Cyanobacteria-based fertilizer yields 27 times its weight in duckweed

One gram of cyanobacteria. Twenty-seven grams of duckweed. That is the number the ZARM team published in the Chemical Engineering Journal this month, and it is the one you will see quoted in every article about this study. It is also, honest assessment requires saying so, a lab result under controlled Earth conditions for a plant that grows fast by definition. On Mars, none of those conditions apply.

The research — led by Tiago P. Ramalho, a PhD student in the Department of Environmental Process Engineering at the University of Bremen, and Prof. Cyprien Verseux at the Laboratory of Applied Space Microbiology at ZARM — addresses one of the genuinely hard problems in Mars colonization: the nitrogen cycle. Martian regolith simulant, known as MGS-1, contains no bioavailable nitrogen. Martian atmosphere is mostly carbon dioxide. Without fixed nitrogen, nothing grows. You cannot truck fertilizer to Mars in useful quantities. You have to build the cycle from local resources, which is what this team attempted to do.

The approach, published as "Sustainable Mars agriculture: Fertilizer production from cyanobacterial biomass via anaerobic digestion" (Chemical Engineering Journal, DOI: 10.1016/j.cej.2026.174922), works like this: cultivate cyanobacteria using atmospheric inputs available on Mars — CO2, water ice, trace nitrogen from the regolith itself — then ferment that biomass through anaerobic digestion. The digestion releases ammonium. The ammonium is applied as fertilizer to duckweed (Lemna sp.) growing in MGS-1 simulant. The byproduct of digestion is methane, which the researchers note could be captured as an energy source for subsequent cycles.

Optimal fermentation conditions, as the paper reports, were 35 degrees Celsius and a 5 millimolar ammonium concentration — parameters the team arrived at after systematic testing. Pre-heating the cyanobacteria biomass before fermentation accelerated decomposition. These are real engineering parameters with real energy implications, and they are worth stating plainly: 35 degrees Celsius is substantially warmer than average Martian surface temperature, which at the equator ranges from roughly 20 to minus 153 Celsius depending on season and time of day. Maintaining that temperature on Mars requires continuous heating energy. That cost is not accounted for in this paper. Neither is the energy required to provide sufficient light for photosynthesis.

Duckweed is a defensible choice as a test crop. It grows quickly, reproduces asexually, and produces protein-rich biomass — it has been consumed as food in parts of Southeast Asia for centuries. Its low, flat growth habit minimizes structural requirements. None of this makes it a practical primary food source for a Mars mission. It is a proof-of-concept organism for a closed-loop nitrogen cycle, nothing more.

What Ramalho and Verseux have demonstrated is that the cycle can be made to work at small scale in a lab. The conversion ratio of 27:1 is real. The methane byproduct is real. The fact that they used no Earth-sourced fertilizer is real. What remains unaddressed at this stage is the energy accounting: how many kilowatt-hours does it take to grow, harvest, ferment, and re-inoculate per gram of edible protein produced? That number will determine whether this architecture is viable on Mars or interesting in a journal.

"You can imagine a vegetable garden on Mars that is run entirely from local resources — without bringing soil, fertilizer, or water," Ramalho told Universe Today. The framing is accurate as far as it goes. What it elides is the energy infrastructure required to run that garden, the radiation shielding for the biological components, and the contamination control protocols needed to prevent Earth microbes from outcompeting the cultivated system. These are not minor footnotes. They are the next research gate.

The study is a solid piece of engineering groundwork. The nitrogen cycle problem for Mars agriculture is real and understudied, and solving it in stages — first proving the chemistry works, then optimizing energy balance, then addressing the radiation and thermal environments — is the correct sequence. What the paper is not is a demonstration that sustainable food production on Mars is solved. The 27:1 mass conversion is the easy part. The hard part is still ahead.