Iowa Agriculture Runs on 110 Billion Pounds of Manure, at a Cost to Its Water

During planting season in Iowa, Landon Plagge’s fields reek. Sour and earthy, almost like rotten eggs and fermenting hay, the scent repels the unacquainted nose. But Plagge is unbothered.

“I’m used to it,” he said, laughing. “I’m immersed in shit, I guess.”

In addition to the soy, corn, oats and rye he grows on his family farm in northern Iowa, Plagge operates a 10,000-head confined hog feeding facility, one of more than 4,000 large concentrated animal feeding operations in the state. Those hogs, he said, produce 3 million gallons of liquid manure each year.

He puts that waste to use, spreading it across his fields to act as fertilizer—and buying chicken, cattle and hog manure from nearby livestock facilities so his 4,000 acres of farmland have enough nutrients. 

Manure “gets a bad rap,” said Plagge, a proponent of practices boosting long-term soil health and reducing runoff. While livestock confinements and feedlots are accused of polluting Iowa’s environment, the manure itself is not the problem, he said. “It’s the crop production that is the issue.” 

Iowa is the nation’s leading producer of pork and corn (some of which goes toward feeding livestock), and its agriculture industry both generates and uses copious amounts of manure—over 100 billion pounds each year. With nitrogen, phosphorus and other micronutrients critical to plant growth, the livestock byproduct makes for a cheap and effective fertilizer. 

But the economic pressure faced by farmers, time constraints on when manure can be spread and the difficulty of knowing its exact nutrient contents all lead to overapplication in the fields, experts say. Nitrate and phosphorus from excess manure leach into waterways. That’s created a long-running clean-water crisis in the state. 

According to Iowa’s Impaired Waters List, 722 waterway segments in the state, half of all those tested, do not meet water quality standards for public water supplies, recreational use or wildlife protection. And most of the rest show signs of potential problems. 

Many of these impairments are due to phosphorus-fueled algae and bacteria blooms or dangerously high nitrate levels. Studies link long-term exposure to nitrate in drinking water, even at low levels, to various cancers as well as birth defects.

In Iowa, the only state in the nation with rising cancer rates, such water pollution is costly. When nitrate levels spike in the nearby Racoon and Des Moines rivers, Des Moines Water Works spends about $10,000 a day operating its nitrate removal facility. 

Half-hearted mitigation attempts by the state, which is hesitant to place strict regulations on farmers, have done little to address the issue. The volume of ag pollutants leaving Iowa and entering major waterways has risen steadily over the last two decades.

While manure fertilizer offers the promise of healthier soil and a continuous cycling of nutrients in and out of the environment, the reality is a leaky cycle that feeds Iowa’s crops while polluting its waterways. 

More Factory Farming, More Manure

Between livestock and crops, Iowa is the largest producer of agricultural goods in the United States after California, with a market value of over $44 billion. The state is home to 3 million human residents and 25 million hogs, according to the U.S. Department of Agriculture, plus 46 million chickens and 3.5 million cattle.

Iowa feeds America, but that food comes with a whole lot of manure. Livestock in the state’s concentrated feeding operations produce 110 billion pounds of manure each year, according to Food & Water Watch’s analysis of the 2022 USDA Census of Agriculture. That’s 25 times the waste produced by the state’s human residents, the group said.

Where does all that manure go? Straight back into Iowa agriculture in the form of fertilizer in almost every case, said Daniel “Dr. Manure” Andersen, an Iowa State University researcher who specializes in manure management and water quality. 

All the manure produced in Iowa could provide enough nitrogen and phosphorus for less than a third of the state’s crops, said Andersen. “I’m not saying we need more livestock, but we have the capacity to use the manure that we do generate, and I think that’s a blessing.”

Manure is typically more cheaply available to farmers than synthetic fertilizers, and its organic matter and micronutrient contents build soil microbial diversity and improve soil structure over time. In Iowa, it can also be sourced hyper-locally. Liquid manure in the state rarely travels more than three miles from its original livestock facility, said Andersen.

But this locally contained system of manure production and use is changing as concentrated animal feeding operations, sometimes called factory farms, grow larger and larger, said Amanda Starbuck, research director for Food & Water Watch and co-author of the organization’s analysis of Iowa manure production. 

The average Iowa hog farm is selling 24 times more animals than in 1982, according to USDA data. Yet in the same time period, the state lost nearly 90 percent of those farms. The consolidation of the livestock industry has consequences for manure management, said Starbuck.

“In ages past, it was more common to have more of an integrated system,” Starbuck said, in which a farmer would use manure from their own livestock to fertilize their own crops. “If all is done well, you can have kind of a closed loop sort of system. But that doesn’t necessarily happen on these big-scale farms,” she said.

For Plagge, who uses manure from his hogs and nearby livestock facilities for 95 percent of his farm’s fertilizer needs, it’s a key part of regenerative agricultural practices. 

“We can spend half as much and have better soil fertility, better soil health,” he said. “It’s just good stuff.” 

But Plagge uses less fertilizer than most. His farm’s adoption of cover crops, a three-crop rotation and no-till practices have enriched soil health, he said, lessening his dependence on fertilizers. 

“We can use less nutrients,” said Plagge, while farmers using traditional tillage and more intensive soil management practices are more reliant on adding natural or synthetic nutrient sources to their fields. 

There’s a fine line between fueling plant growth and over-fertilizing, accelerating nutrient runoff and pollution. With manure fertilizer, it can be trickier to strike that balance, said Andersen, the manure management researcher.

Whereas farmers can tailor the exact nutrient contents of synthetic fertilizer, manure is less predictable. The nutrient contents of manure can vary widely by livestock species, diet and even within a single livestock facility, said Andersen. 

Manure typically also has a lower nitrogen content than synthetic fertilizers, he said. “So historically, with manure, we’ve tended to over-apply phosphorus to get enough nitrogen to support crop production.” 

Phosphorus not taken up by crops enters waterways via soil erosion and stormwater runoff, fueling algal blooms and reducing oxygen available to other organisms. Meanwhile, extra nitrate dissolves in water, leaching out of fields as runoff and via man-made drainage systems meant to control soil moisture.

Failing to Keep Pace

The consequences of this pollution are felt near and far. 

The Des Moines metro area, home to nearly a quarter of Iowa’s population, has faced water use restrictions since June due to dangerously high levels of nitrate in drinking water sources. The regional water utility announced it will gradually loosen those restrictions beginning this week, while continuing to monitor nitrate levels. Meanwhile, the state is one of the leading contributors to nitrate and phosphorus buildup in the Gulf of Mexico, creating a low-oxygen marine “dead zone” each summer. 

In 2014, Iowa rolled out its Nutrient Reduction Strategy to try to address the problem. The strategy promotes voluntary conservation measures for farmers looking to minimize nutrient loss from their fields. But using the carrot instead of the stick has done little to stem the flow, a common issue across the country. 

Iowa’s Department of Natural Resources, which handles environmental protection in the state, remains committed to its Nutrient Reduction Strategy, said Tammie Krausman, the agency’s public information officer. 

“While nitrate levels remain a serious concern in some waterways, the strategy was never intended to deliver short-term results. It represents a long-term, incremental approach to change that depends on widespread adoption of conservation practices across diverse landscapes,” Krausman wrote in a statement.

A decade since the strategy’s inception, however, the volume of nutrients leaving Iowa has doubled, said Larry Weber, director of the University of Iowa hydroscience and engineering program, where he manages a statewide network of water quality sensors.

“In the environmental and water quality space, we are not keeping up with the pace of the intensification of agriculture,” he said. 

Even as fertilizer and manure use grow, further efforts to control nutrient loss have met swift resistance from the Iowa Legislature and governor, Weber said.

In 2023, the Legislature passed a budget bill slashing funding for the Nutrient Research Center at Iowa State University, which bankrolls the network of 90 water quality sensors. The network, among the nation’s largest continuous water-quality monitoring systems, now relies on grant funding from the Walton Family Foundation, which will expire in 2026. 

State Sen. Dan Zumbach, a Republican who sponsored the budget bill, did not respond to requests for comment. Republican Gov. Kim Reynolds, who signed that bill into law, also did not respond to requests for comment.

“At the state level, things are dominated by the agricultural industry. Anything that puts restrictions on agriculture gets pushed back pretty quickly,” Weber said.

An Inexact Science With Little Oversight

Absent statewide restrictions, manure management decisions are left largely to individual farmers.

Those with operations of more than 500 cattle or 1,250 hogs must submit a manure management plan to the state Department of Natural Resources, detailing how they plan to distribute their manure.

Based on state guidelines for nutrient levels in fields, farmers calculate how much nitrogen and phosphorus can be added to the soil and thus how much manure to apply. These calculations are often based on estimates of both soil nutrient contents and manure nutrient contents, Andersen said. 

Farmers submitting manure management plans are required to test their soil phosphorus levels every five years, but there aren’t currently great tests for nitrogen availability, Andersen said. Not all nitrogen in the soil is in a mineral state available for plant uptake, and temperature, oxygen supply and rainfall can affect how much nitrogen will be available in the coming growing season. 

“For a farmer looking to get it down to a science, it’s challenging,” Andersen said.

That exacerbates overapplication. Farmers seeking to maximize yield and profits will err on the side of more manure, perhaps avoiding a larger economic cost but creating an environmental one, Andersen said. 

“Overapplying doesn’t have any visual cues. The crop you’re growing will look great, but it has water-quality concerns long term,” he said.

Timing challenges with manure application worsen nutrient loss, both Andersen and Plagge said. Most farmers opt to spread manure in the fall immediately after the harvest and before the ground freezes, but the longer manure sits on a field before the next year’s planting, the greater the risk of nitrate leaching into waterways.

Plagge applies manure in both the spring and fall. But in the fall, he only adds manure to fields planted with cover crops. While these crops grow, they soak up the nutrients and then die during the winter. Come spring, the decomposing plants release the nutrients for the newly planted crops to use, he explained.

Applying manure to cover crops is a good way to reduce nutrient loss, Andersen agreed. The practice is rare, but growing. 

“Only about 5 to 10 percent of [Iowa’s] acres are planted with cover crops, but that’s still a huge increase from 10 years ago,” he said.

Andersen has also witnessed more “edge of field” practices that can reduce nutrient runoff, such as nitrate-capturing bioreactors and buffers that filter water drainage through nitrate-thirsty plants. These practices have been criticized for their ineffectiveness, however, and may address only a minor portion of the state’s nitrate load.

Andersen is particularly interested in mitigating manure nutrient loss at the source: honing the nutrient level tests and calculations available to farmers for better decisions about how much to apply. 

“It’s a circular system, but it is still a leaky system, and a lot of that is cropping choices that you make,” Andersen said. “I think we’re all trying to figure out how we can do better at reducing some of those leaks.”

A fix is unlikely to come from the current state government, believes Weber, the scientist monitoring water quality statewide. The governor, responding to protestors July 10 demanding action on agricultural pollution, said regulation is “not the answer” to the state’s water quality crisis and reiterated the value of voluntary conservation efforts.

“It’s a stick-the-head-in-the-sand approach,” Weber said. “If the only resources that we want to optimize are our agricultural and economic resources, then it’s going to come at a cost to our natural water and human resources.”