Fez — Scientists have buried more than 2,000 pairs of cotton underwear across Switzerland to investigate how active the organisms living beneath the soil really are.
In 2021, researchers from the University of Zurich and Agroscope, Switzerland’s federal agricultural research center, recruited 1,000 volunteers for the “Proof by Underpants” project. Participants buried underwear and tea bags at around 1,000 locations before retrieving them two months later.
The volunteers photographed the decomposing garments and sent them to researchers alongside soil samples. The resulting study, published in “Plants, People, Planet,” used the rate of decomposition as a measure of biological activity in the soil.
What underwear can reveal about soil
The idea behind the experiment is straightforward. Soil organisms such as bacteria and fungi break down organic material, including cotton. The faster they decompose the fabric, the more biologically active the soil is likely to be.
The researchers developed an “Underpants Index” based on the percentage of each garment that disappeared during the experiment. After one month, the underwear had decomposed by about 10% on average. After two months, that figure reached roughly 50%.
The scientists also buried 12,000 tea bags to compare the underwear method with an established technique for measuring decomposition.
The results showed major differences between locations. Land use emerged as the strongest factor influencing how quickly the underwear decomposed, followed by soil chemical characteristics.
Gardens came out on top
Private gardens recorded the highest biological activity, while lawns recorded the lowest. Croplands and grasslands fell between the two categories, according to the study.
The researchers also linked decomposition rates to soil nutrients, fertilizer use, soil texture, moisture, and temperature.
Yet faster decomposition does not necessarily mean healthier soil in every environment. High biological activity can accompany high fertility, but excessive nutrients can also disrupt natural ecosystems.
Franz Bender, co-project leader and head of the agroecological assessments team at Agroscope, cautioned that maximum decomposition is not desirable everywhere. In forests and other near-natural environments, unusually high nutrient levels can indicate a disruption to the natural balance.
A serious experiment with an unusual hook
Beyond the underwear itself, the project demonstrated how citizen science can expand environmental research.
The 1,000 volunteers generated data from around 1,000 sites across Switzerland, creating what researchers describe as one of the country’s most comprehensive datasets on soil life. Around 240 citizen scientists are also listed as co-authors of the resulting paper.
The researchers argue that underwear offers an accessible way to demonstrate processes that normally remain invisible. Anyone can see whether a cotton garment has largely survived underground or has been broken down by the organisms living in the soil.
That visibility is important because soil supports food production, stores water, carbon, and nutrients, and provides a habitat for a significant share of global biodiversity. Declining soil biodiversity can therefore affect agriculture, food security, and wider ecosystems.
The Swiss experiment ultimately turns a deliberately strange idea into a practical lesson. Beneath seemingly ordinary lawns, gardens, and fields, complex biological communities are constantly breaking down organic matter and recycling nutrients. Sometimes, researchers need little more than a shovel and a pair of underwear to show just how much is happening beneath our feet.
