Your recycled pee may be better for crops than synthetic fertilizer

We know that the agricultural industry has a massive greenhouse gas problem. Now, more research suggests that there is a potentially easy method to cut it down. The promising solution? Simply swap out synthetic fertilizer for fertilizer made using human urine.

Synthetic nitrogen fertilizers are ubiquitous in modern farming due to their affordability and effectiveness, but those conveniences come at a cost. Manufacturing them often generates huge amounts of harmful emissions such as carbon dioxide, methane, and nitrous oxide. Nitrous oxide is particularly problematic, as experts estimate the gas exerts as much as 265-times the effect of CO2 on the environment.

[Related: Wastewater could be the secret to eco-friendly fertilizer.]

In recent years, researchers investigating alternative, eco-friendly fertilizers have started advocating for a natural, if slightly unconventional, replacement: human pee. This is due to urine’s chemical composition, which is roughly 95-percent water and 5-percent amino compounds like urea, creatinine, organic anions, and inorganic salts. In the proper amounts, those compounds can provide plants with valuable micronutrients. Despite knowing this, however, researchers weren’t entirely sure how human pee might affect a soil’s overall functions and microbial communities.

But according to an agricultural study published in the September issue of Applied Soil Ecology, soil microbiome samples not only remain as resilient to urine as they do to synthetic fertilizers, but the bodily waste may even benefit them more.

To test the pee’s efficacy, a team from the UK’s University of Birmingham and France’s L’Institut Agro Montpellier grew four spinach crops over one year—two using different doses of stored human urine, one using synthetic fertilizer, as well as a control that only relied on water treatments without any additives. After 12 months, they then examined the soil health of each sample plot. The team found the urine fertilizers, even in high doses, produced little-to-no adverse effects on the overall microbiome community compared to the other crops, even despite urine’s typically high salt concentration. That said, there were early indications that human pee may generate more nitrous oxides than synthetic fertilizers, although they note that more direct analysis is required to confirm the possibility.

[Related: Pee makes for great fertilizer. But is it safe?]

Despite this, researchers still concluded in their study that urine “can be safely applied to a plant-soil system without negatively impacting the soil microbiome,” and encouraged additional investigations into the long-term effects of urine fertilization. In particular, they hope to learn more about the alternative’s influence on nitrous gas production and salinity accumulation, as well as how those might affect soil microbiomes and plant growth. Meanwhile, recycling urine could even improve larger societal sustainability efforts like water conservation.

“Our research highlights the potential of recycling human urine to enhance agricultural sustainability, reduce wastewater pollution, and decrease reliance on synthetic fertilizers,” study co-author Manon Rumeau, a University of Birmingham PhD candidate in the School of Geography, Earth, and Environmental Sciences, said in a statement on September 23, adding that, “Stored urine can be safely applied to a plant-soil system without negatively impacting the soil microbiome.”