Soil microbes require carbon to grow. And they’re not picky where that carbon comes from.
To demonstrate microbial activity as it relates to soil health, Manitoba Agriculture soil management specialist Marla Riekman and some colleagues buried what she calls “an indicator material” in various locations this spring. Their material of choice: cotton, specifically the soft, white fiber used to make men’s underwear.
“Basically, the microbes in the soil can’t tell the difference between the non-organic Walmart-purchased carbon source versus the crop residue carbon source in the soil,” she explains, in the video below.
As part of the annual Crop Diagnostic School in Carman, she dug up two of the soiled stashes: one from a forage stand and the other from her colleague John Heard’s adjacent corn plot.
Knowing that forages are beneficial for microbial activity, it might be surprising that the pair buried in the forage stand was much more recognizable, with the corn tighty-whities looking more like something R-rated for cavemen — an elastic waistband with a few threads.
Jokes and inappropriate innuendo aside, the quicker decomposition in the corn occurred because the underwear was buried near a nitrogen fertilizer band, where the bugs had easy access to N, notes Riekman.
“In order to break down carbon, the microbes need nitrogen as an energy source, so they really went to town on this pair of underwear (from the corn) and broke them down.”
Access to oxygen is also essential for microbial activity. The corn plot was oxygenated via heavy tillage in spring, and located slightly higher on the slope in less saturated soil, fostering decomposition.
Riekman says the underwear test shows that high microbial activity isn’t necessarily an indicator of “healthy soil.”
“John is quite happy with how the underwear looks in his corn plots because of the fact he’s looking for a high turnover of residue. He’s happy the bugs are very active and breaking down residue,” she explains.
From an environmental standpoint, she prefers the slower microbial activity in the forage.
“This makes me happy to see the forage is actually a slower decomp. A lot more of the carbon is going down into the roots, becoming part of the soil and being sequestered, as opposed to the carbon with the underwear in the corn. A lot of it is just going up into the atmosphere.”
Ragged or intact, it turns out tighty-whities can tell you how active carbon-loving microbes are, but whether the cotton’s fate is indicative of soil health or productivity still depends on how you define and measure it.
Related: Heavy Rains, Nutrient Losses and the Case for “Variable Source” Nitrogen
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