More Than Dirt
Science is showing how healthy soil can help save the planet—and how we can all help improve what lies beneath our feet
Sunflower roots reach deep into the soil of a Kansas field, well tended for peak fertility. Another sign of soil health, plump nodules on the roots of a fava bean (right) nurture beneficial bacteria that aid plant growth.
EVEN THOUGH MULYSA MELCO HAS A DEGREE IN HORTICULTURE, she didn’t fully appreciate the life-giving handshake between plants and soil microorganisms until 2009. She and her partner, Michael, had bought an old house surrounded by compacted soil in Portland, Oregon, the year before. To improve the soil’s health, they began to prepare garden beds with sheet mulching to smother weeds and build organic matter. They also planted fava beans, winter peas and other “cover crops” to add nutrients to the soil and reduce erosion.
The following spring, when Melco examined her cover plants, she was dazzled by their knobby roots. Those knobs were nodules that nurture rhizobia, bacteria that pull nitrogen out of the atmosphere and convert it into fertilizer for plants, which in turn provide food and cover for insects, birds and other wildlife. “I realized there were all these participants in my garden,” says Melco, a landscape designer and horticulturist. “The plants, the microbes, the insects, the birds—they are all working together.”
Since then, Melco has intensified her efforts to nurture healthy soil. She crowds her 50-by-100-foot lot with 400 species of plants, including 70 edible perennials and 100 natives, knowing that each species offers a unique service to the soil microbes and the other living things in her yard. She also minimizes soil disturbance to keep the underground ecosystem intact, eschews garden chemicals, keeps the soil covered in live roots and converts weeds and other garden “waste” (she doesn’t think of it as waste) into either compost or mulch.
These steps are part of what’s increasingly becoming known as a soil-health approach—and the benefits abound. In Melco’s garden, new plants establish quickly, she rarely has a problem with insect pests and the influx of wildlife has been amazing. Melco and her family counted 10 species of birds in their garden when they first moved in but now spot 30. Among them: ruby-crowned kinglets, vireos, Wilson’s warblers and three members of the chickadee clan—mountain, chestnut-backed and black-capped—all flocking together. “The food-soil web is the foundation of this bigger picture,” Melco says.
Roots of an Empire
The use of cover crops—traditionally sown by farmers between market crops to protect bare soil from wind and rain erosion—is an agronomic practice at least as old as the Roman Empire. Today, the practice is making a striking comeback as more and more growers focus attention on the foundation of their empire: soil.
After decades of farming with the tools of industry—big machines, chemical inputs and high-tech seeds—many growers are doing everything they can to build the health of their soil with ecosystem-friendly practices such as reducing tillage, using herbivores for managed grazing and adding cover crops. In fact, the U.S. Department of Agriculture’s Natural Resources Conservation Service, which works with farmers nationwide, launched a soil-health campaign in 2012 with a simple message: “If you want your soil to be healthy, you shouldn’t see it very often. That’s because you want that soil to be covered all the time, preferably with living plants.”
Wisconsin farmer Ryan Stockwell took that message to heart. In 2013 he began planting cereal rye, daikon radish and other cover crops to enrich his soil and protect it from erosion, as conventionally farmed land in his region loses some 3 tons of soil every year. In the fall, while other nearby farm fields were bare and brown, Stockwell’s fields were a sea of green, hosting hundreds of migratory geese that stopped to rest and nosh before resuming their journey south. “Whenever I went out into the fields with a shovel, the birds watched and followed,” laughs Stockwell, the National Wildlife Federation’s senior agriculture program manager and a third-generation farmer. “It was a little Alfred Hitchcockesque.”
The results on his land are anything but scary. Stockwell says he has almost completely eliminated erosion, and his yields of corn, soybeans and wheat remain strong even though he has reduced fertilizer inputs by up to 30 percent. The improved soil also provides more resilience in the face of challenging weather. “When a wet spring hit two years ago, only a handful of my neighbors were able to plant crops,” Stockwell says. “Most didn’t plant and took a zero for yield. I may have seen a slight reduction in yield that year, but it certainly was a lot better than a zero. Because of that, I have far less stress with my farming.”
An Arkansas farmer checks a rye-grass cover crop planted to protect soil until spring planting. Leaving soil bare after harvest was one poor practice that likely worsened Dust Bowl devastation in the 1930s (above).
Symbiotic Soil Mates
Most of us instinctively feel that good soil is crumbly and rich in organic matter—what gardeners hope to find when they sink a spade into the ground. But many of us don’t realize that soil is only good when it’s healthy. That essential health derives from the complex interactions among plants and communities of soil microorganisms, including bacteria, fungi, nematodes and protozoa. Some scientists estimate that a teaspoon of healthy soil can hold more microorganisms than there are people on Earth. And according to the Food and Agriculture Organization of the United Nations, the living things in soil—from bacteria all the way up to moles—represent a quarter of the planet’s biodiversity.
Scientists have come to a relatively new understanding of the symbiotic relationship between plants and this vast array of soil microbes. Simply put, plants use the sun’s energy to pull carbon dioxide out of the air and create a carbon-rich syrup to fuel their own growth, tossing off oxygen as a waste product. Plants only use part of this carbon syrup, however. About half can be strategically leaked as exudates through the roots to feed soil microorganisms.
To pay for the calories the plants supply, microorganisms bring plants nutrients that they’ve extracted from the mineral portion of soil—the rocks, sand, silt and clay. In addition, a community of plants is connected by an underground network of beneficial fungi that share water, nutrients and carbon—life’s chief building block—among the plants.
“Underground, there is this other world, a world of infinite biological pathways,” says University of British Columbia forest ecologist Suzanne Simard, who describes how the underground network among trees allows a forest to “behave as though it’s a single organism.” Indeed, Simard and her students have shown that Douglas-firs and paper birch pump carbon back and forth through a fungal network during the seasonal times when they need it most.
Plants can use fungal networks to sound an alert when ravaged by pests, sending out a warning through the silky fungal hyphae that an attack is underway. They can also call up an underground army to defend them against pests. Scientists have studied how citrus, corn and strawberry plants, for example, all release volatile chemicals underground when insects attack their roots, attracting tiny soil nematodes that feed on those insects. Without healthy soil, none of these protective interactions could occur.
The vigor of life within the soil can even impact surface biodiversity and the composition of ecosystems. A 2016 study in Nature Plants, for example, found that a transfer of soil microorganisms from healthy ecosystems can help restore degraded landscapes and even determine what kind of plant communities will take hold and flourish. When the researchers put soil microorganisms from grasslands into a restoration area, the vegetation in the restored area became more like that found in grasslands. When they used microorganisms from heaths, the plant communities were more like heathland vegetation. So the dirt below can determine the plants above.
A soil bacterium, soil mite and spores of Penicillium (clockwise from bottom left) hint at the vast array of life thriving in the rhizosphere—the world where roots and microorganisms mingle in beneficial symbiosis. One teaspoon of soil holds billions of such creatures.
Why Air Needs Soil
All the action belowground can also have a profound impact on the air we breathe. Plants pull carbon from the air and pump it into the soil with their exudates. Soil microorganisms eat it and store it in their own bodies. In effect, then, soil serves as a carbon storehouse, Earth’s largest terrestrial carbon sink.
Unfortunately, the world’s soil has lost one-half to two-thirds of its carbon in the centuries since agriculture began, according to soil scientist Rattan Lal of The Ohio State University. That’s billions of tons of carbon released into the atmosphere. Tilling, leaving the ground bare during fallow periods, installing monocultures, reducing landscape biodiversity, heavy chemical use—all such practices disrupt communities of microorganisms and allow soil carbon to volatilize and become atmospheric carbon, where it contributes to global warming.
Climate experts agree that our only hope for combatting climate change is to cut fossil fuel emissions and reduce the load of carbon dioxide already in the air. Some of that excess carbon can be put back in the soil by enhancing the healthy interaction between plants and underground microbes. “There’s a growing recognition of soil’s role in the carbon cycle and its importance in combatting climate change,” says Bruce Stein, NWF’s associate vice president of conservation science. “Reblacking the soil [i.e., increasing soil carbon by building soil health] offers a great opportunity for addressing the problem.”
Long discussed by scientists, this idea caught on at the 2015 global climate conference in Paris, where 33 countries and 140 other groups pledged to build carbon in agricultural soils by 0.4 percent per year. Proponents say that rate will help stop the rise of atmospheric carbon and also reduce food insecurity by making soil more productive.
In a thawing Siberia, permafrost is melting as temperatures rise, exposing roots, toppling trees and releasing tons of soil-stored carbon into the atmosphere. Restoring soil’s role as a carbon sink may help heal the planet.
In Defense of Dirt
Clearly, the soil-health approach confers a multitude of benefits: higher production, more resilience in the face of extreme weather, cleaner air and water, carbon sequestration and enhanced protection of biodiversity. “If you care about wildlife, then you have to care about not endlessly expanding the agricultural footprint,” says Stein. “The key is to treat the soil more respectfully and enhance its productivity.”
All of us can help in this effort. We have gardens, lawns or neighborhood parks, all of which can benefit from the soil-health approach. We may think the word “ecosystem” only applies to pristine wilderness areas, but we are part of an ecosystem wherever we live and need to focus on helping it remain healthy. Wherever we are, that begins with soil.
Tips for Healthy Soil
The National Wildlife Federation’s Garden for Wildlife™ program offers valuable advice on how to transform your garden into a haven for wildlife while also nurturing your flowers, fruits, vegetables and soil. To learn more, go to www.nwf.org/
sustainablegarden, and try these simple tips to improve soil health:
Minimize bare dirt. Instead of leaving your soil bare in the off season, install legumes, grasses or other cover crops that will prevent erosion and add organic matter and carbon to the soil. During all seasons, mulch between plants and leave twigs and leaves on the ground to protect soil and provide food for beneficial soil microorganisms.
Do not disturb. Each time you churn soil, you’re disrupting the habitat created by billions of microorganisms. The less disruption, the better.
Avoid chemicals. Pesticides and herbicides can kill indiscriminately, alter the food web in your garden and harm beneficial pollinators and birds. Chemical fertilizers can interfere with the natural feeding relationship between plants and soil microorganisms.
Don’t use peat. Peat comes from fragile bogs that need protection, so use locally sourced soil additives such as farm manure, wood waste or leaf mold.
Make compost. Toss kitchen scraps, old leaves, prunings and just about anything else organic from kitchen or yard into a composter to build a rich mix that will help soil thrive and provide habitat for native organisms. This reduces waste in landfills, too.
NWF at Work
Hand in Hand with Farmers
Because agriculture has a huge impact on wildlife habitat and water quality, the National Wildlife Federation advocates for strong conservation provisions in the Farm Bill and funding to help farmers implement practices that protect soil, improve water quality, minimize chemical inputs and provide wildlife habitat. Through its Cover Crop Champions program, NWF has enlisted more than 60 farmers to teach others about planting cover crops and adopting other practices that aid ecosystems. To date, these champions have talked with more than 28,000 farmers across the Upper Midwest.
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Oregon-based writer Kristin Ohlson is author of the book The Soil Will Save Us.
More from National Wildlife magazine and NWF