Human urine mixed with wood ash makes a potent, inexpensive fertilizer without risk of disease, scientists in Finland have learned. The mix can be safely substituted for expensive synthetic fertilizers to produce abundant crops, researchers at the University of Kuopio said. During the winter of 2007-08, researchers Surendra Pradhan and Helvi Heinonen-Tanski collected human urine from several eco-toilets in private homes, storing the urine for six months at 45 degrees Fahrenheit.

Results of the first study evaluating the use of human urine mixed with wood ash as a fertilizer for food crops has found that the combination can be substituted for costly synthetic fertilizers to produce bumper crops of tomatoes without introducing any risk of disease for consumers.