Scientists estimate that more than half of global biodiversity exists below the surface. But soil biodiversity is declining around the world, threatening agriculture, food security and the ability of ecosystems to function properly. To investigate this hidden world, researchers from the University of Zurich (UZH) and Agroscope, the Swiss federal center of excellence for agricultural research, launched the citizen science project Proof by Underpants (Beweisstück Unterhose) in 2021.
The project was designed both to raise awareness of soil ecosystems and to generate scientific data. Following the same standardized method, 1,000 volunteers buried more than 2,000 pairs of cotton underwear and 12,000 tea bags at roughly 1,000 sites across Switzerland. After two months, participants dug them up, photographed them, and sent the material to the laboratory along with soil samples for further study.
Decomposing Underwear Reveals Soil Activity The findings, published in Plants, People, Planet, produced a broad map of biological activity in Swiss soils. Researchers found that the cotton underwear broke down at very different speeds depending on where it was buried. That decomposition rate served as a simple indicator of how much biological activity was taking place underground.
When soil organisms were more active, they broke down the cotton more quickly. Private gardens showed the fastest decomposition. Researchers also found that these soils contained the highest amounts of organic matter, creating favorable conditions for earthworms, fungi, bacteria, and other organisms that live in soil.
Lawns showed the lowest level of soil organism activity. Agricultural fields and meadows ranked between gardens and lawns. "Our results show that how soil is managed can significantly affect both soil life and soil quality," says co-study leader Marcel van der Heijden, UZH professor of agroecology.
"Healthy, biologically active soil is crucial for fertility, nutrient cycling and many other ecosystem services." The researchers point to several practices that can encourage soil life. These include keeping soil permanently covered, applying compost, using more diverse crop rotations and reducing the use of mineral fertilizers and pesticides. Among the factors studied, land use had the strongest influence on how quickly the underwear decomposed.
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