A thousand people from 25 countries buried their cotton underpants for two months. They did this not to keep the Underpants Gnomes from stealing them, but as part of a citizen‑science project that aimed to map soil health around the world. The results of this unusual experiment were published in the journal Plants People Planet.
“Our results show that how soil is managed can significantly affect both soil life and soil quality,” said co‑author Marcel van der Heijden, an agroecologist at the University of Zurich. “Healthy, biologically active soil is crucial for fertility, nutrient cycling and many other ecosystem services.”
Soil health matters for agriculture and for the planet. When soil is healthy, it keeps crops growing, it stores carbon, and it supports many other life‑supporting functions. Unfortunately, soil health has been declining worldwide, according to the authors. One way scientists measure soil health is by looking at how fast complex organic matter breaks down. This process turns leaves, wood, and even dead animals into simpler substances, releasing carbon dioxide and nutrients.
Large‑scale studies of decomposition are rare. Most work has been done on a small scale, but those studies show that how people use a piece of land can change the soil’s living community.
A common tool for measuring decomposition is the “teabag index” (TBI). Researchers bury small bags filled with tea leaves and then check how much of the bag has broken down after a set time. The TBI is useful, but it needs careful handling and special tools, like a fine‑scale balance. Van der Heijden and his team thought the TBI could be improved.
They decided to use a more playful material that many people already know: cotton. Prior research had shown that cotton strips can also be used to gauge decomposition. So the team asked volunteers to bury cotton underpants, then dig them up after a few weeks and record what happened.
“Slightly or heavily decomposed? The more active the soil organisms, the faster the cotton material decomposes.” – Priska Koller, Agroscope
The project was called “Proof by Underpants.” The authors recruited 1,000 volunteers, 240 of whom are listed as co‑authors on the paper. Each volunteer received an activity pack that included two pairs of organic cotton men’s underpants, 12 teabags, a sampling bag for soil, and detailed instructions.
The volunteers chose a spot in a field, meadow, or garden. They dug a hole, took a soil sample, and then placed the two pairs of underpants vertically, side by side, with the synthetic waistband visible on the surface. Six teabags were placed in front of each pair of underpants so that the volunteers could compare the cotton with the traditional teabag method.
After filling the hole, the volunteers waited 30 days and then dug up the first pair of underpants and the associated tea bags. They recorded the condition of the items and mailed everything back to the scientists. The second pair was removed after 60 days.
The biggest factor that affected how fast the underpants broke down was the type of land use. Underpants decomposed the fastest in private gardens. Those gardens also had the highest levels of organic matter, which creates a good environment for earthworms, fungi, and bacteria. Lawns showed the least activity of soil organisms. Agricultural fields and meadows fell in between.
Temperature and moisture also mattered. If the soil was too cold or too dry, decomposition slowed. Soil nutrient levels had a similar effect.
The authors concluded that the “underpants index” gave information about soil conditions that was as useful as the teabag index. It also measured chemical and physical properties, elevation, and moisture. Unlike the TBI, the underpants provided a direct visual and tactile measure of decomposition that is easier to interpret. The authors wrote that this makes it an ideal tool for citizen‑science projects and for raising awareness about soil issues.
“A selection of the more than 2,000 cotton underwear items in various stages of decomposition that were buried in fields, meadows, and gardens.” – Priska Koller, Agroscope
The study shows that soil health can be measured in a fun and engaging way. By turning a simple piece of clothing into a scientific tool, the project invited ordinary people to learn about the hidden life beneath their feet.
Plants People Planet, 2026. DOI: 10.1002/ppp3.70259
Healthy soil is the foundation of food security. When soil is rich in life, it can hold more water, release nutrients slowly, and resist erosion. The underpants experiment shows that even small changes in how we use land can have a big impact on soil health. It also shows that science can be made accessible to everyone.
The project demonstrates that citizen science can produce reliable data. The volunteers followed simple instructions, and the results matched what scientists would expect from more traditional methods. This opens the door for more projects that use everyday objects to study the environment.
The next time you see a pair of underpants, think about the soil beneath your feet. Soil health is not just a scientific concept; it is something that affects everyone. By participating in projects like Proof by Underpants, people can help protect the planet and learn about the living world that supports us all. ---
Plants People Planet, 2026. DOI: 10.1002/ppp3.70259