Cornell Study Finds That Human and Animal Wastes Could Replace Nitrogen Fertilizer
For years, the chemical fertilizer industry has claimed that organic farming can’t feed the world. Why not? Because, they always said, there weren’t enough organic wastes to supply enough fertility—especially nitrogen—to crop fields.
A new study by a group of Cornell University researchers challenges that long-held assumption. In their paper, “Realizing an Equitable Circular Bionutrient Economy in the United States,” the researchers estimated the amount of nitrogen and phosphorus contained in human and animal wastes in the United States, then compared those numbers to typical fertilizer recommendations for fifteen major crops.
The results? Those wastes contain enough nitrogen to meet 102 percent of fertilizer recommendations and 50 percent of the recommended phosphorus. Those numbers are, of course, theoretical; actually getting the wastes to cropland can create some logistical challenges. But they estimate that “more than half of the surplus nutrients can be redistributed to nearby regions with low economic and environmental costs.”
“This is a coordination problem, not a resource problem,” said corresponding author Chuan Liao. “Even considering the real-world constraints, there’s still a substantial amount of nutrients that can be economically redistributed to meet crop needs.”
And that’s just human and animal waste—aka biosolids (sewage sludge) and manure. The study didn’t even look at food waste, organic industrial wastes like slaughterhouse byproducts, crop residues, or green manure—all of which are also important fertilizers that are high in plant nutrients.
As prices for nitrogen fertilizer continue to climb far above the five-year average because of supply shortages caused by the war in Iran, the American Farm Bureau Federation reports that 70 percent of farmers can’t afford to buy as much nitrogen fertilizer as their current cropping systems demand. The National Corn Growers Association found that farmers are already worrying that they won’t be able to purchase enough nitrogen for the 2027 season, either.
As Liao points out, more than half of American farmers might be able to meet their nitrogen fertilizer needs without buying any synthetic nitrogen. “With the right infrastructure and incentives, waste from the pig farm could be used to satisfy the nutrient-hungry corn fields right next door.”
For eco-farmers, that’s old news. Organic farmers have demonstrated for years that it’s totally possible to raise healthy, high-yielding crops with organic fertilizers. Even the most anti-organic scientists always admitted that manure was a good fertilizer; they just claimed that there wasn’t enough. But as this new study shows, that claim was never based on actual data.
If the price of synthetic nitrogen continues to rise, farmers might have to ditch the anhydrous ammonia tank for the manure spreader. And when they do, they’ll be one step closer to transitioning to organic.
