Cotton underpants used in Swiss citizen science project to measure soil health

Representative image

What happens when you bury a pair of cotton underpants in the ground and come back two months later? For nearly 1,000 citizen scientists in Switzerland, the answer offered an unusual window into the hidden world beneath their feet. In a large citizen science project, participants buried more than 2,000 pairs of cotton underpants and 12,000 tea bags at sites across Switzerland. The goal was not a prank. Researchers wanted to see whether the speed at which the cotton broke down could reveal how active the soil's living community was. The results, published on August 26 in New Phytologist Foundation, suggest that a simple pair of cotton underpants can provide useful clues about soil decomposition and fertility — while also helping people pay more attention to one of Earth's most important and often overlooked resources.

The more the underpants disappeared, the more active the soil was

Soil is filled with bacteria, fungi and other tiny organisms that break down organic matter. The researchers used cotton underpants as a simple way to observe this process. Participants buried two pairs at each site and dug them up after one and two months. The idea was simple: the more the cotton had decomposed, the more biologically active the soil was likely to be. After one month, the underpants had lost an average of about 10% of their material. After two months, average decomposition had reached more than 50%. The researchers called the measure the “Underpants Index” and compared it with the more established Tea Bag Index, which also measures how quickly organic material breaks down in soil.

Private gardens produced the biggest surprise

Where the underpants were buried made a major difference. Private gardens showed the highest average decomposition after two months, with around 58% of the material breaking down. Lawns showed the lowest rate at around 40%, while farmland and grasslands fell somewhere in between. Land use was the strongest factor affecting decomposition, the researchers found. Soil nutrients and other soil properties also played a role. The findings suggest that the underpants test may reflect soil fertility and biological decomposition activity more strongly than soil health in its broadest sense. That distinction matters because faster decomposition is not always a sign that a natural ecosystem is healthier.

Why scientists chose underpants instead of expensive equipment

The unusual experiment had another purpose: making soil science easier for ordinary people to understand. Testing soil can require specialised equipment and technical knowledge. A buried pair of cotton underpants, however, offers a visual result that almost anyone can understand. Participants could simply see how much of the fabric had disappeared. The project also showed the power of citizen science. Around 1,000 people helped researchers collect data from hundreds of locations — a scale that would have been difficult for a small research team to achieve alone. The researchers say the method is not a complete test of soil health. But it can offer a simple first look at what is happening below the surface and help people understand that soil is far more than just dirt. After all, for this experiment, the condition of a pair of buried underpants helped tell a much bigger story about the living world beneath our feet.