By burying thousands of pairs of cotton underwear across Switzerland, scientists uncovered striking differences in biological activity from one type of land to another.
The results showed that gardens had especially active soils, while lawns were much quieter underground.
Soil supports the global food system while also storing water, carbon, and essential nutrients. It is also one of the planet’s richest habitats. Scientists estimate that more than half of Earth’s biodiversity lives below the surface. But as biodiversity declines worldwide, soil health is also deteriorating, creating risks for agriculture, food security, and the stability of entire ecosystems.
In 2021, researchers at the University of Zurich (UZH) and Agroscope, the Swiss federal center of excellence for agricultural research, launched a citizen science project called Proof by Underpants (Beweisstück Unterhose). The goal was to make the hidden world beneath our feet more visible while gathering scientific data at a large scale.
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 locations across Switzerland. After two months, participants dug them back up, photographed them, and sent them to a laboratory along with soil samples for additional analysis.
Decomposition Reveals Soil Activity
The findings, which produced a map of biological activity in Swiss soils, have now been published in Plants, People, Planet. Researchers found that the underwear broke down at very different rates depending on where it had been buried.
That variation offered a useful measure of biological activity. Where soil organisms were more active, they decomposed the cotton more quickly.
Private gardens had the fastest rates of decomposition. These soils also contained the highest amounts of organic matter, creating favorable conditions for earthworms, fungi, bacteria, and other organisms that live underground. Lawns showed the lowest biological activity, while meadows and agricultural fields generally fell between the two extremes.
Land Use Strongly Shapes Soil Health
“Our results show that how soil is managed can significantly affect both soil life and soil quality,” says co-study leader Marcel van der Heijden, UZH professor of agroecology. “Healthy, biologically active soil is crucial for fertility, nutrient cycling and many other ecosystem services.”
Practices that can support soil life include keeping the ground permanently covered, adding compost, using more diverse crop rotations and reducing the use of mineral fertilizers and pesticides.
Among all the factors examined, land use had the strongest influence on how quickly the underwear decomposed. Whether a location was a garden, meadow, cultivated field, or lawn explained the differences better than most of the soil properties the researchers measured. Chemical characteristics, including nutrient levels, also had an important effect.
Faster Breakdown Can Also Signal Excess Nutrients
Rapid decomposition was often associated with fertile soil and a strong supply of nutrients, which can be especially valuable in agriculture. But faster decomposition is not always desirable.
“However, maximum decomposition is not desirable in every ecosystem,” says co-project leader Franz Bender, head of the agroecological assessments team at Agroscope.
“In near-natural habitats such as forests, very high nutrient levels can indicate disruptions to the natural balance of nutrients. In gardens, too, rapid decomposition of the underwear may point to an oversupply of nutrients,” says Bender.
In those situations, reducing fertilizer use may be worth considering. Temperature and moisture also strongly influence soil organisms. When soils become too cold or too dry, biological activity drops sharply.
An “Underwear Index” for Soil Health
The study suggests that burying cotton underwear could provide a simple and meaningful way to highlight differences in soil fertility and biological activity.
Researchers therefore propose an “underwear index” as an easy way to visualize what is happening underground and help the public better understand why protecting healthy soils matters.
Citizen Scientists Make Large-Scale Research Possible
The “Proof by Underpants” project also highlights the value of citizen science. A study covering around 1,000 locations would have been difficult to carry out without the participation of volunteers.
The resulting data span every region of Switzerland and make up one of the country’s most comprehensive datasets on soil life. The scale of public involvement is also reflected in the study’s authorship, with around 240 citizen scientists listed as co-authors.
In return, participants received individualized feedback from the researchers, including soil analysis results, assessment tools, and recommendations for more sustainable soil management.
Reference: “Soil health assessment using buried cotton underpants with the help of 1000 citizen scientists” by S. Franz Bender, Diane Bürge, Luca Bragazza, Eva Knop, Sandie Masson, Noemi Peter, Romina Demarmels, Daniel Mueller, Ariane Imhof, Pia Viviani, Atlant Bieri, Frank Liebisch, Stefan Geisen, Yann Hautier, Panos Panagos, Pablo Garcia-Palacios, Marta Goberna, David Johnson, Simon Jöhr, Alain Valzano-Held, Claudia Weik, Nadine Gloor, Heidi Aguilar, Marco Agustoni, Barbara Albertoni, Regina Anderson, Alberto Andreani, Bénédicte Arguillère, Osvaldo Arrigo, Barbara Auer, Vanessa Badà, Brigitte Baenteli, Gaëlle Balleys, Dagmar Bay, Daniel Beck, Martina Becker, Alma Bender-Freisinger, Sarah Benoit, Barbara Bernasconi, Chiara Bernasconi, Marco Bertschinger, Michael Bessard, David Bichsel, David Bichsel, Matteo Binda, Joel Bischof, Ruth Bischof, Bernadette Bisig, Andreas Bitterli, Natacha Bodenhausen, Yann Bonjour, Lucien Bovy, Tanja Boyandin, Eliane Breitenmoser, Christian Brönimann, Nathalie Brückner, Marcel Bucher, Stefan Bucher, Andreas Cadonau, Simone Cairoli, Elodie Calais, Bruno Campana, Catrina Canetta Collenberg, Davide Carrara, Cristian Cattaneo, Ester-Camilla Cattaneo, Renzo Cattori, Silvana Cavagna, Luciano-Grazia Cavallini, Elio Cavargna, Laura Cerri, Marlis Chanton, Camilla Chiesa, Elisabeth Clément, Morgane Clivaz-Duc, Léonie Cocquio, Helio Correia, Cristina Corti, Stefano Corti, …, Anita Zulliger, Renatus C. Zürcher, Thomas D. Bucheli and Marcel G. A. van der Heijden, 26 August 2026, Plants, People, Planet.
DOI: 10.1002/ppp3.70259
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