BIRMINGHAM, United Kingdom – Human urine has the potential to be an eco-friendly crop fertilizer, according to recently published research from the University of Birmingham in the United Kingdom.

“Our research highlights the potential of recycling human urine to enhance agricultural sustainability, reduce wastewater pollution, and decrease reliance on synthetic fertilizers,” said Manon Rumeau, doctoral student in soil biogeochemistry at the University of Birmingham.

Using human urine as fertilizer has been researched globally, with some groups claiming that it’s a practice tracing back to ancient times. Although urine is 95 percent water, it also contains compounds that make it a good source of nutrients for plants. For example, urine contains urea, a compound with high nitrogen content already widely used in the agricultural industry. Other nutrients present include phosphorous and potassium.

The first scientific experiment using human urine as a fertilizer was published in 1994, detailing the chemical composition of urine and its efficiency as fertilizer. The researchers noted that nitrogen from urine was absorbed less in barley plants than nitrogen from ammonium nitrate. However, phosphorus from urine was absorbed by plants better than phosphorus from regular fertilizers. Since this initial study, the value of urine as fertilizer has dramatically expanded, with numerous studies reporting increased crop gains, plants that grow faster, and greater yields.

Still, much remains to be discovered before widespread implementation and recommendation of urine fertilization. Rumeau and her team focused on understanding whether human urine impacts soil functions and important microbial communities present in the soil. Rumeau said the project was motivated by finding an easy way to use urine without adulterating it. The urine was sourced from a startup called Ecosec, which manufactures and sells dry toilets that allow for the easy separation of waste products for collection.

“(Collecting urine) from source-separating toilets or urinals is imperative to prevent contamination with feces that contains much more pathogens than urine,” Rumeau said. “Then the storage (of the urine) needs to be done in an air-tight container to prevent the volatilization of nitrogen and the smell as well.”

To study how untreated urine impacted soil, a spinach crop was fertilized with two different doses of source-separated and stored human urine and compared with a synthetic fertilizer and a water treatment without fertilization. Urine and soil bacterial compositions were assessed at the beginning and end of the study period.

“We found that soil microbial diversity was not affected by urine fertilization despite the high salinity in urine, notably,” Rumeau said. “Even though this will need to be confirmed by long-term experiments, this finding is very encouraging for the re-use of urine as a fertilizer.”

The researchers also report that after 12 months of storage, the urine had a depleted microbiome. Over time, the urine’s pH value is increased, and the free ammonia concentration of the urine is considered sufficient to inactivate most human pathogenic bacteria. Currently, the World Health Organization recommends sanitation of urine before being used to fertilize produce for public consumption, either through storage at 68°F for six months or pasteurization.

Americans are estimated to produce 90 million gallons of urine daily, making it a readily accessible and cheap fertilizer option. Some researchers have estimated that 330 tons of nitrogen and 20 tons of phosphorus a day could be retrieved if 10 percent of the U.S. population collected their urine. However, Rumeau notes that one potential issue is the transportation of urine. Given that it is 95 percent water, urine would be bulky and costly to transport. A practical solution for smaller farms would be establishing their own urine collection systems on-site.

In the U.S., the Rich Earth Institute based in Vermont collects about 12,000 gallons of urine annually from donors, implementing the first community-scale urine recycling project. Since 2012, the institute has been applying sanitized urine to hay fields in the Brattleboro area, according to the group’s website. Additionally, with funding from the USDA, the group has quantified the effects of pure and diluted urine on crop yield. The group also offers webinars to provide information on how to fertilize gardens with urine and offers urine collection kits. Still, it’s likely to be some time before human urine fertilization becomes a common and recommended practice, and more research is required before widescale implementation.