Gardening – Fertiliser gets down and dirty

The first fertiliser produced by chemical processes was ordinary super phosphate made in the early 19th century by treating bones with sulphuric acid.

Plant available nitrogen (nitrate) is scarce and for most of agriculture’s history, farmers cycled usable nitrogen back into the soil through human and animal manure and composting crop waste. For example, in the early 1700s in Osaka Japan, neighbouring villages fought over the rights to city residents’ poo to use as fertiliser!

In 1909 the German chemist Fitz Harber (1868-1934) considered the father of chemical warfare, discovered that the chemical reaction of nitrogen and hydrogen produced ammonia, the main component of nitrogen-based fertilisers. In conjunction with Carl Bosch he invented a machine that could handle the high temperatures and pressures necessary for production. This breakthrough, using fossil fuels, enabled the mass production of agriculture fertilisers and today the process manufactures virtually all the world’s supply. One hundred tonnes of nitrogen are taken from air every year and converted to ammonia components in the Harber-Bosch factories. It is estimated that half the nitrogen atoms in our bodies come from a Harber factory via the fertilisers and food grown by industrial agriculture.

Soon after the factory was built, WWI began and it was used to manufacture explosives, develop a new weapon (chlorine gas) and the pesticide Zyklon B, which was used by the Nazis in the concentration camps.

Synthetic nitrogen fertilisers are explosive and today are a major component in bombs made by terrorists.

In today’s changing climate, many scientists are worried about the serious imbalance to the nitrogen cycles and believe the impact will be greater than the imbalance in the carbon cycle.

Statistics tell us we are deep in the poo – an average person produces about 181kg of the stuff annually. With the soaring price of synthetic fertilisers, wars, supply chain interruptions and ecological concerns, companies are looking seriously at the potential of turning human waste into fertiliser.

In her new book, The Other Dark Matter -The Science and Business of Turning Waste into Wealth and Health, Linda Zeldovich profiles two extremely successful options – Washington DC’s sewage treatment plant processes the contributions of 2.2 million people into Grade A fertiliser that is sold in stores. And, in the Pacific Northwest, scientists are working to turn Vancouver’s cheap and abundant sewer sludge into biofuel – essentially poo-derived gas.