Bury a pair of fresh cotton underpants, wait two months, and the holes will tell the whole story. Shredded underwear indicates that the soil beneath is alive and functioning. Underwear dug up almost intact suggests the soil is largely inactive. This simple test lies at the heart of one of the most unconventional environmental studies in recent years, and it has actually yielded reliable data on soil health across the country.
Researchers enlisted about 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. One and two months after burial, participants dug up the garments and sent them back to the research team at Agroscope, the Swiss agricultural research institute. The amount of underwear material decomposed in the soil served as a measure of biological activity and soil fertility. The greater the decomposition, the more active the underground ecosystem; the less decomposition, the lower the biological activity.
As unusual as this method may seem, the results carry real weight. Soils worldwide are quietly degrading, threatening food supplies, clean water, and the biodiversity that sustains ecosystem function. Yet, the general public pays little attention to what is happening beneath their feet. Launched under the title “Proof in the Pants” and published in the journal Plants, People, Planet, this project aimed to change that—garnering media attention in over 25 countries while simultaneously gathering reliable scientific data on soil health on a national scale. Cotton consists almost entirely of cellulose, a natural plant fiber that soil organisms are adept at breaking down. When the soil teems with bacteria, fungi, and other small organisms, cotton fabric disappears relatively quickly. When the soil community is weakened or in poor health, the fabric persists much longer. Researchers have previously used cotton strips and specialized tea bags for similar purposes, but those methods require precision scales and careful handling. A pair of underpants, by contrast, offers something more immediate: anyone can look at what has been dug up and understand what it signifies.
After study participants retrieved the underwear, the research team laid each pair out on a flat surface, photographed them against a blue background, and used image-processing software to precisely calculate how much of the original fabric remained. This figure became what researchers call the “underwear index”—a simple indicator of soil biological activity. On average, about 10 percent of each pair had decomposed after one month. By the two-month mark, that figure had jumped to approximately 50 percent, though results varied significantly depending on where the underwear had been buried.
Land use had the greatest impact on the rate of underwear decomposition. Private gardens showed the highest decomposition rates, averaging around 58 percent over two months. On arable land, the figure was about 51 percent; on permanent grasslands, it was roughly 47 percent; and lawns ranked last, with an average of about 40 percent.
Private gardens also recorded the highest levels of soil organic carbon and available nutrients among all the land types in the study, which likely explains their high biological activity. Despite regular plowing and soil disturbance, arable fields actually showed better results than lawns. Researchers hypothesize that the physical impact of plowing may, in some cases, stimulate soil organisms. Lawns, on the other hand, are frequently mowed, treated with herbicides, and planted with low-growing grasses—practices that may suppress the underground communities responsible for decomposing organic matter, although the study could not pinpoint exactly which specific lawn-maintenance method was responsible for the observed effects.
One unexpected finding was the high nutrient content in private gardens relative to the plants’ actual needs. Levels of available phosphorus—a nutrient plants require only in controlled amounts—averaged over 13 milligrams per kilogram of soil in private gardens. In arable fields, this figure was around 3.5 milligrams per kilogram, which falls within recommended limits. In some private gardens, phosphorus levels exceeded 60 milligrams per kilogram. Plants cannot absorb all the excess phosph …and it can run off into bodies of water, harming aquatic ecosystems and drinking water quality. In other words, some private gardens may receive more fertilizer than their plants can absorb, even though the decomposition rates of their underwear look excellent.
Of the 1,100 kits sent out, participants returned 883 soil samples, 1,752 pairs of underwear, and over 7,000 tea bags, along with 800 completed questionnaires. After verifying data quality, the researchers included 780 sites in the final analysis. At least half of all participants were farmers, ensuring the dataset reflected real-world agricultural conditions across Switzerland.
Participants selected their own burial sites, dug standard-sized holes, inserted two pairs of underwear vertically, and placed tea bags alongside them. After one month, they retrieved one pair along with several tea bags. After two months, they dug up the second pair and the remaining tea bags. All items were air-dried and sent back for laboratory analysis. A smartphone app allowed participants to log their location, upload photos, and provide detailed information about their land management practices.
The results obtained using the underwear analysis aligned well with those from the more common tea bag method, giving researchers confidence that the Underwear Index measures something real. Both tools yielded similar results regarding which soils are the most biologically active.
The researchers emphasize that the “Underpants Index” primarily reflects soil fertility—specifically nutrient availability—rather than soil health in the full sense of the term. Nutrient-rich soil breaks down cotton quickly, but this does not automatically mean the soil is in good ecological condition. In natural ecosystems like grasslands or forests, very high nutrient levels often indicate human interference rather than health, and can lead to the loss of rare plant species.
The researchers also demonstrated that a simple visual rating scale—where a person estimates the degree of decomposition in 10 percent increments just by looking at the underwear—yields results almost as accurate as more complex computer-based image analysis. This means the method is truly accessible to anyone with a backyard and a spare pair of cotton underpants.
Soil forms the thin layer of earth that sustains most life on land, yet it remains one of the planet’s most undervalued resources. Offering a thousand ordinary people a simple, memorable, and slightly absurd way to assess its condition might be just the unconventional approach needed to get more people to care about the land that nourishes them.
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