Scientists Buried 2,000 Pairs of Underwear Across Switzerland to Measure Soil Health

Scientists in Switzerland buried more than 2,000 pairs of cotton underwear across the country and found striking differences in how quickly soil organisms broke them down — a simple test that revealed which types of land have the most biologically active soil. Gardens turned out to have the busiest soils, while lawns were the quietest underground.

The citizen-science project, called "Proof by Underpants," was launched in 2021 by researchers at the University of Zurich (UZH) and Agroscope, Switzerland's federal centre for agricultural research. Using a standardised method, 1,000 volunteers buried more than 2,000 pairs of cotton underwear and 12,000 tea bags at roughly 1,000 locations across the country. After two months, participants dug the items back up, photographed them, and sent them to a lab along with soil samples. The findings were published in the journal Plants, People, Planet.

The underwear decomposed at very different rates depending on where it was buried, giving researchers a simple measure of biological activity: the more active the soil organisms, the faster they broke down the cotton. Private gardens had the fastest decomposition and the highest organic matter, favouring earthworms, fungi, bacteria and other underground life. Lawns showed the lowest biological activity, with meadows and farmland falling in between. Land use had a stronger influence on decomposition speed than most of the soil properties the researchers measured.

"Our results show that how soil is managed can significantly affect both soil life and soil quality," said Marcel van der Heijden, a UZH professor of agroecology and co-leader of the study. He said practices such as keeping the ground covered, adding compost, using more diverse crop rotations, and cutting back on mineral fertilisers and pesticides can support soil life. Temperature and moisture also strongly affect soil organisms — activity drops sharply when soil becomes too cold or too dry.

Fast decomposition usually signals fertile, nutrient-rich soil, which is valuable for farming, but co-project leader Franz Bender of Agroscope said it is not always a good sign: in forests and other near-natural habitats, or in gardens, unusually rapid decomposition can point to an oversupply of nutrients, in which case cutting back on fertiliser may be worth considering. The researchers propose an "underwear index" as a simple way to visualise soil health, with around 240 citizen scientists credited as co-authors of the study.