VIDEO: Scientists, farmers study impacts of winter manure on watersheds

BROOKINGS, S.D. -- With this spring's warm weather, many livestock farmers around the region will likely start spreading manure in the next few weeks.The topic of winter manure application is controversial, but some livestock operators think wint...


BROOKINGS, S.D. - With this spring’s warm weather, many livestock farmers around the region will likely start spreading manure in the next few weeks.
The topic of winter manure application is controversial, but some livestock operators think winter applications of dry products and so-called “brown snow” is better than the alternatives.
South Dakota has a clause in its general permit for livestock producers that allows winter application of manure on frozen or snow-covered ground, with restrictions based on topography and proximity to waterways. The general permit is in the process of being reviewed for changes.
Scientists at South Dakota State University are studying the implications of runoff on crop production and the environment.
“We’re trying to quantify that,” says Joe Darrington, a South Dakota State University Extension livestock environment associate. He is a veterinarian and holds a bachelor’s degree in agricultural engineering.
Cautionary principle
The particular SDSU study has roots in the 1990s, with related studies to find the upper limits of what manure can be safely applied, without causing environmental problems, especially with phosphorus.
Mike Schmidt of Dell Rapids, S.D., now the District 2 director of the South Dakota Farm Bureau, was one of the people who helped SDSU become more active in studying the issue, and is a cooperator on the current study.
Schmidt, 69, has a 150-head cattle operation that is not big enough to be a concentrated animal feeding operation (CAFO), but sees the issue as important for the Northern Plains livestock industry, because of its short growing season and manure application period. He says the experiments have been set up to meet international scientific protocols.
The current thread of the study started in 2010. It has so far provided uneven data because of the lack of winter snow or equipment. The winter manure application study could help further guide regulations for CAFOs.
An earlier part of the project established a phosphorus index, which is incorporated into the general permit, and practices approved by state officials and the Natural Resources Conservation Service.
“The Environmental Protection Agency tends to regulate on the ‘cautionary principle,’ which is that if you don’t know the risk, you don’t allow it,” says Darrington, a Brookings area native who started his career immediately after earning his veterinary science degree at Iowa State University in Ames.
“Is there a risk? Sure,” Darrington says. “Can we define the risk? Not really.”
The study looks past the precautionary principle to discover the differential risk in winter applications, compared with the use of conventional fertilizer.
“How can we manage that and understand it better?” Darrington says. The issue is especially concerning for CAFOs wanting to haul “dirty snow,” perhaps cleaning their concrete feedlot aprons in winter.
“They might have to stockpile manure for the winter and not be able to apply it,” Darrington says. “Our research is asking the question, ‘What is the effect of applying it during the winter on runoff quantity and quality,’” Darrington says. “A lot of this stuff is going to move with soil, too. Does manure lose more nutrients to surface runoff versus conventional fertilizer?”
That’s one of the issues.
Three watersheds
The study on Schmidt’s land is located at an unusual site - an intersection of three watersheds near Colman, S.D., with an 8 percent topographic slope to the land.
“It’s a little unique to have three different watersheds right next to each other,” Darrington says. “The particular site has a north, south and east watershed, all on the same slope. The third watershed is partially terraced, so it divides where the water goes. The site was chosen because it is easy to verify the weather impacts, which are the same.”
The researchers are working with three, 5- to 8-acre fields. Each is divided in half, based on area.
On the east side control, there is only winter-applied conventional fertilizer used - no manure application.
“We gather the runoff from that site, monitor how much there is, and then do water sampling to see what the actual concentrations are - calculate out the nutrient loss,” Darrington says.
On the north watershed in the study, they apply manure only to the lower 50 percent of the topography and apply conventional fertilizer on the upper 50 percent and monitor levels. Soil tests and manure tests dictate the application rate. The rate was 4 to 5 tons per acre in 2015, compared with 17 tons per acre in past years, says Mike Schmidt, the landowner cooperator in the study. The manure rate is dictated by the soil tests, manure test and the desired crop performance. They aim for 160-bushel corn and 45-bushel beans.
On the south watershed they apply manure to the top 50 percent of the topography and conventional fertilizer to the lower 50 percent, and then monitor.
The researchers then see what the differences are in the water quality results. The study collects data on ammonium nitrate, dissolved phosphorus and suspended solids, measured in parts per million or milligrams per liter. The study has been slow because of a lack of snowfall in the past few years.
“We don’t have many data points yet, so there is not enough for a solid recommendation,” Darrington says.
Fickle weather
If the study finds significant differences between manured or nonmanured land, the current recommendations would be confirmed. If not, the regulations could be adjusted accordingly.
“It comes back to what are the best management practices for applying manure and how can that relate to the winter application,” Darrington says. “Right now, we don’t really know what the best way is. Historically, it’s been just don’t do it and that avoids the risk. What we’re trying to establish is what the risk actually is.”
Ongoing studies would further impact the actual limits.
For slopes of zero to 4 percent, for example, there might be a need only for a limited buffer zone for manure application in winter, or anytime, he says. In cases where land is largely flat, the presence of draws, or waterways, might still create an unacceptable risk.
Darrington says the rate of volatilization is pretty well understood. “You end up giving up, potentially, 70 percent of the (nitrogen) if it’s flat on the surface, which is why the best management practices are to knife it in or to apply it on the surface or till it in within 24 hours in the fall to avoid that volatilization. It depends on temperature fluctuations throughout the winter. If it stays frozen, it won’t volatilize as much.”
He adds, “We’re going to plan to do at least two or three more years.”
The more data, the more reliable the data. The site this year was prepared on Feb. 17, checking the three flumes to provide flow data, using a laser level to determine water rate and flow rate. When the system records an inch of water depth in the flume, an automatic sampler can take a series of up to 24 water samples, collected every two minutes.
Across the border
Pete Bakken lives in Rock County, Minn., but also farms in South Dakota. His Blac-X Farms is the subject of a similar study through the Discovery Farms Minnesota program.
The Bakken farm is a CAFO, so it keeps track of all of it’s manure and works with Extended Ag Services of Lester, Iowa, and Lakefield, Minn.
“To me, the rules and regulations and accompanying paperwork is time consuming,” Bakken says.
Minnesota farmers are allowed to winter-spread manure, but that’s limited on a per-ton, per-acre amount. Bakken thinks spreading manure in the wintertime is a “good concern to probably have,” but if farmers must stockpile it, spreading it in the springtime isn’t a good option because of soil compaction.
George Rehm, a professor emeritus of the University of Minnesota in St. Paul, is the coordinator of the Discovery Farms Minnesota project, which gets financing from state corn and soybean groups and collects data on 11 farms in the state, including Pete Bakken’s Blac-X Farms in Garretson, S.D.
“The whole purpose is to monitor and measure sediment, nitrogen and phosphorus,” Rehm says. “I have an aversion to manure applied on the surface in the wintertime. I think that’s not the best practice farmers can use, but I understand that if the manure pit fills up and they have a huge pile, and they have an opportunity to spread it, they’ll spread it.”
The right thing
Rehm says Bakken is making an effort to do the right thing with manure handling, and the nutrient losses of sediment, nitrogen and phosphorus they’re seeing on Discovery Farms are “much less than perceived by the public.”
Jodi DeJong-Hughes, a University of Minnesota Extension Service educator in crops and soils, based in Willmar, Minn., says winter application of manure is not the best for either the environment or economics of the farm, because it wastes nutrients that otherwise would be available to plants.
“I think we already know the answer,” DeJong-Hughes says. “When manure is placed on snow and the snow melts, the water can take away the nutrients. There’s so many great things in manure - a lot of carbon and a lot of micronutrients. It’s one of the best things to put on your soil.”
Bakken, who has a cow-calf operation and feedlot, participated in South Dakota’s Adopt-A-Farmer program and is a subject of a popular YouTube video that was posted to help his daughter’s fourth grade class understand his work handling manure. He doesn’t think spreading manure in the winter needs to be a detriment. But he says he signed up for Minnesota Discovery Farms because he wants to know the impacts of what he’s doing, rather than have people tell him they think he’s harming the environment.
“I’m trying to prove that either I am or I’m not,” he says. “If we’re going to be regulated, I would prefer being regulated to an application that’s reasonable than no winter spreading at all.”

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