When Bill Robertson, a soil scientist at the University of Arkansas, wants to check whether a field is healthy, he doesn’t reach for some high-tech gadget. He grabs a pair of men’s 100% cotton underwear.
“I call it the ‘Soil Your Undies’ test,” he said, describing how he buries the underwear 2 to 4 inches deep, leaving the waistband showing so he can find them and dig them up five weeks later.
“Soil creatures — bacteria, fungi and nematodes — eat cellulose, and those briefs are basically cellulose,” Robertson explained. “If that soil is alive then, after five weeks, (the underwear) should fall apart like a wet newspaper.” If, on the other hand, the soil isn’t thriving, then what is left is a dirty, but intact, set of briefs.
Until recently, Robertson said, most agricultural experts thought of soil as nothing more than a matrix to hold plants and minerals. But the same technologies that have allowed us to better understand the bacteria and fungi that make up our microbiome have led to breakthroughs in soil science.
What they are showing is that those underwear-munching microbes play key roles in preventing soil erosion, conserving water and breaking down environmental pollutants. They also capture and store atmospheric carbon — which might help fight climate change.
If this were all soil microbes did, they would clearly be central to our well-being and survival on this planet. But emerging research suggests that the soil microbiome might have an even more direct effect on our health by communicating directly with our own cells and by boosting the nutrient content of our food.
“For a long time, (scientists) have been obsessed with the idea is that there are things in the soil that are trying to kill us,” said Rob Knight, a microbiologist at University of California at San Diego who studies communities of microbes, including those that typically live in soil and those that inhabit our bodies. He mentioned several disease-causing soil dwellers, including tetanus, that are often held up as proof that soil is a dangerous place.
But recently, Knight said, scientists have begun to abandon their “war metaphor.” Instead, they are exploring ways that microbes in the soil might protect us.
He gave the example of Mycobacterium vaccae, a benign soil-dwelling bacteria that was first identified on the shores of Lake Kyoga in Uganda in the 1970s. Researchers at the University of Colorado Boulder have observed that heat-killed M. vaccae has immune-modulating and mood altering properties when it is injected into experimental mice. While the studies have yet to be replicated in humans, the thinking is that M. vaccae, along with a host of other microbes that live in soil and the natural environment, coevolved with us and have the power to communicate with our own cells.
Donata Vercelli, professor of cellular and molecular medicine at the University of Arizona, studies how these ancient microbes affect our health.
Her interest was sparked about a decade ago when she learned that farm children in Germany had lower rates of allergy and asthma than their counterparts raised in urban areas. She joined a multinational research team to understand what was behind this phenomenon.
She explained that the constellation of organisms found in soil and on farm animals programs how a child responds to allergens throughout a lifetime. This programming probably starts in utero and continues to shape the immune system during the first few years of life.
Soil microbes help regulate our emotions and immune response. They also play a key role in determining the nutrient content of our food.
Cornell plant scientist Jenny Kao-Kniffin studies the underground interactions that take place between soil microbes and the roots of plants, a zone she refers to as the phytobiome.
“This could be the next frontier in nutrition science,” said Kao-Kniffin, explaining how plants secrete compounds to feed nearby microbes and, in exchange, the microbes enable plants to capture essential nutrients (such as nitrogen) and manufacture a series of chemicals called phytonutrients or antioxidants.
These chemicals protect plants from pests and other stressors; they also give fruits and vegetables their color, smell and distinctive flavor. Research shows that these same chemicals directly benefit us by stimulating our immune system, regulating our hormones and slowing the growth of human cancer cells.
Kao-Kniffin’s most recent finding is that soil with a diverse microbial community promotes plant growth while soil with more homogeneous microbial makeup suppresses growth.
Throughout most of his career, Robert Beelman has focused his research on quantifying the antioxidant content of plants and describing how these nutrients affect our own cells. But recently, Beelman, an emeritus professor of food science at Pennsylvania State University, took an unorthodox step for a nutrition researcher by expanding his investigation to include soil.
“We all say that healthy soil equals healthy people,” said Beelman, “but the truth is that we are still blowing smoke and we need to do more research to investigate this idea.”
“I got to wondering,” he added. “Have our modern agricultural practices been screwing up the fungal and bacterial populations in the soil to the point where the amount of (nutrients) in our diet has been compromised?”
To pursue this question, Beelman decided to focus on one antioxidant, l-ergothioneine — which he refers to as “Ergo.”
Several lines of evidence suggest that Ergo is an important nutrient for humans: Ergo deficiency might predispose us to inflammation and premature aging. Mushrooms, the fruits of fungi, are by far our best dietary source of Ergo, but it is also found in many plants, including oats.
Beelman teamed up with the nearby Rodale Institute, an agricultural research center in Kutztown, Pennsylvania, to trace Ergo from field to plate. First, they planted oats in the different farm plots, each plot under a different kind of experimental farm management.
“Tillage made the biggest difference,” said Beelman, jumping to the punchline. Tillage is essentially plowing without turning the soil over. For centuries, farmers have tilled to eliminate weeds, bury the remnants of old crops and prepare the ground for planting - but newer research suggests that disturbing the top layer of soil destroys microbial populations and contributes to soil erosion.
Indeed, oats grown in the “no-till” fields had 25% more Ergo than their counterparts in tilled soil, and the soil in the no-till field also had more Ergo. Beelman said he believes this is because tillage disrupts networks of bacteria and fungi.
Accordingly, Knight is involved in an effort to bank ancient soils — just as we are banking ancient seeds — so that these combinations of microbes are on hand to protect us at some future date when we are better equipped to understand how they work.