Sep 25, 2024

Study: Human urine could be used as fertilizer

Bacterial communities in soil are as resilient to human urine as synthetic fertilizers – making recycling the bodily fluid as a fertilizer for agricultural crops a viable proposition, according to a new study.

Scientists discovered that, even when applied in high doses, one-year stored urine had little impact on soil bacterial communities and produced minimal change in soil pH and salinity, according to the study.

However, the researchers did discover that urine fertilization increased the relative amounts of nitrifying and denitrifying groups compared to synthetic fertilizer — implying that more nitrogen oxides could be emitted when fertilizing with urine, according to a news release.

Publishing their findings in Applied Soil Ecology, the team of researchers from University of Birmingham and L’Institut Agro Montpellier, France, call for further studies on the long-term effects of urine fertilization — particularly regarding nitrogen oxide production and soil salinity.

“Our research highlights the potential of recycling human urine to enhance agricultural sustainability, reduce wastewater pollution, and decrease reliance on synthetic fertilizers. Stored urine can be safely applied to a plant-soil system without negatively impacting the soil microbiome,” University of Birmingham’s Manon Rumeau said in the release.

Fresh urine is composed of 95 % water with the remaining 5% made up of amino compounds, such as urea or creatinine, organic anions and inorganic salts making it a source of bioavailable nutrients and micronutrients for plant growth, according to the release.

There has been great interest in re-using human urine as a crop fertilizer. However, until the publication of the study, more understanding was required on how urine can affect soil functions and microbial communities.

Scientists fertilized a spinach crop with two different doses of a source-separated and stored human urine, comparing these with a synthetic fertilizer treatment and a water treatment without fertilization, conducted across four soil tanks in greenhouse conditions, according to the release.

After 12 months of storage, urine had a depleted microbiome but contained few common strains of urine. Thud storing urine for several months, with the resulting increase in its pH value (about 9 rather than 6.5 for fresh urine) and its free ammonia concentration, is considered sufficient to inactivate most human pathogenic bacteria and break down extracellular DNA, according to the release.

Soil bacterial communities were resistant to urine fertilization with only 3% of groups of organisms impacted. The urine’s high salt concentration had little discernible effect on the bacterial community, according to the release.

“Unveiling the impact of human urine fertilization on soil bacterial communities: A path toward sustainable fertilization” is published by Manon Rumeau, Chiara Pistocchi, Nassim Ait-Mouheb, Claire Marsden and Brigitte Brunel.

Rumeau is a Ph.D candidate in physical geography working on a project examining biological nitrogen fixation in forest soils under elevated CO2: response of a key soil nutrient to global change.