Human Pee Makes Surprisingly Good Fertilizer


The world is in shortage of fertilizers. The dilemma is linked to the war in Ukraine, which affects the export of ingredients like potash and phosphate. The price of fertilizers has risen by about 30% since the beginning of the year, which has increased the cost of foodstuffs. Rising fertilizer prices also threaten to cause food shortages in developing countries.

Farmers must fertilize crops to maintain food supplies at adequate levels. New research shows that our own waste could be an effective tool for doing this, especially human urine.

Researchers from Niger’s National Agricultural Research Institute recently published research on the use of urine as fertilizer for crops of pearl millet, a cereal commonly grown in the region. Urine contains phosphorus, potassium and nitrogen, which are widely used for crop growth. Scientists processed the urine and tried using it as a fertilizer for three years and found that it increased yields by around 30%.

Scientists treated urine by simply storing it at just over 70 degrees Fahrenheit for two to three months. The pH of urine increases over time as urea, a nitrogenous compound, hydrolyses to ammonia, which sanitizes the urine. It can then be used as fertilizer.

The thought of peeing on plants may conjure up images of dead grass where dogs have relieved themselves, but that’s because of the salt content of urine hitting the living parts of a plant. Treavor Boyer, an associate professor of sustainable engineering at Arizona State University who was not involved in the previously mentioned study, told Popular Science. It’s about how you use urine.

“The salt on the leaves and stems burns the plant. This is the biggest challenge. Urine contains salts,” Boyer says. “If you apply liquid urine with salts in it, you don’t necessarily want to spray it on the plants, but apply it to the soil so that it gets to the roots. If there is enough irrigation in place, it will flush out the salts as they are quite mobile in the soil. They don’t stay. And then the nutrients stay in the soil.

[Related: Diverse microbes are key to healthy soil. Climate change is threatening that.]

Nancy Love, a professor of civil and environmental engineering at the University of Michigan who also wasn’t involved in the study, told Popular Science that using urine as a fertilizer appears to be relatively safe when used. is handled appropriately. She says any viruses and bacteria in the urine, such as E. coli, that might be of concern are not a problem for humans after the treatment process. In his lab, they pasteurize urine by using heat to process the urine instead of just storing it.

One problem, Love says, is the “ick factor.” People don’t like the idea of ​​eating food grown with urine-based fertilizer. People may not understand that it is being treated and that it is not going to make them sick. Love says it’s just a messaging problem, but the urine can also be used to fertilize crops that won’t become food for humans either.

“It could be used to fertilize food for animals that then become food or in other places where you fertilize non-food crops,” Love explains.

Historically, urine has been used as a fertilizer for thousands of years in parts of Africa and Asia. Today, urine as fertilizer is experiencing a bit of a resurgence. Pilot projects are emerging in the United States, Europe and Africa. Many are interested in replacing chemical fertilizers because the production of synthetic nitrogen present in these fertilizers contributes to greenhouse gas emissions, which is not a problem with urine.

These projects are small, but Boyer says we could scale up if we had more waterless urinals that can capture and divert urine without dilution.

“In the United States, we have waterless urinals, but they’re really only used for water conservation. They’re not really used as part of a urine collection system,” says Boyer. “We need to have plumbing fixtures that allow us to collect urine separately from the rest of the wastewater. That urine would need to be stored in a building, probably, and then used onsite in a reduced fashion or there needs to be a logistics system in place to collect that urine and use it in a beneficial way that starts to become economical.

Love says it’s unlikely that urine-based fertilizers will take the world by storm anytime soon, and it’s also unlikely that we’ll start replacing every urinal with one that could help achieve those goals. Still, pee-collecting urinals could become more common in new and remodeled buildings.

“What we don’t want to do is rebuild our infrastructure with 50s, 60s, or 70s technological thinking about water systems,” Love says. “What we want to do is advance technology and advance government policy.”

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