To find out where Switzerland's soil is most biologically alive, researchers didn't reach for a microscope first — they reached for underwear. Over two years, roughly 1,000 volunteers buried more than 2,000 pairs of plain cotton underpants, along with 12,000 tea bags, at about 1,000 sites across the country, then dug them back up to see how much the soil had eaten.
An Index Made of Underpants
The project, run by the University of Zurich and the federal agricultural research institute Agroscope and nicknamed "Proof by Underpants", relies on a decades-old trick among soil scientists: cotton fabric is broken down by the same microbes, fungi and invertebrates that cycle nutrients through soil, so the speed of decomposition is a rough but genuine measure of how biologically active a patch of ground is. Tea bags, which decompose at more predictable rates, were buried alongside the underwear as a calibration check.
Participants followed a standardized protocol — burying the items at a set depth, waiting two months, then digging them up, photographing the results and mailing samples to a lab along with a soil sample of their own. Around 240 of the volunteers ended up credited as co-authors on the resulting paper, a scale of public participation the researchers say would have been unaffordable through a conventional study.
The results, described this month, point to land use as the single strongest predictor of how alive the soil underneath actually is — a stronger factor than the physical and chemical soil properties the team also measured. Private gardens showed the fastest decomposition and the highest biological activity, tended soil in backyards apparently rich enough in organic matter and undisturbed enough to host a thriving underground community. Lawns fared worst, with agricultural fields and meadows landing in between.
The researchers, co-led by Marcel van der Heijden and Franz Bender, are now proposing the buried-underwear method as a low-cost "underwear index" that citizen scientists, schools or municipalities could use to track soil health over time, without needing a laboratory budget. Given how central soil biology is to everything from crop yields to carbon storage, the team argues that a rotting pair of underpants may be one of the more honest report cards available — see additional coverage from ScienceAlert on how the method was calibrated.
