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

Researchers from the University of Zurich and Agroscope, Switzerland's federal agricultural research centre, launched a citizen-science project called "Proof by Underpants" to study the hidden world of soil life, which scientists estimate holds more than half of all biodiversity on Earth. Using the same standardized method, 1,000 volunteers buried more than 2,000 pairs of cotton underwear and 12,000 tea bags at roughly 1,000 sites across the country in 2021. After two months, participants dug the material up, photographed it, and sent it along with soil samples to the laboratory.

How quickly the cotton underwear broke down served as a simple indicator of biological activity underground: more active soil organisms broke the cotton down faster. The findings, published in the journal Plants, People, Planet, showed that private gardens had the fastest decomposition and the highest levels of organic matter, favouring earthworms, fungi and bacteria. Lawns showed the lowest activity, with farm fields and meadows in between.

Land use had the strongest influence on decomposition speed of any factor the researchers measured, more than most soil chemical properties. Marcel van der Heijden, a University of Zurich professor of agroecology who co-led the study, said healthy, biologically active soil is crucial for fertility and nutrient cycling. He said practices such as keeping soil covered, applying compost, rotating crops and reducing fertiliser and pesticide use can support soil life.

The researchers cautioned that faster decomposition is not always better. While it often signals fertile soil useful for farmland, very high nutrient levels in near-natural habitats such as forests can indicate a disrupted nutrient balance, and in gardens it may point to over-fertilising. About 240 citizen scientists are listed as co-authors of the published study, which the researchers say produced one of Switzerland's most comprehensive datasets on soil life.