"Please Bury Your Underwear": What Happened? The Truth Uncovered by a Bizarre Project

Five years ago, Swiss scientists made a strange request to citizens: "Please bury cotton underpants in the ground." It was not just a pair or two. A total of 1,000 citizens buried more than 2,000 pairs of underpants across Switzerland. When they dug them up two months later, some remained almost intact, while others were decomposed beyond recognition. What on earth happened underground?

1. Why Underpants, of All Things?

The experiment began in 2021 when the University of Zurich and Agroscope, the Swiss federal agricultural research institute, launched a uniquely named project: "Proof by Underpants."
Across the country, 1,000 citizens participated by burying cotton underpants and tea bags according to designated guidelines in land around them, such as gardens, agricultural fields, and grasslands. Two months later, they dug up the underpants, photographed them, and sent them back to the researchers along with soil samples. Why underpants, of all things? What researchers actually wanted was not the underpants themselves, but cotton. They sought to observe how much cellulose, the primary component of cotton, decomposes.

Choosing underpants served both to attract public interest and to fulfill a practical purpose. Plain cotton swatches might disappear entirely and become difficult to locate after heavy decomposition, but with underpants, the elastic waistband and synthetic seams remain even if the cotton fabric dissolves away. This allowed participants to visually confirm the extent of decomposition and retrieve the buried items.

2. Who Ate the Underwear?

It may look like ordinary soil, but peering inside reveals an entirely different world.
Researchers at the University of Zurich estimate that more than half of the world's biodiversity exists beneath the ground. These organisms break down organic matter such as dead plants and fallen leaves, transforming them back into nutrients that plants can utilize. To them, cotton underpants were also organic matter to be decomposed. If identical underpants buried for the same duration saw one pair almost disappear while the other remained relatively intact, it indicates that soil biological activity differed between the two plots.
An interim analysis in 2022 also confirmed that organic matter plays a vital role. The researchers did not rely merely on visual estimation.
They laid out the decomposed underpants against a blue background, photographed them, and calculated precisely how much surface area had degraded using an image analysis program.

3. Digging Up 2,000 Pairs Across the Nation

After five years of analysis, the final findings were published in August in the international journal 'Plants, People, Planet.' The factor that most significantly influenced the degree of decomposition was how the land was used—in other words, land use practices. The fastest decomposition occurred in private gardens. Rich in organic matter and nutrients, they provided an ideal environment for soil organisms to thrive. Conversely, biological activity was lowest in lawns. Agricultural fields and grasslands fell somewhere in between. Despite using the same underpants, the outcome varied depending on where they were buried.

The research team took this a step further: Could the decomposition rate of underpants serve as a simple metric to assess soil conditions without complex equipment?
Researchers presented this concept as the "underwear index." By burying identical cotton underpants, digging them up, and evaluating their degradation, anyone can intuitively verify the invisible activity of underground organisms.

4. Does More Rot Mean Better Soil?

Does that mean the soil where underpants disappear the fastest is the best soil? Not necessarily. Temperature and moisture also affect the rate of decomposition. If it is too cold or dry, the activity of soil organisms decreases significantly. Excessive nutrients can also accelerate decomposition. In ecosystems close to a natural state, such as forests, an overabundance of nutrients can actually signal a disrupted natural balance. The same applies to private gardens. If underpants decomposed extremely quickly, researchers note that one should check whether fertilizers are being overused.

Thus, the simplistic formula "more decomposed underpants = unconditionally healthy soil" does not hold. Rather than serving as an absolute score of soil health, the underwear index functions as an accessible indicator that allows people to easily look into how actively subterranean creatures are moving and gauge the condition of the soil.

5. From Underwear to Drought

The underwear-burying experiment brought another unexpected issue to light: drought. In the interim analysis released in 2022, the humus content in agricultural soil was on average 23% lower than in private gardens. Soils with higher humus content not only decomposed underpants faster, but they could also retain more water. Soil rich in organic matter served as a hospitable environment for soil organisms while simultaneously possessing a superior capacity to retain water.

As climate change makes droughts more frequent, how well crops can withstand dry spells ultimately links to how effectively the ground can hold moisture. An experiment that began with burying underpants ended up connecting directly to the crops we eat and broader climate change challenges.

6. How to Cultivate Good Soil

How, then, can we build an environment where underground organisms thrive? In their final study, the researchers suggested several methods: keeping the ground continuously covered with plants or mulch to prevent direct exposure, supplying organic material such as compost, and rotating various crops rather than relying on continuous monoculture. Restricting the use of mineral fertilizers and chemical pesticides was also proposed as a way to stimulate soil biological activity.

7. What a Few Scientists Could Not Do, 1,000 Citizens Did

In this experiment, there was something just as vital as the underpants: the people who buried them. For a research team, traveling to 1,000 locations across Switzerland to dig holes, bury underpants, and return two months later to unearth them all would have been practically impossible. Yet when citizens were asked, "Please bury underpants," 1,000 people stepped up.
Data was gathered across Switzerland from gardens, grasslands, and agricultural plots, resulting in one of the most comprehensive datasets on Swiss soil biological activity.

A glance at the final paper's author list reveals an extraordinary sight: 240 citizens were credited as co-authors of the scientific paper. Ordinary citizens who buried and dug up underpants two months later became co-authors of an academic paper five years down the road. The researchers, in turn, provided participants with individual soil analysis results and practical advice on managing their soil sustainably. Scientists gained data they could never have collected alone, and citizens received scientific analyses of the land beneath their feet. It was a prime example of "citizen science," where scientists and citizens collaborated to produce scientific data.

8. What the Underpants Ultimately Showed

The beginning seemed somewhat comical: burying 2,000 pairs of underpants in the ground. Yet following the process of their disappearance gradually brought unseen elements to light—bacteria, fungi, earthworms, and countless soil creatures, the organic matter cycles they drive, moisture-retaining soil, and the crops growing above that nourish us.
In the end, what the scientists wanted to observe from the start was not underwear. It was the ecosystem beneath our feet, which we tread upon every day but seldom pause to inspect.


Deep Dive Q&A
Q1. Why did Swiss researchers conduct the experiment by burying 'cotton underpants' instead of ordinary fabric swatches?

A1. The goal was to measure how much cellulose, the primary component of cotton, is decomposed by soil organisms. Ordinary cotton swatches leave no trace when broken down by soil microbes and earthworms, making them difficult to locate in the ground. In contrast, with cotton underpants, only the cotton fabric decomposes while the elastic waistband and synthetic stitching remain, allowing researchers to relocate the buried item and easily observe the extent of decomposition with the naked eye. Additionally, it carried the practical intent of piquing public curiosity to mobilize the participation of 1,000 citizens.

Q2. Can soil where underpants decompose and disappear the most be considered unconditionally the healthiest soil?

A2. Not necessarily. Aside from the vitality of soil organisms, factors such as temperature, moisture, and nutrient levels interactively influence the rate of underwear decomposition. Especially in forests or natural ecosystems, an excessively rapid rate of decomposition may indicate that an oversupply of nutrients has disrupted the natural balance. Therefore, the simplistic formula "more decomposed underpants = unconditionally healthy soil" does not apply, and the 'underwear index' should be interpreted as a reference indicator to intuitively observe the activity of subterranean organisms and the overall condition of the soil.
※ Please note: This article was translated by AI and may contain errors.