In a greenhouse in Grossbeeren, Germany, scientists have shown that vegetables can grow just as well using fertilizer made from human urine and poop as they do with synthetic chemicals — and sometimes even better.

Caroline Ganglo and Stefan Karlowsky from the Leibniz Institute for Horticultural Sciences (IGZ) grew kohlrabi, a leafy vegetable related to cabbage and broccoli, using a combination of treated human urine and compost made from fecal matter. Their study, published in Frontiers in Environmental Science, found that the plants grew just as big and produced the same harvest as those grown with conventional mineral fertilizer.

But that's not all. The plants also absorbed 13% more nitrogen — a key nutrient for plant growth — compared to the conventionally fertilized group. Meanwhile, the soil retained more organic nitrogen (25% higher at harvest) while having five times less mineral nitrogen that could wash away and pollute waterways.

The researchers say this matters because many European countries currently rely on mineral fertilizers imported from far away. These fertilizers are often made from fossil fuels, come with volatile price swings tied to geopolitical conflicts, and have to travel long distances to reach farms. Using human waste as fertilizer could change that.

"Instead of treating urine and fecal matter solely as waste streams, they can become sources of nitrogen and phosphorus for agriculture," the study notes.

Some people worry about safety — could medicine residue or other contaminants end up in food? The team checked this carefully. They tested for doxycycline, an antibiotic that can survive in fecal matter, and found it did not transfer to the edible parts of the kohlrabi in detectable amounts.

The study was part of a larger European project called P2GreeN, which explores ways to close the loop between sanitation and food production. Dr. Stefan Karlowsky, who co-coordinated the project at IGZ, said the findings add to growing evidence that recycled fertilizers from human excreta can work for growing crops without sacrificing yields.

Still, the scientists say more research is needed. Long-term studies will help answer questions about how repeated use affects soil salt levels, soil carbon, nitrate leaching, and the behavior of other trace substances over time. The results could eventually inform new regulations that make it easier for farms to use recycled fertilizers — a step toward a more circular food system where waste becomes resources again.