In the study in Nature Sustainability, researchers found that animal and human waste in the U.S. could theoretically meet 102% of nitrogen and 50% of phosphorus needs for the nation's agriculture, a value of more than $5.7 billion annually. But they also identified a major hurdle: a frequent mismatch between the location of the waste—often in areas densely populated with people or livestock—and agricultural regions with the highest fertilizer needs.