Two thousand white underwear, 12 thousand tea bags and a shovel. In 2021, a thousand people scattered across Switzerland received this unusual scientific kit, buried everything and waited for the soil to do its job. After two months, on average about 50% of the cotton underwear had disappeared. Some were torn to shreds, others decidedly more presentable. Five years later, those poor briefs have produced something more useful than a curious photo: one of the largest datasets on the biological functioning of Swiss soils.
The results of the citizen science project Beweisstück Unterhosecoordinated by the University of Zurich and Agroscope, the Swiss federal center for agricultural research, were published in the journal Plants, People, Planet and they show one thing above all: the way we use land matters a lot for what happens under our feet.
The ground ate my underwear, but at very different speeds
The experiment was less improvised than the wardrobe suggests. Each participant received two pairs of the same style of 100% organic cotton men’s briefs, except for elastic and synthetic stitching, along with 12 tea bags used as standardized plant material. Everything was buried following common instructions; participants recorded the location, type of soil and management methods via an app, then sent photographs, recovered underwear and soil samples to the researchers.
Around 1,400 people had applied within a few days. The researchers selected a thousand of them, trying to distribute the sites across the territory and ensuring that at least half of the participants were farmers. After checks and data cleaning, 780 sites remained in the scientific analysis. Not exactly four briefs buried behind the house to see the effect it has.
After one month the average decomposition of the underwear was 10.1%. After two months it had risen to 50.45%. The principle is simple: cotton is cellulose and bacteria, fungi and other soil organisms help to degrade it. The more material disappears, the greater the decomposition activity recorded under those conditions.
Private gardens devoured more cotton
The largest differences appeared between different land uses. The underpants degraded more in private gardens, which also had high amounts of organic carbon and nutrients. At the other extreme were mowed lawns, where activity detected through cotton was lowest. Cultivated land and permanent grassland occupied intermediate positions.
Among the variables analyzed, land use was the most important factor, followed by chemical characteristics. In particular, the main predictors were the availability of phosphorus and sodium, the type of fertilizer used and the quantity of silt. Decomposition also increased with organic carbon, nutrients and pH, while it tended to decrease with higher altitude, where temperatures are generally lower.
Here, however, a very tatty underwear does not automatically equate to a gold medal for the terrain. The same researchers point out that very high decomposition can be associated with an excess of nutrients. In private gardens, for example, available phosphorus levels were often well above agronomic thresholds. A slip that has almost disappeared can therefore suggest great biological activity and fertility, or warn that the fertilizer has been a little generous.
A panty does not make a soil diagnosis
There is also an important limitation. The statistical model used in the study was able to explain approximately 16.5% of the variability observed in decomposition after two months. In the subsoil, temperature, humidity, structure, microorganisms, management and many other factors come into play that a pair of briefs cannot neatly line up.
For this reason, the authors propose the “Underpants Index” above all as a simple indicator of decomposition activity and soil fertility, useful for obtaining a first impression and comparing different situations. Defining it alone as a comprehensive measure of “soil health” would be much more ambitious than the data shows.
However, the experiment has another rather obvious advantage: it makes visible something that we normally don’t see. Soil hosts a huge part of the earth’s biodiversity, stores carbon, holds water and nutrients, and supports food production. Yet, to the naked eye, it may simply look like brown earth. A new underwear that comes back two months later reduced to the elastic makes the concept decidedly less abstract.
The project also made it possible to collect data in around a thousand locations, a job that a small group of researchers would have had much more difficulty accomplishing alone. Approximately 240 participating citizens are among the co-authors of the publication, while all received information on the samples analyzed and indications for managing their land. Citizen science, this time, has reached the underwear drawer.
And if someone wanted to replicate the experiment in the garden, the meaning remains this: after a few weeks, very degraded cotton signals that there is a lot of activity down there. To really understand how that terrain is, analysis and context are needed. Underpants can start the conversation. It would be asking too much to expect them to also do the laboratory work.
