Scientists Buried 2,000 Pairs of Underpants Across Switzerland to Test Soil Health

They wanted our attention, and they have certainly got it.

Across Switzerland, scientists buried more than 2,000 pairs of underwear in gardens, meadows, fields and lawns.

Unfortunately, it was not the beginning of an ambitious national game of hide-and-seek.

Instead, it was a rather literal attempt to expose our dirty laundry.

When the researchers unearthed the cotton underpants two months later, some pairs were reduced to little more than skeletal seams, whereas others had only developed one or two holes.

The results from the project, named "Proof by Underpants", have been published in the journal Plants, People, Planet.

Its purpose was to reveal that some soils may be surviving by little more than a G-string.

"Overall," the study authors write, "this project demonstrates that underpants can serve as a simple and easy-to-interpret tool, providing informative insights into the state of soils.

"Moreover, they are perfectly suited to raise attention in society for soil."

To draw wider attention to soil as a resource under threat, the team, led by researchers at the University of Zurich, has suggested an "Underpants Index".

According to the scientists, underwear with few or no holes can be a striking indication that nutrients are lacking. These nutrients support abundant biological activity, so their absence is a serious concern.

"This was one of the most intense but also most rewarding experiences of my scientific career so far."

• agroecologist Franz Bender

Why soil health matters

The planet's topsoil works quietly beneath our feet to help produce 95 percent of our food.

It is also home to 59 percent of global diversity and represents Earth's second-largest carbon reservoir, behind only the oceans.

Without productive, healthy soils, the very basis of human society would fall apart.

And here is the troubling part:

"Soils are rapidly degrading, threatening food production, biodiversity, and Earth system functioning," write the researchers responsible for "Proof by Underpants".

"This threat is largely unrecognized in broader society, hindering effective steps towards soil protection."

There is, however, a remedy: we need to alter the way land is used.

The Underpants Index and land use

In the underwear research, land use was the strongest single factor predicting how effectively the underwear broke down.

Swiss lawns, croplands and grasslands showed the lowest evidence of biological activity.

Indeed, grass monocultures surrounding many homes and buildings contained the least fertile soils of all.

By comparison, private gardens appeared to support the most active decomposers, including worms, fungi, bacteria and other organisms that live in soil.

They also had the greatest amounts of organic carbon and nutrients. This may be because their owners often carefully plant, fertilise and aerate their gardens.

After two months in a private garden, roughly 58 percent of the cotton had decomposed.

Lawns, on the other hand, recorded the lowest rate of decomposition, at an average of about 40 percent.

"Our results show that how soil is managed can significantly affect both soil life and soil quality," says Marcel van der Heijden, an agroecologist at UZH and co-leader of the study.

"Healthy, biologically active soil is crucial for fertility, nutrient cycling and many other ecosystem services."

Tea bags and cotton strips have previously been used to assess soil health, but the Swiss researchers consider underwear more "playful" and an "excellent outreach tool".

The underwear trials took place five years ago with help from 1,000 volunteers. Together, they buried cotton underpants and 12,000 tea bags in a range of landscapes around the country.

Two months afterwards, the volunteers recovered the materials and sent them to a laboratory for additional analysis.

The tea bags and underpants delivered comparable findings: both decomposed most rapidly in private gardens.

These results match those of another recent citizen-science project in Hungary, where underpants also broke down faster in managed kitchen gardens.

Fertility is not always healthier soil

Yet, while these private plots displayed stronger indications of nutrients and biological activity, higher soil fertility is not invariably beneficial.

Concentrations of phosphorus, nitrogen and potassium were greater in Switzerland's private gardens, pointing to fertiliser use. However, even a good thing can damage soil health when there is too much of it.

Phosphorus levels in private gardens frequently exceeded the thresholds used for soil management and crop production, which could endanger nearby waterways and local biodiversity.

"Maximum decomposition is not desirable in every ecosystem," explains Franz Bender, co-project leader and UZH agroecologist.

"In near-natural habitats such as forests, very high nutrient levels can indicate disruptions to the natural balance of nutrients. In gardens, too, rapid decomposition of the underwear may point to an oversupply of nutrients."

The Underpants Index could therefore show which soils are the most 'fertile', rather than necessarily identifying those that are healthiest.

Establishing that would need further on-the-ground analysis.

Nevertheless, Switzerland's citizen-science effort has already created one of the nation's most comprehensive datasets on soil life.

"This was one of the most intense but also most rewarding experiences of my scientific career so far," Bender said in a post.

Its results can guide researchers towards soils that might require more support and attention.

Perhaps dirty underpants will one day be excavated in other regions of the world as well.

The study is published in Plants, People, Planet.

This article was fact-checked by Clare Watson and edited by Clare Watson. Although we take pride in our process, we are only human. If you notice an error, please let us know.