Scientists: Manure irrigation gets bad rap; health risks low

Manure irrigation is the application of livestock manure or process wastewater through irrigation equipment. One method is center-pivot in which farmers use a large sprinkler that rotates to precisely apply the liquid on crops. Often, drop hoses are used to sprinkle the water from a few feet off the ground. An “end gun” on the end of the sprinkler sprays the liquid to the edge of the field.

The researchers went to three farms in different parts of the state and measured the amount of pathogens in the air at various distances from an active manure irrigator during various weather conditions.

The conclusion: The risk of getting sick is extremely low.

“There are no benchmarks for the presence of pathogens in spray irrigation so we had to relate it to other areas, such as disease caused by pathogens in swimming water or drinking water. The recreational benchmarks were higher than what you would see with manure irrigation,” Tucker said.

As an example, health guidelines define a safe swimming area as the chance of as many as 32 out of 1,000 people contracting an acute gastrointestinal illness from the water on a single day. In comparison, the researchers found that during manure irrigation there is a 3-in-100,000 chance of getting sick from airborne pathogens while 100 feet away and a 3-in-1 million chance when 1,000 feet away.

“With manure irrigation, there is a lot you can do to minimize risk, such as using a setback distance, limit the number of applications per field and only do it during low wind speeds,” Burch said.

Larson said she realizes that manure irrigation has an image issue, but it has many benefits compared to traditional manure use.

“With manure irrigation, you apply less manure overall to the fields, which benefits water quality,” she said. “You can be more exacting where you want it and you can do it at different times of the year — not just wait until the fields are clear.”

Farmers would also be less likely to use chemical fertilizers if they could use manure as a plant nutrient throughout the year.

Another benefit is that manure irrigation gets trucks off the road — something favorable to municipal officials. The heavy trucks that carry manure from the farm to the fields can add wear and tear to roadways over time.

The workgroup on manure irrigation made recommendations to help local officials as they make decisions regarding irrigation rules:

Ask farmers to minimize drift, over spraying and supervise equipment
Ask farmers to limit irrigation on windy days
If the irrigation system is connected to water, make sure there is backflow prevention in place
Do not use septic waste
Using drop nozzles helps minimize drift

SEE THE RESEARCH ONLINE: To see the scientific findings, video presentations and other information, go to http://fyi.uwex.edu/manureirrigation.

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