Sept. 9, 2009 -- It's the ultimate in recycling. Take some wood ashes from the fireplace, add a little of your own urine and spread it around your tomato plants. You may get a blockbuster crop.

Scientists in Finland have found that wood ash and human urine perform just as well as more expensive mineral fertilizers, at least for some crops, while doing less damage to the environment. The combination is rich in nutrients, nitrogen, phosphorus, potassium, calcium and magnesium. The researchers raised a healthy crop of tomatoes in a carefully controlled series of laboratory experiments.

Other research has shown that human urine is an effective substitute for synthetic fertilizers, at least for cucumbers, corn, cabbage, wheat and tomatoes. Ash has also been shown to be useful in agriculture.

But the Fins say they are the first ones to combine urine with wood ash, and plants treated with that substitute performed four times as well as unfertilized plants and left the soil less acidic. The scientists insist it's safe and doesn't pose "any microbial or chemical risks."

Finding Could Be Boon to Developing Countries

But what do tomatoes raised on human urine taste like? Just like ordinary tomatoes, according to a panel of 20 daring folks who concluded they couldn't tell any difference.

The finding could be a boon to third world countries by drastically reducing the cost of fertilizer, and the lead scientist reported via e-mail that people in poor countries may be more likely to build toilets now because they could reuse their urine.

"Our study demonstrated that the construction of a toilet is not an expenditure, but it is an investment to get fertilizer," Surendra Prahan of the University of Kuopio in Finland said. The study was published in the current issue of the American Chemical Society's Journal of Agricultural and Food Chemistry.

But why human urine? Well, because there is so much of it, and it's easy to collect.

"It is available or formed in every household, even in houses with poor people," Prahan said. A similar result could result from using cattle urine, but that's a lot more difficult to collect. And, of course, chicken urine is out of the question.

Don't Try This at Home

Apparently, human urine really packs a punch.

"Urine from a single human individual could fertilize some 6,300 tomato plants, which could produce 2.41 tons of tomato fruits" in just one season, the study notes.

One reason people may not want to try this at home is human urine can carry pathogens if the donor is severely infected.

"But most pathogens can be inhibited or killed if the urine is stored for one to two months," Prahan said. Urine contains urea, which turns into ammonia in a few hours or days, which kills pathogens, Prahan added.

Tomatoes were chosen for the experiments "because it has a worldwide distribution, it is commonly cultivated in home gardens, and it is a common ingredient in many recipes," the researchers said.

The plants were grown in four different ways in a greenhouse on the Kuopio campus. Some received no fertilizer, some received commercial fertilizer, some received just urine, and others received human urine and birch ash collected from the furnace in the home of one of the participants.

No Harmful Substances Found

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.

All Tomatoes Rated "Equally Good"

"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.