A new study from Cornell University reveals that human and animal waste could theoretically replace a massive portion of synthetic fertilizer in the US.
Researchers found that human and animal waste could provide 102% of the nitrogen and 50% of the phosphorus needed to fuel the nation’s entire agricultural industry.
At today’s prices, the study says that this untapped waste represents a $5.7 billion economic boon waiting to be reclaimed.
Shifting away from synthetic fertilizers reduces energy-intensive production, lowers greenhouse gas emissions, and stabilizes supply chains impacted by international conflicts.
“Excessive use of synthetic fertilizers leads to water pollution, and the production itself generates more emissions – it’s a very intensive process,” said Chuan Liao, corresponding author and assistant professor.
“And you can see with the Iran War, there are supply-chain issues that can lead to great food insecurity as well,” the author added.
Geography of waste
Human and animal waste are rich in the three primary nutrients plants need to grow: Nitrogen (N), Phosphorus (P), and Potassium (K).
While the resource is abundant, the primary challenge is coordination across geographies.
There is a spatial mismatch between where waste is produced (densely populated cities and livestock hubs) and where it is needed (agricultural regions like the Midwest and Great Plains).
“This is a coordination problem, not a resource problem. Even considering the real-world constraints, there’s still a substantial amount of nutrients that can be economically redistributed to meet crop needs,” explained Liao.
Huge surpluses of nutrients congregate in the dense urban corridors of the Northeast and the massive livestock hubs of the West.
Meanwhile, the “Breadbasket” of the Midwest remains in a deep nutrient deficit, forced to rely on expensive, energy-intensive synthetic fertilizers imported from overseas.
The study used high-resolution mapping — focusing on 10-kilometer blocks — to identify these nutrient inequalities.
Interestingly, these maps mirrored social ones. This nutrient inequality frequently overlaps with socioeconomically disadvantaged counties, creating a double-edged environmental burden.
Surplus regions often see waste leak into local waterways, causing toxic blooms. Deficient regions rely on synthetic chemicals that can strip soil health over time.
“The nutrient inequality seems to mirror social inequality in a large sense,” Liao said. “So, potentially fixing the nutrient flow can promote environmental justice.”
Decentralized solution
Raw waste cannot simply be dumped on fields due to the presence of pathogens and its high water content.
Experts advocate for a decentralized system. Instead of shipping heavy liquid waste across the country, local hubs process the waste into concentrated, dry pellets or liquids that are easier and cheaper to transport to nearby farms.
The research demonstrates that a localized approach is surprisingly efficient: nearly 37% of nitrogen and 46% of phosphorus can be recovered and utilized almost exactly where they are generated.
For the remaining surplus, the team found that more than half can be redistributed to neighboring regions with minimal economic or environmental impact.
This confirms that the majority of these waste nutrients can be returned to the soil without the need for massive, long-distance transport.
The study offers a strategic blueprint to reclaim the untapped value of human and animal waste, providing a sustainable alternative to synthetic fertilizers.
It would not only help national food security but also curb the environmental damage caused by conventional fertilizer manufacturing.
While the necessary technology already exists, the study highlights that success hinges on new governance and infrastructure to coordinate the agriculture, waste, and energy sectors.
The findings were published in the journal Nature Sustainability on April 15.