How Waste Could Replace Synthetic Fertilizers in U.S. Agriculture

For many decades, modern agriculture has depended on synthetic fertilizers to maintain high crop yields. These products are now so fundamental that one simple fact is often overlooked.

Farms are already part of a natural nutrient cycle, but people have largely failed to make use of it.

New research from Cornell University puts that cycle back in the spotlight. It finds that nutrients currently flushed away or thrown out could make a significant contribution to feeding crops throughout the United States.

Waste can replace fertilizers

Waste is generally viewed as a disposal issue rather than a resource to be reused. Yet, on closer examination, researchers identified a vast pool of recoverable nutrients in animal manure and human waste.

If they were recovered in full, these materials could provide every bit of nitrogen required by U.S. agriculture and roughly half of its phosphorus needs. Financially, that would amount to fertilizer worth billions of dollars each year.

The result calls a longstanding belief into question. Nutrients are not in short supply; the problem lies in how they are managed and moved.

Nutrients unevenly spread

The difficulty is obvious on a map. Nutrients commonly accumulate in areas with high population density or major livestock businesses.

By contrast, key agricultural areas are frequently located a long way from those sources. The Midwest and sections of the Great Plains, for instance, continue to depend strongly on synthetic inputs because there is little nutrient supply nearby.

“This is a coordination problem, not a resource problem,” said study co-author Professor 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.”

Put simply, the nation already possesses the required resources, but it is not transporting them effectively.

Waste as a local fertilizer

Although the national view reveals an imbalance, the local situation is more encouraging.

A considerable proportion of nutrients could be reused near the places where they originate. In many instances, farms in the surrounding area could take up this supply without lengthy transport journeys or major expense.

Transporting nutrients into neighbouring regions is also feasible when local use alone is not enough.

To investigate this in greater detail, the research team produced detailed maps. They mapped waste production alongside crop requirements across numerous regions and crop types.

Their method showed that many reuse opportunities are available over comparatively short distances.

The principle is straightforward: rather than moving synthetic fertilizers through extended supply chains, make use of resources already available locally.

Pollution links to inequality

The research further highlights a relationship between nutrient distribution and social circumstances. Places with surplus waste often experience greater pollution when nutrients seep into lakes and rivers.

Conversely, areas without a natural nutrient supply rely more heavily on chemical fertilizers, which may damage soil and water over time. These trends frequently coincide with less affluent communities.

“The nutrient inequality seems to mirror social inequality in a large sense,” Liao said. “So potentially fixing the nutrient flow can promote environmental justice.”

Making nutrient movement through the system more effective could therefore do more than improve agricultural efficiency. It could limit environmental damage while helping vulnerable communities.

Local waste fertilizer systems

What might an improved system involve? The researchers recommend smaller, localised arrangements instead of a single nationwide network.

Treating waste close to where it is generated and applying it to nearby farmland could keep the approach both practical and efficient.

A basic example demonstrates the idea. A livestock farm encircled by arable fields already contains all the elements needed for a closed-loop system.

With an appropriate system in place, animal waste could provide nutrients directly for the crops.

Waste systems need coordination

“We’re advocating for a decentralized system, so that waste can be processed locally,” Liao said.

“But in order to do this, we need to coordinate across different sectors such as agriculture, waste and energy. The technology is there, but we need governance and infrastructure to scale up to the entire U.S.”

This model would lessen dependence on long supply chains and allow nutrients to keep circulating within a region.

Waste can reduce chemical fertilizer use

The study comes at a point when the global fertilizer supply is still costly and uncertain. Manufacturing synthetic fertilizers also has environmental impacts, including substantial energy consumption and pollution.

“Excessive use of synthetic fertilizers leads to water pollution, and the production itself generates more emissions – it’s a very intensive process,” Liao said.

“And you can see with the Iran War, there are supply-chain issues that can lead to great food insecurity as well.” Reusing nutrients that already exist, by comparison, could offer a cleaner and more reliable option.

This transition will not occur immediately. It needs planning, infrastructure and collaboration between sectors. However, the underlying concept is clear.

The nutrients already exist. The task is to learn to use them more effectively.