What 2,000 Buried Underpants Revealed About Where Soil is Most Alive

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.

Gardens Beat Farms, and Both Beat Lawns in Soil Health

Land use was the single biggest factor determining how fast the underwear decomposed. Private gardens showed the highest breakdown rates, averaging around 58 percent decomposition after two months. Croplands fell in the middle at around 51 percent, permanent grasslands came in at roughly 47 percent, and lawns ranked last with an average of about 40 percent.

Private gardens also had the highest levels of soil organic carbon and available nutrients of any land type in the study, which likely explains their high biological activity. Arable farm fields, despite regular tilling and disruption, still outperformed lawns. Researchers suggest that physical disturbance from plowing can, in some cases, stimulate soil organisms. Lawns, on the other hand, are often mowed frequently, treated with herbicides, and planted with low-diversity grass, practices that can suppress the underground communities that drive decomposition, though the study could not pin the difference on any single lawn-management practice.

One finding that surprised researchers was how high nutrient levels were in private gardens compared to what plants actually need. Available phosphorus, a nutrient that plants require in controlled amounts, averaged more than 13 milligrams per kilogram of soil in private gardens. In arable fields, the average was around 3.5 milligrams per kilogram, well within recommended ranges. Some private garden soils exceeded 60 milligrams per kilogram. Plants can’t absorb all excess phosphorus, and it can run off into waterways, harming aquatic ecosystems and drinking water quality. In other words, some private gardens may be getting more fertilizer than their plants can use, even as their underwear decomposition scores looked excellent.

A Citizen Science Project That Delivered Real Data

Of the 1,100 participation packs mailed out, 883 soil samples, 1,752 pairs of underwear, and more than 7,000 tea bags were returned along with 800 completed questionnaires. After filtering for data quality, researchers included 780 sites in the final analysis. At least half of all participants were farmers, ensuring the dataset reflected real agricultural conditions across Switzerland.

Participants selected their own burial sites, dug holes of a standardized size, inserted two pairs of underwear vertically, and placed tea bags alongside them. After one month, they retrieved one pair along with some of the tea bags. After two months, they dug up the second pair and the remaining tea bags. Everything was air-dried and mailed back for laboratory analysis. A smartphone app let participants log their location, upload photos, and provide details about how their land was managed.

Results from the underwear matched up well with those from the more established tea bag method, giving researchers confidence that the Underpants Index measures something real. Both tools told a similar story about which soils were most biologically active.

Researchers are careful to note that the Underpants Index most strongly reflects soil fertility, meaning nutrient availability, rather than soil health in the fullest sense. A soil loaded with nutrients will break down cotton fast, but that does not automatically mean the soil is in good ecological condition. In natural ecosystems like meadows or forests, very high nutrient levels often signal human disturbance, not health, and can drive out rare plant species.

Researchers also showed that a simple visual rating scale, where someone estimates decomposition in 10 percent increments just by looking at the underwear, produced results nearly as accurate as the more involved computer-based image analysis. That means the method is genuinely accessible to anyone with a backyard and a spare pair of cotton briefs.

Soil forms the thin layer of earth that makes most life on land possible, yet it remains one of the least appreciated resources on the planet. Giving a thousand ordinary people a simple, memorable, and slightly absurd way to measure its health may be exactly the kind of unconventional thinking that gets more people to care about the ground that sustains them.

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