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Using human urine as a fertiliser produces bumper crops of tomatoes that are safe to eat, scientists have found.
Their research was published in the Journal of Agricultural and Food Chemistry last month (August).
Surendra Pradhan, an environmental biology researcher at the University of Kuopio, Finland, and colleagues gave potted tomato plants one of three treatments: mineral fertiliser, urine and wood ash, urine only, and no fertiliser. Urine is rich in nitrogen, phosphorus and potassium.
Yields for plants fertilised with urine quadrupled and matched those of mineral-fertilised plants. The urine-fertilised tomatoes also contained more protein and were safe for human consumption.
"This is a very simple technology. Urine can be collected in a urine-diverting toilet or it can be collected in a separate jerry can [from] an ordinary, pre-existing toilet. If wood ash is available, this can be use as a supplement of phosphorus, potassium and other nutrients," Pradhan told SciDev.Net.
He says that the method is a free alternative to expensive mineral fertiliser, which is also not easily available in remote or hilly areas. Pradhan also believes that the idea could improve sanitation by incentivising toilet-building.
A pilot programme based on the research will be launched in Nepal in November, says Pradhan.
But Håkan Jönsson, eco-agriculture and sanitation system technology expert at the Stockholm Environment Institute in Sweden, told SciDev.Net: "The amount [of urine] that can be collected from a person or a family is fairly small (equivalent to about two bags of fertiliser per year for a west African family).[The technique] is of great value to a subsistence farmer but does not suffice for even a medium-scale cash-crop farm."
He adds that to fertilise larger areas, many urine-diverting toilets would have to be linked up to a good transportation system.
There are also cultural issues. In most cultures, Jönsson says, faeces are considered impure and urine is viewed in a similar way, even though the hygiene risk associated with it is minimal.
Pradhan says that studies will be done to assess how acceptable the idea is in different cultures. His team will also investigate ways of decontaminating any faecal matter in urine collected from a toilet using a jerry can.
He adds: "For large-scale implementation of this idea, we are trying to find different methods to reduce the volume of the urine in economic way, without losing the nutrients".