Manure Irrigation report addresses information deficit

Colleen Kottke Associate Editor
Now Media Group


Today more and more farms are turning to the practice of spraying liquified manure over fields using irrigation equipment.

Although not currently in widespread use in the state, University of Wisconsin Extension officials say the practice is expected to grow over time. And as this practice grows, so do the concerns and questions among residents living near those farm fields.

While the application of liquid dairy manure by traveling gun or center pivot irrigation systems offers several potential

benefits: reduced road impacts from hauling, optimal timing for crop nutrient uptake, and reduced risks of manure runoff and groundwater contamination, irrigation could also increase the risk of airborne pathogen transmission from

manure to humans and livestock compared to other application methods

These concerns have many local governments — especially those with a large number of CAFOs residing in their municipality — looking for more information and data to help guide their decisions on whether to regulate or even ban the practice.

The Wisconsin Manure Irrigation Workgroup, a UW-Madison/UW-Extension-led group tasked with assessing the potential pros and cons associated with manure irrigation, released its final report on April 14 following a webinar presentation about the report's findings. The report and the webinar are available for viewing online at http://fyi.uwex.edu/manureirrigation/

Manure irrigation workgroup member and UW-Madison Urban Planning Professor Ken Genskow said there is increasing debate about the pros and cons of this practice.

'Many communities are struggling to make decisions about if and how manure irrigation can work for them — often due to a lack of information,' Genskow said. 'This report provides some form of guidance fo stakeholders and gives a broad overview. It this point its just informational, we're not setting policy. Our mission was to review the information available and compile it into a document to help citizens and local governments decide their futures.'

Information deficit

To help address this information deficit, in 2013, the Wisconsin Department of Agriculture, Trade and Consumer Protection and the Wisconsin Department of Natural Resources requested UW-Madison/UW-Extension convene a workgroup to study the issue. The workgroup, composed of scientists, public health specialists, state agency experts, farmers, conservationists and others, spent over two years gathering and reviewing scientific information on the practice and developing their report, which includes findings, responses and recommendations.

Recognizing that any future public policy would originate at the state and local levels, the group aimed to gather critical information and put it in the hands of the people who need it most.

Early on, the workgroup gathered citizen input to help guide its efforts, hosting public symposiums on the topic — which included opportunities for public comment — in Stevens Point and Menasha. Workgroup meetings were open to the public, and workgroup members accepted comments throughout the process.

'The input helped set the agenda for our group discussions,' says Genskow.

Assessing concerns

Workgroup member and report co-editor, Becky Larson, UW-Madison assistant professor of biological systems engineering and UW-Extension biological waste specialist, said both the public and producers were interested in understanding more about the concerns related to human health and the environment, benefits and uses of the manure irrigation as well as looking at best practices in helping to reduce the environmental impacts and operational issues.

The workgroup assessed concerns associated with manure irrigation, including droplet drift, odor, water quality, air quality and airborne pathogens. They also explored potential benefits related to the timing of manure applications, road safety and reduced road damage, and other farm management and economic benefits.

'Things we wanted to look at was the potential impact on surface waters, organic crops, homes, waterways, and what kinds of practices could be used to reduce drift,' Larson said. 'Key things included maximizing droplet size so manure falls to earth faster, lowering the release height, minimizing wind speed, and using barriers to prevent any drift so there isn't an impact on the next field or neighbors.'

Human Health Risk

To understand the human health risks associated with manure irrigation, researchers need to understand how long pathogens survive after being sprayed into the air. A lack of field studies of the practice led the USDA Agricultural Research Service to conduct a study in tandem with — but independently from — the workgroup's efforts.

The results of that project are shared at the end of the report, in a section titled 'Airborne Pathogens from Dairy Manure Aerial Irrigation and the Human Health Risk.'

'This USDA-ARS study was the first in-the-field research project to measure pathogens and other microbes being spread through the air in this way and to then calculate a risk. The research found that risk of acute gastrointestinal illness from pathogens reduces with increased distance,' Larson said.

The study, however, does have its limitations as far as addressing respiratory illnesses. In addition, there are still emerging areas of science yet to be fully understood, including the presence of hormones in manure, said Mark Borchardt, USDA-ARS, research microbiologist.

'We put a lot of work into this study and did the best that we could. But no study is perfect — all studies have limitations,' Borchardt said. 'Concerning this study, we can't classify what is safe or unsafe; just what the acceptable risk level is. That's not for the scientists to say but rather for the policy makers to do.'

According to the report concerning pathogen contamination, a person located 500 feet or further from a manure spray source would incur risk equivalent to what's acceptable under federal drinking-water regulations.


It's important to note that the workgroup did not reach consensus on every issue concerning manure irrigation including setback distances from various land uses and property types.

The group did, however, reach a consensus regarding manure irrigation practices that include following all existing relevant state and local laws regarding animal waste and nutrient management; have and follow a NRCS CPS 590 Nutrient Management Plan (NMP); take appropriate steps to minimize drift; ensure no overspray of irrigated manure; have suitable means of supervising/controlling the equipment (e.g., active supervision, automatic sensors/controls, etc.); have suitable means of determining relevant weather information (to include: wind speed, wind direction, and temperature); have means of preventing contaminated backflow if equipment is connected to water sources and ensure that no human waste or septage is added to (or processed with) the manure.

Additional recommendations include: wind-speed will be determined as a 15-minute mean measurement on the field; drop nozzles on the center pivot; nozzles and operating pressures selected to provide 'coarse' or larger droplet sizes; apply all materials and abide by all setbacks in accordance with an approved NRCS CPS 590 NMP 74; and no more than 8 irrigation applications to any given field per growing season (potential to increase if manure is treated using accepted pathogen reduction technologies).

Controversial topic

The final chapter of the report includes responses to potential benefits and concerns, and, taking all of these factors into consideration, it offers science-based recommendations for reducing risks from manure irrigation.

'We recognize that there's controversy around this subject and we really genuinely tried to put as much science-based information in the report and reflect every opinion,' Larson said. 'We know that people have strong feelings about this. We hope that they read the report with an open mind and use this information to make decisions supported in science.'

Genskow hopes that stakeholders will find the report a useful resource to help guide them with future decisions that may include establishing safe setback distances from irrigated dairy manure.

'We really want to reach local officials and others interested in the issue, so they are aware of this resource and they know where to look for more information,' Genskow said.

In order to give people a chance to read and discuss the full 80-plus-page report and then ask questions, a follow-up webinar will be held during the week of May 16.

To Learn More

To listen to the April 14 webinar or read the report on manure irrigation practices, visit http://fyi.uwex.edu/manureirrigation/