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Runoff filled with excess nutrients from cropland in Midwest states is a well-documented problem. For a very long time, it has contributed to the contamination of local waterways and drinking water and to the dead zone in the Gulf of Mexico, which researchers anticipate will cover 6,700 miles this year, an area the size of Connecticut and Delaware combined.

Why Minnesota?

EWG recently moved its offices to Minnesota, so the organization has been turning its focus on its new backyard in various reports. Porter also said the Minnesota Department of Natural Resources (DNR) does a particularly good job tracking CAFOs, which gave the team access to quality data as they developed the research model.

And Minnesota’s farm landscape has changed in a way that is typical of agricultural states across the country, especially in the Midwest. Barb Sogn-Frank is a policy program organizer for the Land Stewardship Project, a Minnesota-based organization that has been advocating for small farms since the 1980s farm crisis. She said slowing the expansion of CAFOs is now one of the group’s top priorities.

“We work on many things,” she said, but when it comes to supporting resilient rural communities and independent family farmers, “one of the biggest threats is industrial-scale animal confinements.”

According to data from the DNR, the number of CAFOs in the state has tripled since 1991. Most of the growth has been in hog CAFO construction in the south of the state.

According to a recent Food & Water Watch report, Martin County in Minnesota now ranks ninth in terms of county hog CAFO concentration across the country and produces hog waste equivalent to the human waste produced by the residents of Austin, Texas.

Minnesota’s concentrated hog production spills over its Southern and Southeastern borders into surrounding states. Iowa (also home to the most egg-laying hens raised in CAFOs), South Dakota, Nebraska, and Illinois all have high levels of hog CAFO concentration, as does North Carolina. Dairy CAFOs are concentrated in Michigan and California, while Nebraska, Texas, and Kansas are home to many of the largest feedlots for beef cattle.

The Research Methods

First, some background: When a farmer or company builds a CAFO, the process generally involves calculating how much waste the animals will produce and identifying local cropland that needs fertilizer as a means of disposing of the waste. The manure accumulates on-site and is then trucked to nearby fields to be applied, by spraying or injecting (sometimes called knifing). Manure can be an effective, nutrient-rich fertilizer, and is touted as a substitute for chemical fertilizer. But issues with the system arise because the concentration of animals means they’re constantly producing waste and the manure has to go somewhere. If it’s more than the cropland can handle, farmers may apply it anyway.

To conduct the research, the team used “geospatial analysis,” which essentially layers different spatial data sets together. They used DNR data on CAFO locations and then wrote a program that allocated the amount of manure that would be produced at those CAFOs to available cropland nearby, Porter explained.

While the data is not based on actual applications on individual fields, Porter said that there is reliable information that shows manure from CAFOs typically ends up within a certain radius, given how heavy and expensive it is to transport. “We’re pretty confident that we’re getting a good regional perspective,” she said.

They then layered on data on where commercial fertilizer was being applied, which came with more significant limitations. The state tracks fertilizer sales at the county level, so they took those sales and then allocated the fertilizer based on cropland needs by region. Of course, it’s impossible to know exactly how much of and exactly where the fertilizer sold was applied.

Manure Mapping

Still, based on the analysis, the report identified 13 counties where nitrogen from manure and fertilizer likely exceeded the recommendations of the Minnesota Pollution Control Agency by more than half. The data showed that Martin County, where hog production is most concentrated, was the most saturated, with an estimated 14,368 tons of nitrogen overload.

“We found several areas in Minnesota that are essentially fully saturated with manure,” Porter said. “We didn’t find many areas where if you had access to every field, there was too much, but we found areas where you pretty much needed every field around those feedlots to dispose of the manure.”

Agricultural experts would likely assume that in areas producing enough or too much manure for surrounding fields, commercial fertilizer sales would be lower, since farmers would presumably need less to meet their crops’ nutrient needs. Surprisingly, the data did not show that correlation. In many cases, fertilizer sales were in excess of recommendations for surrounding cropland even in areas producing excess manure.

Porter said that could be because farmers are unsure of the amount of nitrogen and phosphorus in the manure. She also pointed to the fact that while nitrogen in runoff is talked about often, phosphorus is often ignored but is an especially important issue in areas where manure is applied for its nitrogen content. In the teams’ simulation, they found an excess of more than 10 pounds of phosphorus per acre on close to 1.5 million acres.



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