A pinch of compost from Alter Eco Farms contains a world invisible to the naked eye.
Cofounder Krisi Olivero reveals it by mixing a small amount of the dark, crumbly material with water, placing a single drop on a glass slide and slipping it beneath a microscope. Magnified hundreds of times, what looked like little more than dirt begins to teem with life.
Olivero points to tiny dots scattered across a screen and identifies them as bacteria. A long, branching strand is a fungal hypha. There are protozoa, amoebas and nematodes, including one that wriggles through the sample while feeding on bacteria clinging to a piece of decomposing organic matter.
Somewhere among them might even be a tardigrade, one of Olivero’s favorite microscopic creatures.
And this is just one drop.
At 400-times magnification, Olivero estimates there are about 2,800 individual fields of view in that drop of water – each offering another tiny patch to explore.
“There’s another world in that drop of water,” I tell her as we peer at the monitor.
“And it’s a world most of us are unaware of,” she replies.
For Olivero, that hidden world is a living system that helps make the soil beneath our feet work.
Bacteria and fungi extract nutrients from mineral particles in soil. Other microscopic organisms consume them, helping convert those nutrients into forms plants can use. Together, they form a complex food web that Olivero says healthy soil and the plants growing in it depend on.
Yet much of the soil people farm, garden and walk across every day has lost some of that biological diversity, Olivero says. Her work at Alter Eco Farms, near Chattanooga, centers on putting it back.
The farm produces what Olivero calls “living compost,” using a carefully managed thermophilic, or hot-composting, process designed not simply to turn organic material into compost but to cultivate a diverse community of microorganisms.
The finished product can then serve much like a sourdough starter, inoculating soil with microscopic life. Alter Eco also produces a liquid compost extract that allows those organisms to be applied over larger areas.
It’s work Olivero could hardly have imagined doing several years ago. Soil biology is a second career for the former advertising professional, who says she entered the field knowing so little that an introductory webinar left her simultaneously bewildered and convinced she’d stumbled onto something important.
“I had zero clue what they were talking about,” she remembers, “but it appeared to be wildly important.”
Since then, Olivero has spent years studying the biology beneath our feet – and wondering why something so fundamental remains largely invisible not only to our eyes but also to our understanding.
“Most of us think, ‘Oh yeah, the ground. That’s the end. The world ends at our feet,’” she says. “That couldn’t be further from the truth.”
Cultivating life
Making that living compost requires Olivero to walk a narrow line between heat and life.
As a compost pile cooks, she keeps a close eye on its temperature. The goal is to get the pile hot enough to kill pathogens and seeds while keeping it below the point at which the microorganisms she’s trying to cultivate begin to die.
“The microbes start to die if we go above 170 or 175, which is not what we’re trying to do,” she says.
At about 180 degrees, she adds, the compost could spontaneously combust.
“We really don’t want to hit that,” she says. “We don’t want to play that game.”
What goes into a pile varies. Alter Eco uses material from the farm, including grass, weeds and whatever else happens to be growing in its pastures. Because the pile becomes hot enough to kill the seeds, even weeds can be put to productive use.
“We actually bring weeds to a higher calling,” Olivero says.
The first piles were inoculated with microorganisms gathered from old-growth forest soil. Olivero says a quarter cup was enough to inoculate a 300-gallon pile.
Those microorganisms are part of the biological system Olivero hopes to restore in depleted soil.
“If you go into an old-growth forest, no one’s out there fertilizing it, right?” she says. “It’s taking care of itself.
“A lot of people say, ‘Oh, I have to add fertilizer to my garden.’ But why do you have to fertilize your garden when nobody has to fertilize the forest? A big part of the answer is soil microorganisms.”
For Olivero, the lesson is that a healthy microbial community helps continually cycle nutrients in the soil into forms plants can use.
“You’ll see bags of beneficial bacteria in stores now that say, ‘For your garden,’” she says. “But if you don’t have beneficial protozoa as well, you’re missing a piece. The bacteria won’t help.”
Olivero says human activity has damaged many of those communities, creating a cycle in which soils become increasingly dependent on added nutrients as the organisms that once helped make nutrients available to plants disappear.
“Poor little tardigrades,” I say.
“Poor little tardigrades,” she replies.
Learning to look
Olivero’s own introduction to that loss came when she began putting soil beneath the microscope.
The first microscope she ever used was the one she bought for her soil biology training. She’d never used one in high school, and when the instrument arrived in pieces, the directions seemed to assume she knew considerably more than she did.
“I was like, ‘Which part goes where?’ I had no idea,” she says.
Even finding focus was a challenge.
“I felt so naive, like, ‘Oh my God, what am I doing? I have no idea.’ One more slice of humble pie.”
Olivero also accidentally ordered a set of pre-mounted slides when she thought she was buying blank ones. She decided they’d at least give her something to practice focusing on.
“You never know what they’re going to be,” she says. “I threw one under there and thought, ‘Wow, this is so interesting. What am I looking at?’
“And it was a Pap smear.”
She still keeps prepared slides nearby for troubleshooting. A few months ago, she fell down a flight of stairs while carrying her microscope in its case and feared she’d damaged it. Having a known sample to focus on suddenly proved reassuring.
“I have one that’s a bee, and I always try to focus on its knees – my little bee’s knees.”
Learning to operate the microscope, however, turned out not to be the reason she initially struggled to find the soil life she’d studied.
When Olivero began taking soil from her yard and examining it, she expected to encounter the creatures she’d learned about. Instead, she saw little.
“I was like, ‘Well, where are they? I must be doing something wrong because I can’t find them.’
“But that wasn’t the case. There was just nothing living in most of the soil I was examining.”
She kept trying.
“I’d dig some soil out of the yard and think, ‘Let’s throw it under the microscope and see what I find.’ And I didn’t find much.”
Then she found her first nematode.
“It was so exciting,” she says. “I told the whole house.”
Nematodes look like tiny snakes, she explains, and their constant movement makes them easy to spot. One appears on the monitor as Olivero examines the compost sample.
“There’s a nematode,” I blurt out.
“See?” she replies. “You knew it when you saw it.”
The nematode is feeding on bacteria clinging to a piece of decomposing organic material. As it squirms across the screen, I can see material moving through its translucent body.
“That’s what plants can use?” I ask.
“Yup,” she says. “Now you should have no trouble with explaining this to others. It’s weird that this isn’t common knowledge because the basics are so accessible.”
The microscope is an important part of Olivero’s work. She uses it to monitor the compost, checking piles every couple of weeks to make sure the organisms she expects to find are there.
She also analyzes soil for clients. Alter Eco works with farms and home gardeners, testing soil to see what’s happening beneath the surface and determine what it needs. From there, clients can have Alter Eco apply compost or extract, or purchase the products and do the work themselves.
From microscope to field
Moving those organisms from a compost pile into acres of soil presents another challenge. Solid compost is heavy and cumbersome, so Alter Eco turns it into a liquid extract using a piece of equipment Olivero calls a “compost car wash.”
Water applied at the proper pressure washes the microorganisms from the compost, creating a liquid that can be sprayed or otherwise delivered to soil. The approach allows Alter Eco to work beyond backyard gardens.
Olivero says the farm has applied extracts to pasture and worked with an orchard where she injected the material directly into the root zones of trees.
“That must have taken some time,” I say.
“It did,” she says. “Soil work is not quick work.”
Nor does Olivero believe it should be the exclusive domain of farmers, scientists or people with large tracts of land.
“Soil science can feel really niche, like, ‘I’m an average person. What does soil science have to do with me?’” she says. “But soil science is everybody’s business.”
A person with a small backyard garden can participate, she says, and she wants more people to learn how. For all the complexity she sees through her microscope, Olivero’s final message is strikingly uncomplicated.
“I want everybody to feel like they can be part of this really cool science,” she says. “It’s not just for nerds. It’s not just for rich people.
“It’s for anybody who eats.
“Soil science is for anybody who eats.”