Human urine could grow green beans on Mars

Mineral struvite in urine is an excellent fertiliser for green beans. Image: Bob Bowie / Unsplash.

Astronauts may dream of living and working on the Moon or planet Mars, but what are they going to eat out there, and how are they going to grow their food?

A circular agricultural ecosystem for food production will be essential, and a research team in the Netherlands is investigating how to grow crops in a sustainable way, using local resources. Their latest study shows that applying human urine in the form of the mineral struvite could boost the growth of green beans on Mars and the Moon.

"The human urine we used in the study was collected from portable toilets at festivals in Amsterdam."

Wieger Wamelink, Wageningen University

The research team at Wageningen University & Research used simulant regoliths - the biologically active upper layer of soil - instead of real Mars and moon regoliths for their experiments. Mars regolith is not available on Earth, and although there is some Moon regolith on earth, it is not present in the quantities needed for a crop growth experiment.

Wieger Wamelink, principal investigator of the study, said, "The human urine we used in the study was collected from portable toilets at festivals in Amsterdam.

View of the experimental set-up, including an automatic watering system. Image: Wieger Wamelink

"You can imagine that there all kinds of substances in urine that we would not like to use in crop fertiliser, so we used struvite instead - a mineral that is extracted from human urine and consists of magnesium ammonium and phosphate and that is almost 100% pure, so it doesn’t bring along any contaminations, like medicine remains or drugs. It releases the nutrients slowly during the whole growth period."

However, both real regoliths and their simulants lack significant quantities of ammonium, nitrate and phosphate, which are essential for a proper plant growth.

"We have proven that struvite can be an excellent manure. In this way, we can easily process and apply human urine as fertiliser in the regoliths," said Wamelink." It boosts plant growth and can increase bean harvest with several factors on the regolith simulants."

The researchers said that they did not taste-test the green beans, firstly because at the point of harvest, struvite was not officially allowed to be used as a manure for crops. Secondly, regoliths and their simulants contain quantities of poisonous metals which could end up in the beans.

Sample of struvite. Image: Wieger Wamelink

More research on the contamination of the crops with heavy metals from the regolith is needed.

Because there are only ice and regolith, with no organic matter available on Mars and the Moon, the soils have to be amended and improved to make crop growth possible. What is needed is a closed sustainable agricultural ecosystem.

One of the key factors in this system will be the recycling of human waste.

"By applying struvite extracted from human urine, we can fill in one of the steps in the golden circle of crop growth on Mars and the Moon, but also here on Earth," said Wamelink, adding that human urine could be applied as fertiliser instead of being wasted.

Research dome

As a next step, the recently started BASE project aims to set up a Moon-Mars dome containing all necessities to grow crops at Mars or the Moon, indoors.

This dome is a research facility to test innovations and make them work together as a circular system. Its blueprint could be applied on Mars or on the Moon, but also on planet Earth, for example, in deserts or at the South Pole.

The Food For Mars and Moon project investigates how to grow crops on both celestial bodies, applying the resources available at hand - regolith and ice. The research team has already grown a whole series of crops on simulant regoliths, including potatoes, carrots, peas, tomatoes, garden cress and radish.

The project is now in the phase of making crop production fully circular, which includes the application of pollinators, bacteria, fungi and earthworms.

The study was published in Open Agriculture journal.