DES MOINES, Iowa (AP) — Iowa leads the nation in the amount of human and animal waste it produces, and the management of animal manure continues to be a pressing environmental concern, according to a University of Iowa research engineer.

Chris Jones' study found that the state — with 3.2 million people and a total livestock population of 110 million — produces as much manure as a human population of 168 million, the Des Moines Register reported.

"Just to ensure clarity, in Iowa, we are generating as much fecal waste in every square mile as 2,979 people," Jones wrote in a blog on the university...