Undies, jocks, drawers... There are plenty of names for underwear around the world.

Now, a group of farmers in Tennessee, in the United States, has found a new use for them: to test their soil.

The Coffee County Soil Conservation District is an environmental conservation organisation in Manchester, south of Nashville, where the main industries are corn, soybeans, and cattle grazing.

On July 3, the organisation buried several pairs of cotton underwear across the region in different soils that had been managed in varying ways.

"This is just a simple test where you can compare some different management systems," said district conservationist Adam Daugherty.

"The theory is, the more active the microbes in your soil are, the quicker the underwear cotton fibres will be consumed by the biology."

Mr Daugherty said the idea was to show farmers how important their off-season management was in the success of future crops.

"Traditionally, fields sit idle [between crops] with harvested residue from the combines on them," he said.

"We've filled a niche in this time with diverse cover crop systems, keeping a live plant growing and absorbing sunlight all year long.

"What we're doing this for is trying to biologically repriming, rejuvenating our soils."

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While the idea of off-season ground cover is not new, using cotton underwear to prove the system is working is certainly novel.

"Most times, when you think about 'soiling your drawers', it's not what we're doing by burying them and measuring biological activity," Mr Daugherty said.

"It's got a bit of a different outcome but that's the comedy behind it."

The knickers were unearthed a month later, on August 3.

Mr Daugherty said results highlighted that microbes needed carbon to survive — whether it be from plant matter or underwear — and if an idle field was planted with crop cover, the soil biology would stay healthy.

"That's why it's so important that we keep a living plant growing," he said.

"Because we will consume a lot of the readily-available organic matter that we have in the soil if we do not keep priming it and keeping that living plant growing."