A pair of cotton underwear may seem an unlikely tool for measuring soil health, but scientists and farmers are using the unusual experiment to understand what lies beneath the ground. From a Canadian farmer who discovered changes in his soil over a decade to a Swiss research project involving more than 1,000 volunteers, the “Soil Your Undies” initiative is drawing attention to the importance of healthy, biologically active soil.Norm Lamothe and his family operate a 500-acre farm outside Peterborough, Ontario, in Canada. In 2015, Lamothe learned about the “Soil Your Undies” campaign launched by the Soil Conservation Council of Canada and decided to try the experiment himself.The idea was simple: bury a pair of cotton underpants in the soil, leave them underground for a few months and then dig them up to see how much they had decomposed.Agricultural experts explained that the breakdown of the cotton could offer a rough indication of microbial activity. Healthy soil contains microorganisms that feed on organic matter, including cotton fibres. The more the underwear decomposes, the greater the evidence of biological activity in the soil.However, Lamothe was disappointed by what he found when he first retrieved his underwear. His white Hanes underpants were still largely intact.“That’s really what started my journey down the soil health path,” Lamothe told The Narwhal. “Much to our chagrin, they were completely intact.”The result prompted him to look more closely at the condition of his farm’s soil and explore practices that could improve its biological health.
Crop rotation and sheep help improve soil conditions
Following the initial experiment, Lamothe joined farmer peer groups, including the Ontario Soil Network and Farmers for Climate Solutions, to learn more about soil conservation.He began diversifying his crop rotation, growing corn, soybeans, winter wheat and oats. This was twice the variety he had previously cultivated, helping reduce reliance on a narrower selection of crops.He also introduced hay to help prevent erosion and keep the soil anchored. In 2022, he brought sheep onto the farm to graze the hay. Their manure helped return nutrients to the ground.These changes were part of a broader effort to improve the soil’s condition through more diverse agricultural practices and natural nutrient cycling.A decade after his first attempt, Lamothe repeated the underwear experiment. This time, the results were different: the cotton had decomposed considerably more.“Whether the change came from our practices or differing weather conditions is up for debate, but certainly we saw we had microbial activity,” Lamothe told The Narwhal.The retrieved underwear now hangs framed in his office, serving as an unusual conversation starter for visitors curious about why a farmer would display a pair of old underpants.
Why scientists say healthy soil needs billions of microbes
The idea behind the experiment is rooted in the role microorganisms play in maintaining healthy soil. Bacteria, fungi and other soil organisms break down organic matter, recycle nutrients and support the processes that help plants grow.The United States Department of Agriculture’s Natural Resources Conservation Service has also promoted the experiment, providing guidance for farmers and gardeners interested in examining soil health.“Healthy soil contains billions of microbes that consume the cotton,” the agency explains in its guidance. It also notes that one teaspoon of healthy soil contains more microbes than there are people on the planet.Beyond decomposing organic matter, these organisms help soil resist erosion, cycle nutrients and store water. These functions are important for agriculture and for the wider environment.The underwear test is not a complete scientific assessment of soil quality, however. Decomposition can also be influenced by weather, soil moisture, temperature, the type of soil and the length of time the cotton remains buried. It is best understood as a simple indicator of biological activity rather than a definitive measure of overall soil health.
Swiss researchers bury more than 2,000 pairs of underwear
The experiment has also become a citizen science project. In 2021, researchers from Agroscope, Switzerland’s federal centre of excellence for agricultural research, collaborated with scientists from the University of Zurich on a project called “Proof by Underpants”.The initiative recruited more than 1,000 volunteers across Switzerland to bury cotton underwear and tea bags at locations throughout the country.Participants buried more than 2,000 pairs of underpants and 12,000 tea bags at nearly 1,000 sites. After two months, they dug up the materials and sent the underwear, along with accompanying soil samples, to the University of Zurich laboratory for analysis.The large-scale experiment allowed researchers to compare decomposition across different environments, offering insight into how soil management and land use affect biological activity.
Gardens have the fastest soil decomposition rates
The study’s findings, published on August 26, revealed differences in decomposition rates across land types. Private gardens showed the fastest decomposition, while lawns recorded the slowest. Agricultural fields and meadows fell between the two.The results highlighted how the condition and management of soil can influence the organisms responsible for breaking down organic matter.“Our results show that how soil is managed can significantly affect both soil life and soil quality,” said study co-leader Marcel van der Heijden, a professor of agroecology at the University of Zurich.“Healthy, biologically active soil is crucial for fertility, nutrient cycling, and many other ecosystem services,” he added.The project also benefited participants, who received individual feedback based on their samples to help them make more sustainable decisions about managing their gardens and other land.
‘Underpants Index’ could make soil science more accessible
The Swiss researchers said the experiment demonstrated how an ordinary cotton garment could help make a complex scientific subject easier for the public to understand.“Overall, this project demonstrates that underpants can serve as a simple and easy-to-interpret tool, providing informative insights into the state of soils,” the researchers wrote in their study, published in the scientific journal Plants, People, Planet.They proposed an “Underpants Index” as an accessible way to assess soil decomposition processes, offer clues about soil fertility and raise awareness about soil as a vital but threatened resource.Although burying underwear cannot replace laboratory testing or a comprehensive soil assessment, the experiment offers farmers, gardeners and researchers an engaging way to observe biological activity.