Results of the citizen science project on assessing soil activity

As part of the "Proof by Underpants" research project launched in 2021 by researchers from the University of Zurich and the Swiss federal agricultural research station Agroscope, about 1,000 volunteers buried more than 2,000 pairs of identical cotton underwear and 12,000 tea bags in their plots. The materials were retrieved after one month and two months to assess the degree of their decomposition by soil microorganisms.

The study, published on August 26, 2026, in the journal Plants, People, Planet, revealed differences in the rate of fabric breakdown depending on the type of land use. Over two months, about 58% of the fabric decomposed in home gardens, approximately 51% in arable fields, about 47% in permanent grasslands, and about 40% in lawns. The scientists attribute the poor performance of lawns to frequent mowing, low plant diversity, and the use of herbicides.

Comparing the degree of fabric destruction (the underpants index) with the standard tea bag index made it possible to assess soil activity. At the same time, in some home gardens, the level of available phosphorus averaged about 13.7 milligrams per kilogram, which exceeds the optimal Swiss range and is four times higher than the figures in arable fields. According to the authors, rapid decomposition is not always desirable and may indicate an excess of nutrients and over-fertilization of soils.

Members of the team behind the project were awarded the 2026 Ig Nobel Prize in soil science. As practical measures to support soil life, experts recommend keeping the soil covered year-round, adding compost, diversifying crop rotations, and limiting the use of mineral fertilizers and pesticides.