Soil: The Secret Weapon Against Climate Change

Understanding nature’s carbon cycle can help us restore balance to the planet.

By Kristin Ohlson

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a handful of healthy soilIt’s a shame to quash the hope and high spirits of spring with bad news, but there it is: The U.S. Global Change Research Program just released the Third National Climate Assessment, which concludes that climate change continues apace, that human activity drives it, and that it is already affecting every part of the country with drought, flood, and heat waves.

But there is more good news, happening far away from reports and government agencies. Out of the headlines, ordinary people—from those commanding thousands of acres to those with a small yard or even a plot in a community garden—are building the health of their soil. As their soil gets richer and darker, they are performing climate-change-mitigation magic: removing carbon dioxide from the air and stashing it in the soil as life-giving carbon.

These people (and you may be one of them without knowing it) do this by bolstering the ancient partnership between plants and soil microorganisms. Plants stretch out their leaves and capture carbon dioxide, then convert it into a carbon-rich fuel for their own growth. But they also send up to 40 percent of that carbon fuel down to their roots to feed the incredibly dense and diverse community of soil microorganisms under our feet—some 6 billion in a tablespoon. Plants don’t share this elixir of life freely, though: The soil microorganisms make a payment in essential minerals that they extract from rock. The plants prosper and grow with these nutrients, and the soil microorganisms carry on their own business underground, concentrating that carbon into increasingly less volatile forms.

Over billions of years, this exchange between plants and soil microorganisms created our lush planet. Then humans evolved and multiplied, first as hunter-gatherers and then, beginning about 10,000 years ago, as agriculturalists. With that transition, we started to interfere with the way carbon cycled from the atmosphere into the soil and back again. We burned down forests to create farmland and ripped open the soil—allowing soil carbon to volatilize into carbon dioxide—to plant seeds. Some scientists believe that these and other agricultural activities warmed our planet so much that we avoided another ice age that should have occurred 2,000 years ago. The vast chemical-drenched monocultures of industrial agriculture are the most extreme disruption of the carbon cycle, not only accelerating global warming but also polluting water and air, destroying the land’s resilience in the face of drought and flood, and creating piles of nutrient-depleted food.

We didn’t intentionally screw up the carbon cycle, of course—this understanding of the partnership between plants and soil microorganisms and the impact it has on climate is quite new. The people who are running with this new understanding are seeing the health of their soil and plants rebound, as well as taking extra satisfaction in knowing they’re helping to restore the carbon cycle. The trick is to mimic nature’s ways in our farms and gardens in these three basic ways.

Do not disturb. We like to think we’re “standing on solid ground,” but there’s constant movement down there! Soil microorganisms use the carbon obtained from plants to make glues that cement particles of dirt together, both to create tiny protective habitats and to hold water. When we dig and till, we shatter these structures as well as break up massive networks of beneficial fungi. Many farmers now avoid damaging this underground infrastructure by switching from plowing to no-till agriculture, in which a machine makes a tiny slit in the soil instead of a furrow. In the same vein, home gardeners don’t turn the soil over. Instead they loosen the top layer of the soil with the biological activity encouraged by heavy mulching and use deep-rooted annuals to ease deeper soil compaction. When they plant, they make small openings for seeds and new plants—much as modern surgeons make tiny incisions instead of opening someone all the way up.

Build density. Nature abhors a vacuum. You already know this if you’ve tried to keep a patch of bare soil weed-free for more than a few days. When we clear away vegetation and expose the ground to the air, we’re not only encouraging soil carbon to volatilize and drift away as carbon dioxide, but we’re also removing carbon’s pathway from air to soil through plants—photosynthesis can’t take place on bare ground—and starving the soil microorganisms underneath. Farmers aware of this connection plant cover crops between rows and on fallow fields to protect and feed the soil, and they never clear away crop residue. Home gardeners try to make sure that every inch of soil under their care has roots in the ground or a heavy mulch of dead plant material—even the latter will keep the soil microorganisms in business.

Boost diversity. Nature also abhors monocultures, which is why it sends pathogens and pests to strike down clusters of the same plants grown in the same location, year after year. Diversity above and below ground is best: A variety of plants above feeds a smorgasbord of carbon fuels to the microorganisms below, which in turn offer a greater variety of nutrients to the plants. Crop rotation has long been a pillar of organic agriculture, but some farmers are now planting “cover crop cocktails” with a dozen or more different plants to feed the soil microorganisms as well as thwart pathogens. Home gardeners can achieve this same effect in borders planted for maximum biodiversity and density—small trees, shrubs, perennials, fall and spring bulbs, and annuals, together keeping the soil covered and each contributing their unique carbon fuel to the microorganisms below. Same with our vegetable gardens: Mix up varieties and sow by the square foot rather than the row. Even our lawns (the nation’s largest irrigated crop, occupying three times as much space as corn) can be decent ecosystems when we use seed mixtures containing several varieties including clover, which provides nitrogen to the grasses, and avoid chemical fertilizers, which disrupt the partnership between plants and soil microorganisms.

It’s hard for an ordinary person to know what to do in the face of troubling climate news, but the new science of what’s going on underground gives new hope. We have powerful allies in our plants and soil. Even if our garden or yard is small, we can work with these allies to pull carbon dioxide from our atmosphere and pack it back into the soil where it belongs.

 

To buy The Soil Will Save Us and to learn more about how scientists, farmers, and foodies are healing the soil to save the planet, visit kristinohlson.com

The Soil Will Save Us

 

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