Why Scientists Had 1,000 Volunteers Bury Their Underwear

A national science project in Switzerland turned a surprisingly ordinary item of clothing into a tool for studying life beneath the ground: cotton underwear. Researchers from the University of Zurich and Agroscope launched the citizen-science project “Proof by Underpants” in 2021. More than 1,000 volunteers buried over 2,000 pairs of cotton underwear and 12,000 tea bags at roughly 1,000 sites across the country. After two months, participants dug up the items, photographed them and submitted them to laboratories along with soil samples. The researchers used the condition of the underwear as a simple indicator of underground biological activity. Soil organisms break down cotton, so faster decomposition suggested more activity beneath the surface. The results, reported in the journal Plants, People, Planet, showed marked differences between land types. Underwear decomposed most quickly in private gardens, where researchers also found the highest levels of organic matter. Lawns had the slowest decomposition, while agricultural fields and meadows fell between the two. According to the researchers, land use had a stronger influence on decomposition speed than most of the other soil characteristics they measured. Nutrient levels also affected soil activity. Conditions such as temperature and moisture mattered as well: soil organisms became much less active when the ground was especially cold or dry. The findings do not mean that the fastest decomposition is always the best outcome. Rapid breakdown was often linked with fertile, nutrient-rich soil, which can benefit agricultural production. But the researchers said excessive nutrient levels in forests or gardens may signal a disruption or oversupply, including from too much fertilizer. The project was intended not only to collect data but also to draw attention to soil ecosystems. The University of Zurich said soil supports food production, stores water, carbon and nutrients, and provides habitat for a large share of life on Earth. The researchers proposed that an “underwear index” could make soil processes easier for the public to understand. The large volunteer effort also produced one of Switzerland’s most comprehensive datasets on soil life, according to the source material. About 240 citizen scientists were listed as co-authors of the resulting study, and participants received soil-analysis results and advice on more sustainable soil management.