It's a stinky distinction, but Iowa leads the nation when it comes to the amount of poop its people and livestock generate, research from a University of Iowa scientist shows.

Christopher Jones, a UI research engineer, calculated that Iowa's population — based on the waste from the state's 3.2 million people and nearly 110 million chickens, pigs, turkeys and cattle — would be the equivalent of 168 million people.

It's about as many people as in Bangladesh, a country in south Asia with 165 million people.

Factor in land size, and Iowa ranks first in the nation for waste creation, Jones writes in a blog he's titled, "50 Shades of Brown."

"Just to ensure clarity, in Iowa, we are generating as much fecal waste in every square mile as 2,979 people," Jones writes. "For reference, Iowa City is the second-most densely-populated city in Iowa and has 2,775 people per square mile.

"So imagine an Iowa-sized Iowa City," he wrote.

The pig manure generated in Iowa "floats our state to the top," writes Jones, a scientist at IIHR-Hydroscience & Engineering, the UI's first hydraulics lab.

"Iowa is home to one out of every three U.S. hogs, with 23 million residing here at any given moment," a population that's increased 64% since 2002, he writes.

After Iowa, the top poop-producing states are Delaware, Wisconsin, Nebraska and Pennsylvania, based on waste created per square mile. Delaware has 52 million chickens.

It's the second blog Jones has written about the massive scale of waste from Iowa's livestock population.

The first — "Iowa’s Real Population" — showed by watershed the equivalent human population, based on human and animal waste. It showed that northwest Iowa watersheds, for example, produce the waste equivalents of Bangkok, London and New York City.

Jones wrote the second blog after readers asked him to compare Iowa's waste to other states'. He also updated the state's livestock population.

His interest in livestock waste stems from his research of changes in Iowa's water quality — and what has an impact on its rivers, streams and lakes.

He wants more candid discussion about the environmental challenges Iowa faces.

Most Iowans know the state has a large livestock population, but Jones wanted to assess the industry's waste impact after he and other researches published a study last year that found two western Iowa watersheds, with some of the state's largest pig and cattle concentrations, had double the average nitrate levels of seven other watersheds in the region.

"Our statewide nitrate load has increased over the last 20 years or so, and part of that is due to an increase in the number of livestock animals that we have, especially hogs," Jones said.

He was part of the team that released a study last year that showed nitrogen pollution flowing from Iowa to the Gulf of Mexico had grown by close to 50% over nearly two decades.

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The state has spent millions of dollars trying to reduce the level of nitrates and phosphorus entering Iowa's waterways and eventually contributing to the Gulf of Mexico dead zone each summer.

"We have the equivalent of 168 million people here ... the scale of that's so enormous, we have no margin for error when it comes to water quality," Jones said.

Even with the large amount of livestock manure being generated in Iowa, it still provides only about one-third of "the state’s needs for nitrogen and phosphorus," said Daniel Andersen, an Iowa State University associate professor of manure management and water quality.

Iowa, the nation's largest corn grower, is expected to plant 13.6 million acres to the crop this year.

The rest of farmers' fertilizer needs are met through synthetic or commercial fertilizers, Andersen said. "There is sufficient cropland to utilize all our manure as a fertilizer."

Jones acknowledges that livestock production helps rural economies, and manure is a good fertilizer that promotes healthy soils.

But manure can be more difficult to manage, he said, especially with extreme weather. For example, full confinement pits can mean farmers are applying manure to snow-covered fields, a time when fertilizer is more likely to wash into nearby streams.

"Managing the waste from these animals is possibly our state’s most challenging environmental problem," Jones wrote in his first blog calculating Iowa's fecal equivalent population.

Donnelle Eller covers agriculture, the environment and energy for the Register. She can be reached by email at deller@registermedia.com or by phone at 515-284-8457.