Soil health assessment using buried cotton underpants with the help of 1000 citizen scientists

Societal Impact Statement Soil is a vital resource for life on Earth. Although many soils are degraded, societal awareness of soil‐related issues is limited. To highlight soil as a key resource and fascinating study system, we initiated a citizen science project together with 1000 participants investigating soil health across Switzerland using buried cotton underpants. The degree of underpants decomposition was interpreted as a measure for soil biological activity and soil health. This work demonstrates that underwear decomposition varied widely across land‐use types and that buried underwear is a simple and easily interpretable tool to gain a first impression of soil health. Summary Soil is a vital resource for plant growth. It hosts a major part of global species diversity and is key for ecosystem functioning and it forms the basis of human civilization. Yet soils are rapidly degrading, threatening food production, biodiversity, and Earth system functioning. This threat is largely unrecognized in broader society, hindering effective steps towards soil protection. In a citizen science approach, involving 1000 citizen scientists burying more than 2000 cotton underpants and 12,000 teabags across 1000 locations, we aimed to assess soil biological activity and soil health in Switzerland. Decomposition of underpants and tea bags was considered as proxies for soil biological activity and soil health. Underwear decomposition differed greatly across land‐use types, indicating significant variation in soil biological activity among sites. Land use was the most important predictor of decomposition processes, followed by soil chemical parameters. Private gardens, the land‐use type with the highest levels of soil organic carbon and nutrients, exhibited the greatest biological activity, whereas lawns showed the lowest, with croplands and grasslands falling in between. Overall, 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. We propose the “Underpants Index” as an accessible, engaging method to assess soil decomposition processes and soil fertility and raise public awareness for soil as a vital, yet threatened resource.