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In South America, for at least 1500 years, the local people were rowing to offshore islands to collect guano (accumulated seabird poo) to use as fertiliser. Guano is unusually rich in phosphate, potassium and nitrogen and the people who wanted it for their crops had developed methods for harvesting, transporting, and distributing guano sustainably.
In 1802, the German naturalist and explorer Alexander von Humboldt, came across this use of guano, which led to the development of a global trade that included shipping thousands of Chinese labourers to Peru and Chile to obtain guano for shipment to Europe. This mass extraction, as well as discounting the rights of local people, destroyed the supply of guano within a few decades.
In the 1840s, Reverend John Stevens Henslow discovered abundant coprolites, the fossilised faeces of dinosaurs, near Felixstowe in Sussex. He extracted the phosphate by treating the coprolites with sulphuric acid, starting the coprolite mining rush of the 1860s but, just like the guano, the supply quickly ran out.
In ancient Egypt cats were reared specifically to be slaughtered for mummification to keep people company in the afterlife. The mass reared animals were strangled at six months old, tightly bound and dried and sold to those wishing to curry favour with the gods. Thousands of years later, in 1888, an Egyptian farmer discovered a tunnel packed with hundreds of thousands of mummified cats, which he crushed up and used as fertiliser. Soon boatloads were exported to Liverpool to be sold at auction. British farmers had turned to powdered cats for their phosphates!
For thousands of years the main source of potassium-rich fertilisers (potash) was wood ash, leading to vast forest clearance as the felled trees were burned.
Today phosphate fertiliser is extracted from phosphate-rich rocks, another non-renewable source. The one renewable source that farmers used for millennia was manure and composted crop waste.
Next time in this column, I will look at the history of nitrogen fertilisers and the rising cost of synthetic nitrogen fertilisers – while a solution may well be on the horizon.
