Once seen as taboo, human urine is quietly making a comeback in agriculture. Scientists and sustainability advocates say this overlooked resource could help close a vital nutrient loop, ease dependence on synthetic fertilizers and reduce the environmental costs of modern wastewater treatment.
A Rediscovered Resource
A trio of recent studies bolsters the case for urine reuse.
In a field trial published in the Journal of Agricultural and Food Chemistry, researchers compared synthetic fertilizer and urine-only and urine-supplemented fertilizers on snap beans and turnips in Florida. The results were clear: Urine-only plots outperformed the no-fertilizer control, and urine-supplemented treatments matched synthetic fertilizer yields.
Meanwhile, researchers in a 2023 study created a liquid fertilizer from nitrified urine and graywater and used it to grow hydroponic lettuce. When key nutrients like phosphorus and potassium were added to the mixture, lettuce yields reached 103% of the control grown with commercial fertilizer. Importantly, the surfactants present in the graywater posed no toxicity risk after biological treatment.
These findings echo the projections made in the report, “Willingness among food consumers to recycle human urine as crop fertiliser: Evidence from a multinational survey,” which emphasized not only technical viability but also public acceptance. In a global survey, 68% of respondents supported recycling urine, and 59% were willing to eat crops fertilized with it.
“Urine is this relatively easy way of capturing a nutrient from human excreta for use,” says Carol Steinfeld, author of “Liquid Gold: The Lore and Logic of Using Urine to Grow Plants.”
“Often it has more nitrogen in it than feces. Feces are more about carbon and maybe phosphorus,” she says.
Steinfeld says her book was inspired by pioneering Swedish studies on the safe and effective use of urine as fertilizer. Those studies helped establish holding times and sanitization protocols that make urine use safe in agriculture. For example, urine stored for one to six months naturally sanitizes itself by killing off most pathogens, especially when stored at ambient temperatures, Steinfeld says.
“Swedish sanitary researcher Jan Olof Drangert found that in Western cultures, children today do not have an innate aversion to urine,” Steinfeld says. “It’s a learned behavior — one we developed for good reasons, like pathogen avoidance. But urine carries very few pathogens compared to feces. The risk is much lower.”
In urban settings, where soil fertility and water access can be limited, urine has gained quiet traction among permaculturists and eco-conscious gardeners.
“I meet people who have adopted the term ‘liquid gold’ for their home practices,” Steinfeld says. “They’re collecting their own urine, mixing it with graywater and applying it to mulch or gardens. It’s informal, but it’s happening across the country.”
According to the Rich Earth Institute, which operates out of Vermont, human urine has been successfully applied to hayfields without causing nitrogen leaching into groundwater. The report, “Reclaiming the Value of Urine for Agriculture,” showed that, “Rich Earth’s field tests on hay over several years have shown equivalent yields between urine-fertilized and chemically-fertilized test plots, both significantly higher than unfertilized plots.”
The Wastewater Problem (and Farming Solution)
Steinfeld argues that agriculture — particularly rural or peri-urban farms — is key to mainstreaming urine reuse.
“Right now, wastewater treatment plants spend enormous amounts of energy just to remove nitrogen from urine,” she says. “In places like Palo Alto, Calif., the city’s largest power bill is from its wastewater plant trying to denitrify its effluent. If residents used urine-diverting toilets, the city could cut its energy costs dramatically.”
These specialized toilets, common in Sweden and now available in the U.S., separate urine at the source. From there, it can be transported to farms as a high-nitrogen fertilizer, reducing the need for synthetic products like urea, which require fossil fuel-intensive processes to manufacture.
“Why not take that municipal challenge and bring it to a farm growing corn or hay?” Steinfeld says. “The farmer wins. The city wins. We close the nutrient loop.”
Scaling Up: From Cornfields to Cover Crops
Though most current use is limited to gardens and research plots, the potential for broad-acre application is growing. Trials at the University of New Hampshire, Cornell University and the Rich Earth Institute have shown promising results in applying human urine to pasture, cover crops and even corn.
“Researchers in Sweden demonstrated that urine can be injected into the soil and displace commercial fertilizer,” Steinfeld says. American studies have confirmed that practice can be safe and effective, so long as application rates are managed to prevent runoff.
Phosphorus, another vital nutrient typically found in feces, can also be recovered from human waste streams, but Steinfeld emphasized that urine’s nitrogen content makes it especially valuable.
“We’re literally throwing away a nutrient that’s costing us energy on both ends — removing it from waste and making it synthetically,” she says. “This is a low-tech fix with high-impact potential.”
The biggest barrier? Perception
Still, despite science and economics aligning, the “ick factor” remains a formidable barrier.
“Even when people agree it’s safe and useful, cultural norms around excreta are strong,” Steinfeld says. “But that can change. In fact, it already is.
“Farmers are well positioned to be the big helpers here,” she adds. “And they should be paid to help. Or someday, they might even pay to get it.”
