As the general public outcries against applying manure products via irrigation methods grew louder, a unique work group formed to review related issues, discuss the technical details and develop guidance on the practice that is also growing in interest among dairy producers.
Following 16 meetings, held between July 2013 and September 2015, the work group released a written report in April titled “Considerations for the Use of Manure Irrigation Practices.”
A webinar presented on April 14 outlined the benefits and concerns analyzed by the group and highlighted parts of the report that may have an impact in forming policy.
Dr. Ken Genskow, associate professor in the Department of Urban and Regional Planning and extension specialist, University of Wisconsin – Madison, was a member of the work group, which included two others from the university, the USDA, Wisconsin state department representatives, county health agents, dairy farmers, an agronomist, a nutrient applicator, a concerned citizen and the state land and water association.
“Our intended audience includes state and local agencies, interested stakeholders and producers interested in considering these practices,” Genskow said.
Dr. Becky Larson, assistant professor in the Department of Biological Systems Engineering and extension specialist, University of Wisconsin – Madison, who also participated in the work group, said the group looked at the benefits of irrigation, as well as the concerns, which were primarily related to human health and the environment.
Irrigating manure was found to be beneficial because it increases the window for manure application. “The window for manure application is narrowing,” Larson said, noting land application should be avoided during winter, when the ground is thawing and when there is precipitation. Irrigation increases application timing to the summer months while the crop is growing.
Since it can be applied to a growing crop, the utilization of nutrients in the manure will be greater than applications to the soil itself.
Also, the installation of a permanent irrigation system and pipeline to the field can potentially reduce the amount of tanker traffic on public roadways.
The concerns were broken into five distinct areas: drift, odor, water quality, air quality and pathogens.
1. Drift
Drift is the aerial movement of liquid outside the intended application area. “Drift is very different than overspray, which is spraying outside the bounds of the field,” Larson said, noting the group did agree that overspray should not be recommended.
They found that practices to reduce drift include maximizing the droplet size, minimizing release height, minimizing wind speeds and using barriers, like tree lines to prevent any drift from impacting other fields or neighbors.
2. Odor
“Odor is one of the biggest concerns – next to pathogens – from citizens,” Larson said. “However, odor perception is variable. It is difficult to say how people are going to respond to odor.”
Unfortunately, because of the way manure irrigation systems are designed, they will generally have an increase in odor compared with other manure application systems. There are some techniques to mitigate odor, such as siting, dispersion (winds greater than 5 mph), edge-of-field barriers, manure processing techniques and large droplet size.
3. Water quality
Concerns for water quality pertained to both runoff and groundwater. However, the effect on water quality from application via irrigation wasn’t much different when compared with other land application methods, and dairy operators should follow all of the standards that exist regardless of how manure is applied.
Plus, the ability to apply diluted manure in smaller portions throughout the growing season results in manure reaching a more shallow depth into soils, which could reduce the amount of runoff or groundwater penetration.
4. Air quality
Concern for air quality was grouped into three categories: particulate matter, greenhouse gas emissions and hazardous pollutants (including ammonia and hydrogen sulfide).
“On a farmstead, particularly near manure storages, hydrogen sulfide concentrations can be at dangerous levels,” Larson said, “but in the field, regardless of application practices, we have not measured hydrogen sulfide concentration levels that would reach a level of concern to human health.”
The same mitigation techniques as mentioned earlier – edge-of-field barriers, larger droplet size and low release height – could be used to address air quality.
5. Pathogens
While the work group was meeting, a concurrent study was being conducted to look at microbial risk in terms of setback distances from the irrigation of dairy manure. Click here for more information on the findings of this study.
Genskow said the work group developed a list of baseline recommendations that reached a consensus within the group. In all cases of manure irrigation, the group recommends producers and applicators do the following:
- Follow all existing laws for animal waste and nutrient management
- Have and follow a 590-standard nutrient management plan
- Take appropriate steps to minimize drift
- Ensure no overspray of irrigated manure
- Have suitable means of supervising and controlling equipment
- Have suitable means of determining relevant weather information
- Have means of preventing backflow if connected to a groundwater type system
- Ensure no human waste or septage is processed with manure at any part
- Determine wind speed as 15-minute mean measured at field level
- Have drop nozzles if center pivot is used
- Set nozzles and pressures for “coarse” or larger droplet sizes
- Have no more than eight irrigated applications to any single field per season (with potential for more depending on the level of advance treatment of manure prior to irrigation)
In terms of the appropriate amount of setback (the minimum distance from the wetted perimeter where manure is applied), the group was unable to reach a full consensus in all areas. Here is the level to which they could agree:
- Setback for road right-of-way: 0 feet for all types of roads and highways (near consensus)
- Public forests with no recreational access: 0 feet (consensus)
- Private forests: 0 feet (near consensus)
- Adjacent ag properties: 0 feet for pasture and crops that are not organic or raw consumed (near consensus); 0 to 50 feet regardless of crop (close-to-near consensus)
- Dwelling: 500 to 750 feet under various conditions for wind speed and direction (near consensus); 250 feet for some situations (close-to-near consensus and no agreement for others)
- Property line for public recreation area, school or playground: 100 feet if wind speed is less than or equal to 10 mph and the wind is parallel or away from the building or property line (near consensus); other distances (no agreement)
For nighttime manure irrigation application, the group came to a consensus not to recommend this for raw or untreated manure. They reached near consensus that it would be the same as daylight if the manure is treated, the wind speed is greater than or equal to 2 mph but less than or equal to 10 mph, and the wind is parallel or away from buildings or the property line.
Upon releasing the report, the work group addressed questions pertaining to it and plans to make this information available for public and private entities to use when addressing concerns related to the irrigation of manure. PD
For further details on these and other recommendations, download the full report here (PDF, 2MB).
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Karen Lee
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PHOTO: Staff photo.
