Urine was used as fertiliser in ancient Rome and China. Now farmers in Vermont are bringing this practice back to boost harvests and grow crops in a more sustainable way.

Williams takes part in the Urine Nutrient Reclamation Program (UNRP), a programme run by the Rich Earth Institute (REI), a non-profit based in Vermont. She and 250 of her neighbours in Windham County donate a total of 12,000 gallons (45,400 litres) of urine to the programme each year to be recycled – or “peecycled”.

Windham County’s pee-donations are collected by a lorry and driven to a large tank where the urine is pasteurised by heating it to 80C (176F) for 90 seconds. It is then stored in a pasteurised tank, ready to be sprayed on local farmland when the time is right to fertilise crops.

Records suggest that urine was used to help grow crops back in ancient China and ancient Rome. Today, scientists are finding that it can more than double the yield of crops like kale and spinach compared to no fertiliser, and improve yields even in low fertility soils.

Urine’s power as a fertiliser is due to the nitrogen and phosphorus that it contains – the same nutrients that are added to the synthetic fertilisers used on many conventional farms. But these synthetic fertilisers come at an environmental cost. Nitrogen is produced using the fossil fuel-intensive Haber-Bosch process, and the mining of phosphorus creates harmful amounts of toxic waste. Urine, meanwhile, is freely available – as Williams puts it, “everybody pees. [It’s an] untapped resource”.