Urine was collected from several "eco-toilets in private homes," the study says, and stored for about six months while the researchers analyzed its "microbiological properties." No harmful substances were found.
During the growing period the plants that received commercial fertilizer and those that got the urine and ash performed about the same, substantially higher than the ones that got only urine, and four times greater than the unfertilized plants.
But the plants that got only urine had a "significantly higher" protein content, leading the researchers to conclude that either urine with ash, or plain urine, would work much better than no fertilizer at all. And it's cheap.
All the plants were irrigated every day with lake water and their flowers were hand pollinated every morning "with the help of a soft brush." Harvesting began on the 62nd day and ended on the 88th day.
Twenty individuals were recruited to test the taste after they had demonstrated that they could recognize basic tastes of sweet, sour, salty and bitter.
"The panelists did not prefer any particular samples, and all tomato samples were evaluated as being equally good by the tasters," the researchers said.
The scientists did not provide a recipe for their favorite fertilizer, but they did suggest a few precautions.
It's probably not a good idea to dash out to the greenhouse after too much coffee and administer the treatment directly. Urine needs time to naturally immobilize any pathogens, so store it in a jar or suitable container for at least a couple of months.
And don't spray it directly on the plants because it could burn them. Instead, rake it into the soil. Then, one of these days, bite into a plump tomato and it will all come back to you. Now that's recycling.