GoKawiilAfter being buried in the ground for two months and broken down by soil organisms, a new pair of cotton underwear (left) shows clear signs of decomposition (right). (Credit: Nicolas Zonvi)
In a Nutshell Private gardens had the highest soil biological activity of any land type studied, while lawns had the lowest.
How much underwear decomposed was strongly linked to how many nutrients and how much organic material were in the soil.
Burying cotton underwear proved to be a simple, easy-to-use way to get a first impression of soil biological activity that anyone can try with a comparable pair of cotton briefs.
Bury a fresh pair of cotton briefs, wait two months, and the holes tell the story. A shredded pair means the soil below is alive and working. A pair that comes back nearly whole means the ground is barely stirring. That simple test is behind one of the more unconventional environmental studies in recent years, and it actually delivered hard data on soil health across an entire country.
Researchers recruited approximately 1,000 citizen scientists to bury more than 2,000 pairs of organic cotton underwear and 12,000 tea bags at 1,000 locations across Switzerland. After one and two months underground, participants dug up the garments and sent them back to a research team at Agroscope, a Swiss agricultural research institute. The amount of each pair eaten away by soil organisms measured how biologically active and fertile that soil was. More decomposition meant a livelier underground ecosystem. Less decomposition pointed to lower biological activity.
Quirky as the method sounds, the findings carry real weight. Soils worldwide are quietly degrading, threatening food supplies, clean water, and the biodiversity that keeps ecosystems running. Yet the general public pays little attention to what happens beneath their feet. This project, launched under the name “Proof by underpants” and published in the journal Plants, People, Planet, was designed to change that, attracting media coverage in more than 25 countries while simultaneously collecting hard scientific data on soil health at a national scale.
Why Cotton Underwear Is a Surprisingly Good Soil Health Test
Cotton is made almost entirely of cellulose, a natural plant fiber that soil organisms are well-equipped to break down. When soil is teeming with bacteria, fungi, and other tiny living things, cotton fabric disappears relatively quickly. When the soil community is weak or struggling, the fabric holds together much longer. Researchers have used cotton strips and specialty tea bags for similar purposes before, but those methods require precise scales and careful handling. A pair of underwear, by contrast, offers something immediate: anyone can look at what came out of the ground and grasp what it means.
After participants retrieved the undergarments, the research team spread each pair flat, photographed them against a blue background, and used imaging software to calculate exactly how much of the original fabric remained. That number became what the researchers call the “Underpants Index,” a straightforward score for soil biological activity. On average, about 10 percent of each pair had broken down after one month. By the two-month mark, that figure jumped to roughly 50 percent, though results varied widely depending on where the underwear was buried.
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