Underwear Measures Soil Microbial Activity

The Volsen family buried underwear in a variety of soil conditions to see determine microbial activity. ( Amanda Volsen )

As Amanda Volsen and her husband buried four pairs of new cotton underwear they were bombarded with questions from their four young children. The biggest, and the one you might be wondering: Why are you burying underwear?

In recent years, Volsen and her husband have gained a new appreciation for soil health on their southern Minnesota corn, soybean and small grain farm. The ‘soiled undies’ test gave them the opportunity to see what fields contained the greatest amount of microbial activity, and what fields still have improvements to make.

“My husband has been farming since he could walk with his grandpa and his dad and in the last couple years he’s been looking more into cover crops and conservation tillage practices,” Volsen says. “We had a few fields of no-till already because they were highly erodible but we’re really digging into the addition of cover crops.”

The family has been experimenting with cover crops for the past three years now. This experiment gave them proof that their efforts are creating healthier environments for microbes.

“In the four pairs of underwear buried, the one with just the waistband left was five-year no-till and three-year cover crop,” Volsen says. “The one pretty much intact was just corn and bean rotation along with conventional tillage.”


Farmers who perform the soil your undies test are essentially using the garment as a surrogate for a corn stalk for a more uniform comparison of soil health. USDA Natural Resources Conservation Services and others have in the past encouraged the practice so farmers get a real feel for what soil is doing on their fields.

“If I were doing this I would look at the characteristics of the fields I wanted to improve and the current management practices,” says Michael Lehman, research microbiologist is USDA Agricultural Research Laboratory. Breakdown and decomposition boils down to whether the microbes have food and the structure of the soil.

“They need food, importantly they need root exudates,” Lehman says. When plants are alive they produce energy through photosynthesis, but about 20% of that is lost in the soil through the roots. Live roots in the soil longer give those exudates to the microbes to stimulate more activity, which leads to faster decomposition and assists in healthy soils, he adds.

This extra energy is likely why the Volsen family saw the most underwear decomposition in the field with cover crop and no-till. In addition, research shows that no-till and minimum till also supports better soil structure than conventionally tilled fields.


“If you have a soil structure that permits air and water to flow through you have increased microbial activity,” Lehman says. Fields with poor soil structure, often promoted by aggressive tillage and fallow periods don’t provide the oxygen and water microbes need on a continual basis.

“However, right after you till up soil it creates a burst in microbial activity but it won’t be sustained and as the soil settles the structure isn’t that great and restricts air and water flow, causing low activity,” Lehman says. “It’s also more susceptible to ponding [which can reduce microbial activity].”

He says the better option is year-long moderate activity through improving soil structure and providing food in the form of root exudates. If you do the underwear test and 60 days later find it still intact, Lehman says to take steps to add a new crop to your rotation, reduce tillage, retain residues and try to keep something growing in the field as long as possible.

On the Volsen farm, the test was a reminder and evidence that their efforts to help soil are working.

“We work with multiple generations on the farm, so it was nice to have proof in the underwear of what we’re seeing in crops,” Volsen says. “Cover crops and conservation practices aren’t a magic solution, it requires proper management and you can’t just try it once, there’s a learning curve to make it work for you operation. But it’s worth it.”