University of Idaho buried cotton underwear in 34 Idaho fields for eight weeks; soil microbes broke down the cotton as a simple soil-health test

The University of Idaho has used the simple cotton underwear test in its Magic Valley Soil Health Project, where it has collected information about the condition of the soil in 34 fields for almost three years. In the test, cotton fabric is buried underground to give an indication of microbial activity in the soil. The soil contains billions of microbes such as bacteria and fungi that keep decomposing organic materials without making any noise. The more active the microbes are, the quicker they can decompose organic materials, including cotton. Therefore, the condition of a newly buried pair of briefs after two months can provide visual evidence of activity underground.

This way of thinking is part of an overall change in perceptions when it comes to soil. For a long time, soil was something that simply happened, something to till, plant into, and forget about. More gardeners and small-scale growers are paying attention to soil quality. Healthy soil can support healthier plants, help hold on to water, and reduce the need for some chemical inputs, among other things.

How a pair of underwear got to become a soil hero


The test itself couldn’t get any simpler. At the University of Idaho Extension, the Soil Your Undies test is used as a simple visual assessment. The team takes a brand new pair of cotton underwear, buries it, leaves it in the ground for eight weeks, then digs it up. Because cotton is a natural material, soil microorganisms feed on it; after eight weeks, the underwear may be badly decomposed, while the elastic waistband often remains mostly intact. The remaining material can then be weighed to calculate the loss rate.

Based on the published research summary of the project, the simple visual assessment was supplemented by a more complex technical approach involving tests such as phospholipid fatty acid analysis and the Haney test, which focus on nutrient cycling and microbial biomass. The early findings from the fields being tested, as stated in the research, indicated that the highest levels of biological activity were observed in fields with no-till perennial management practices. This finding is relevant to gardening and farming because reduced soil disturbance can help support biological activity and soil structure, which are associated with nutrient cycling and water retention.

How it is applicable in home gardens

You do not require thirty-four fields or a grant for some of these soil-health practices to apply in a garden. As long as you cultivate vegetables, have a flower bed, or even a small lawn to take care of, some soil-health concepts can also apply in home gardens. According to extension guidance, adding organic matter and avoiding unnecessary disturbance of the soil can help improve soil structure, biological activity, and plant growth. Composting kitchen leftovers, allowing fallen leaves to decompose naturally instead of disposing of them in bags, and tilling garden beds less frequently can support the soil ecosystem.

Good soil does not happen overnight, and the Magic Valley project has collected information over an extended period because soil health can respond gradually to consistent management practices. A single season of composting may not produce major changes in a garden bed, but consistent additions of organic matter and low-disturbance care can gradually improve soil over time.

For anyone curious about trying a similar demonstration at home, a small piece of plain cotton fabric could be buried in a few spots around a yard or garden and checked after several weeks. The amount of fabric breakdown may offer a rough visual indication of microbial activity, but it should not replace professional soil testing. Patches with more biologically active soil may show faster cotton breakdown than areas that are compacted or heavily disturbed.

The underwear test offers a memorable way to talk about soil health and make microbial activity visible. Soil health is never a very exciting topic for discussion over dinner, but a tale of some missing underwear in the soil can draw attention to what is happening underneath gardens, yards, and farms. The more biologically active the soil, the healthier it may be, whether that is measured scientifically or suggested by a cotton test.