URBANA, Ill. — Because of their non-point source nature, most farms aren’t regulated under the federal Clean Water Act. That leaves pollution control up to the states, resulting in a patchwork of approaches that are difficult to evaluate.

A new study by the University of Illinois focuses on local manure management regulations in Wisconsin and how they affect water quality in the state.

“Wisconsin is unique because it has allowed counties to participate in enforcement of state agricultural code without state approval,” Marin Skidmore, an assistant professor in the Department of Agricultural and Consumer Economics, and lead author of the study, said in a news release.

Skidmore and her co-authors conducted interviews and compiled documents on manure-management ordinances in Wisconsin counties from 2008 to 2020. To evaluate water quality, they recorded average monthly data for ammonia and phosphorous concentrations in water bodies obtained from the Water Quality Portal, a database of U.S. information.

“We find encouraging evidence for the effectiveness of local enforcement of management regulations,” Skidmore said. “Two aspects of local ordinances are particularly effective, leading to reductions in nutrient concentrations between one and three years. Both aspects align with the four Rs of nutrient management — applying the right source at the right rate, right time and right place.”

The first of those rules requires all farms to develop a nutrient-management plan, regardless of whether they have a manure-storage facility. The second rule addresses a subset of counties that have more restrictive rules on manure spreading based on the presence of Silurian bedrock, also requiring a nutrient-management plan.

“In a nutrient management plan, farmers must outline how, when, where and at what rate they’ll apply nutrients,” Skidmore said.

To develop a nutrient-management plan farmers must first have their soil tested, then test or estimate the nitrogen and phosphorus content in the manure. Then they must determine fertilizer needs based on crops, acreage and soil conditions. County agencies work with farmers to offer training and support, as well as grants to offset costs of developing a plan.

“Our study shows that some easily implemented regulations can have a positive impact on water quality,” she said. “We also show that local agencies are a valuable resource for regulation enforcement. Counties are able to address problems before they escalate and can provide a quicker response. They have staff who are living and working in the communities so they may have a different awareness than state organizations.”