriculture.
As part of a study paid for by the state Department of Natural Resources, Borchardt and other researchers went to three farms in different parts of the state and measured the amount of microbes in the air at various distance points from an active manure irrigator.
“Going out and gathering empirical data hadn’t been done before,” Borchardt said. “We weren’t just trying to guess something in a lab or wind tunnel.”
In Wisconsin, where manure irrigation is a hot-button issue, he said interest in the result of his study is running high. The work was recently sent to a work group that is considering putting stricter statewide regulations in place.
“The question for policymakers is now decide if that’s an acceptable risk,” Borchardt said. “One level is very, very low risk while the other one is higher. We went with those two benchmarks since those are the standard ones out there.”
Currently, 14 concentrated animal feeding operations or CAFOs in Wisconsin use manure irrigation. Others, including John Pagel, owner of Pagel’s Ponderosa Dairy in Kewaunee, are considering the idea.
Pagel runs the state’s largest family-owned dairy and would be the first in Kewaunee County to use manure irrigation. He filed a petition with the DNR asking for approval to use an irrigation system to irrigate some of the 67 million gallons of manure produced annually on his dairies.
The effluent run through the irrigator would be what’s left over after the manure is run through two separate cleaning systems, including a biodigester and a nutrient recovery system that removes nitrogen and phosphorus, Pagel said.
“It will be mostly water coming out with some potassium,” he said. “A chemical analysis of the digested manure showed no signs of the common pathogens like E.coli. Most of those pathogens are killed through the biodigesting process.”
Pagel and other irrigation supporters said the practice, which uses pipelines and irrigation systems, allows for precise application and reduces runoff because the liquid can be applied while crops are in the field. Groundwater contamination would be prevented, too, because the crops would take up the nutrients before it moves deep into the soil.
“Right now, we can only spread two times a year. With this, we can apply it to growing crops,” he said. “It’s better for the plant and safer for the ground since smaller amounts are being applied at one time.”
Pagel plans to also use large drop nozzles, cutting down on possible drift.
The practice is also less expensive than the traditional method of trucking the manure to the field and then applying it with a manure spreader. Also, there would be less wear and tear on the roads.
In Borchardt’s study, researchers looked for the presence of microbes commonly found in manure, including E.coli, salmonella, cryptosporidium and giardia. Borchardt said the microbes do not live long in the air since heat and sunlight kill them.
The research was arduous and challenging, Borchardt said. Researchers measured the amount of microbes in the air at various lengths ranging from 100 feet to 750 feet downwind from both a traveling gun irrigator and a center pivot irrigator at three working farms.
“What sets what we did apart is that we did our research in real-life conditions and in real weather,” he said.
Next, researchers took a statistical approach to predict what would happen downwind in different weather and wind conditions. Finally, they did a risk assessment looking at how much of a certain microbe could be ingested before someone became sick.
“We were then able to estimate risk based on distance and weather. There’s no disputing our findings,” Borchardt said. “Risk levels go down with distance and the wind speed plays a role.”
Borchardt knows the study has its detractors, some of whom were at a meeting March 15 in Luxemburg where he presented an overview of his team’s work.
“People say we didn’t look at odor, we didn’t look at runoff or drinking water, but we needed to have a defined area of risk for our study and went with microbes in the air,” he said. “We couldn’t look at everything and this was a good starting point.”
When asked at the March 15th meeting to share his personal feelings about the potential for problems, Borchardt, who usually gathered the readings at the location closest to the manure irrigator, said, “I’m fine with the risk level.”