A Disappearing World Beneath Our Feet

As Midwestern farm fields take a long winter's nap, evidence is piling up that even when the temperature's above freezing, all that soil is basically in a bit of a stupor—so devoid of microbial life that it can't even produce a decent crop without getting a hit of chemical inputs.

The latest proof of this came in November when the journal Science published a University of Colorado paper quantifying what many farmers and conservationists have long suspected: when we converted tens of millions of acres of tallgrass prairie to annual row crops, it wasn't just the surface that was denuded of diversity. The incredible soil microbial diversity that once dominated the subsurface of native prairie areas has been "almost completely eradicated" by decades of monocultural row crop agriculture, according to the paper, which includes contributions from scientists based at some of the nation's most prestigious research institutions, including the Mount Sinai School of Medicine and the Argonne National Laboratory.

The paper bases its groundbreaking (pardon the pun) conclusions on how much of a certain bacterial group called Verrucomicrobia is present in the soil. Although little-studied, it turns out Verrucomicrobia dominate many prairie soils, making them a prime indicator of a rich ecological basement.

To take into account varying climate conditions, scientists sampled 31 native prairie sites—mostly cemeteries and nature preserves—from the Dakotas and Minnesota down through Iowa and as far south as Texas. They then compared the presence of Verrucomicrobia in the prairie samples to those taken from cultivated soils. It was a "before and after" contrast of the most striking variety—like walking through a factory after all the machinery, workers and energy inputs have been stripped out, leaving an empty, echoey building. "…the soils currently found throughout the region bear little resemblance to their pre-agricultural state," concluded the researchers.

That's bad news. As two South African scientists—Mary Scholes and Robert Scholes—writing in that same issue of Science warn, "An intact, self-restoring soil ecosystem is essential, especially in times of climate stress."

Image

And this isn't just a problem in America's grasslands. More than 46 percent of the world’s soil is suffering from noticeable productivity declines and partially destroyed biological functions, according to the International Soil Reference and Information Centre. As the University of Colorado paper shows, this is not just a Third World problem. "We have forgotten the lesson of the Dust Bowl: Even in advanced economies, human well-being depends on looking after the soil," write South Africa's Scholes and Scholes.

A dead soil is anything but self-restoring and resilient. We've been able to cover up soil's lack of life with plenty of chemical inputs, and we all know what the unintended consequences of that have been. More chemicals results in less microbial life, which means more chemicals are needed to retain yields—a vicious cycle if there ever was one. And whenever chemical inputs are increased, it's inevitable that some of those chemicals will find a way to become pollutants in the wider ecosystem—much like nitrogen fertilizer has here in Minnesota.

On the other hand, it's exciting to see what happens when soil is allowed to become more self-reliant. I recall sitting in the office of soil microbiologist Kristine Nichols as she showed me microscopic images of soil aggregates, groups of soil particles that bind to each other. As she explained it, healthy microorganisms can do something called “habitat engineering,” which has huge implications for allowing soil to cook up its own fertility and make efficient use of available moisture. It also has erosion reduction implications—soils with more organic matter feed themselves, and extra “food” goes into developing a waxy glue that holds aggregates together, creating a habitat where water can’t build up the kind of explosive pressure that sends particles off a field and into our water.

“They’ve actually engineered an environment that’s safe, that has food and has the ability to produce carbon to self-perpetuate,” Nichols explained to me. “The more of these aggregates there are, and the larger they are, the less susceptible to erosion the soil is. We’ve found management can impact this.”

She isn't speaking theoretically. The scientist's USDA office is just a few miles from Burleigh County, in south-central North Dakota. As we've described in this blog previously, farmers, conservationists and scientists are working together to build the kind of soil health that's resilient—biologically and economically.

Just as we will probably never see a return of a landscape dominated by tallgrass prairie, it's doubtful we will experience in our lifetimes Midwestern soils buzzing with the fully-functioning biology that was around pre-cultivation. But examples popping up in Burleigh County and elsewhere show there are practical ways to at least strike a balance between productive agriculture and healthy soil.

Southeast Minnesota farmer Duane Hager is striking such a balance through a combination of cover cropping, diverse crop rotations, grazing and use of livestock manure. Over the years, Hager has learned what works and what doesn't, and feels he'd gotten to the point where if he left some of his soils alone for a year, "they'd take care of themselves." After all, prairie soils pretty much ate their own cooking long before we arrived on the scene, the farmer points out. That kind of confidence comes with knowing what can be controlled, and what can't.

"No matter how you farm, you are disrupting nature's process," Hager told me recently. "But to realize that you are disrupting the process and work with it, that's important."

Brian DeVore is the editor of the Land Stewardship Letter.