The Encyclopaedia Britannica tells us that a litre of typical male urine contains a gram of phosphate, one of the three major plant nutrients. Since most men urinate away up to 2.5 litres a day, that’s peeing a lot of P, the chemical symbol we know the nutrient by.
Phosphate is in great demand. It is especially short in tropical soils. Although an Irishman named James Murray invented the valuable fertilizer superphosphate in 1817 by treating bones with sulphuric acid the modern way is using mined calcium phosphate. Supplies are becoming limited, so scientists are searching for other, more reliable, sources.
The scientists found Swedish farmers were way ahead of them. Traditionally, they had been collecting urine stored at private homes and applying it to their fields. Over a decade ago, the Stockholm Water Company started researching large-scale use of urine on farm fields. New toilets that keep urine separate along with storage facilities have been developed.
”Urine is the most concentrated source of phosphorus,” says Professor Cynthia Mitchell, of the Institute for Sustainable Future at the University of Technology, Sydney, Australia. A limited trial is underway there in the northern state of Queensland.
In Finland, Surendra K. Pradham of the University of Kuopio and his colleagues grew cabbages using human urine that had been stored for six months, a recent issue of the weekly Science News tells us. The cabbages grew better and larger than using ordinary fertilizer or none at all, the scientists say. They also calculated that a year’s worth of one person’s pee could fertilize over 160 cabbages grown on a 90-square-metre plot.
Cumbers also grow better from the same urine fertilizing, the Finnish researchers showed
Since world deposits of phosphorus are due to run out in 50 years, according to Prof. Mitchell, such research could be very important. It could avoid war. Ancient bird droppings, called guano, are rich in phosphates. A principal source was from islands off the west of South America. In the late 19th century, Peru, Bolivia and Chile went to war over these islands. As a result, Bolivia lost its entire coastline.
Nitrogen and potassium are the other two major nutrients a plant cannot do without – N and K in scientific abbreviation. In fact that single litre of man’s urine also contains 10g of nitrogen and 2g of potassium. A typical artificial fertilizer known as NPK 20:20:20 bought from a store contains just a single gram of each. Worldwide, one billon people use flush toilets that are connected to sewage systems. That’s a lot of valuable fertilizer going down the drain.
