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The Cotton Test aka Soil Your Undies

by Neil Sass, Natural Resources Conservation Service Soil Scientist aka Soil Nerd

A healthy, functioning soil provides many things from beans and clean water for your morning coffee to flood mitigation and carbon storage for communities worldwide.

A healthy, functioning soil will also decompose residues and recycle nutrients. So when I observed that my potted plant residues weren’t breaking down I decided to try a little experiment with the Cotton Test to try and figure out why.

The Cotton Test aka Soil Your Undies is a test for soil biological activity. It's kind of like fishing where you provide an easy meal and see if anything nearby wants a quick snack. The Cotton Test does this by providing a tasty carbon food source for soil organisms like bacteria, fungi, earthworms, millipedes, sowbugs, and arthropods. I had conducted this experiment in the past on several different soil management systems at a larger farming scale, my results looked like this:

For Soil Your Undies version 2.0 I decided to set my plot treatments up in the Fayette County Conservation Lasagna Garden thinking that there should be some good biological activity going on there due to the composting and layering techniques that they were doing.

My hypothesis was that soil critters in the healthy garden soil would eat all of the cotton undies. The ones in the potting soil would only be slightly eaten.

So I set my plots up like this to try and answer the question of could soil critters eat the snack, and if so, how quickly will they find it:

The 100% cotton (except for the elastic bands) undie food source was buried on May 24, 2020. It was buried 2 inches deep with the waistband sticking out as shown above.

The soil organisms then snacked for approx. 6 weeks.

The undies were dug up on July 5, 2020, and were dried and soil particles lightly brushed off.

They were then weighed on a digital scale to determine the change in weight of cotton material.

What does this mean?

All pairs of undies that were buried in the Sedlmayr Lasagna Garden were almost completely decomposed (minus the elastic parts). The percent decomposed of these 3 was near 50%. These cotton snacks were deliciously enjoyed by the soil biological organisms, even the one where the potting soil had a barrier between it and the healthy garden soil. This garden soil efficiently decomposes and cycles nutrients while providing nutritious food. It is a healthy functioning soil

The same cotton undies in the same potting soil but left inside only decomposed 3.4% in the same amount of time. Something is missing here….. there are no organisms present to eat the cotton snack and this soil is not fully functioning.

This tells me that the bagged potting soil itself does not contain the soil organisms that are responsible for breaking down the cotton organic material. It is a medium, but not an inoculum.

The potting soil that was placed in the ground or even in a pot buried in the ground did acquire the soil organisms relatively quickly just by being outside.

Soil scientist recommendation: Soil health is affected by management, not just parent material. Get outside to be healthy.

Special thanks to Fayette County Conservation and the Sedlmayrs for use of their Lasagna Garden, and Reagan Sass for her help with the plots.

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