As for the second, carbon sequestration, or pulling carbon out of the air and storing it deep in the ground, as noted environmental journalist Elizabeth Kolbert points out in a recent article, no one knows how to do this.
|So far, technology-based carbon capture and sequestration hasn't panned out|
But what about the rest of us?
My yard is much smaller than the typical ¼ acre suburban plot; my garden encompasses about 2,000 square feet, smaller than many houses. Most people in the US and elsewhere live in similar urbanized areas. Large-scale carbon sequestration on vast acreage, as potentially could be practiced by farmers (some two percent of the US population) is beyond reach. We regular folks are left with yet another situation where direct-action participation in solutions to the climate disruption problem might seem impossible. Most of us aren’t off-grid homesteaders; we rely on the local utilities and pubic services; non-existent public transit might force us to drive even if we’d rather not; and other realities of our everyday lives might prevent us from doing as much as we’d like. Even if we can imagine what is necessary to be done, and are prepared to help decarbonize our society, we might feel powerless, possibly unable to take positive, rewarding action to help remedy the situation.
Yet we can do something. Quite a lot, actually. For the first part, we can consciously reduce our lifestyles and become actively civically engaged; for the second, we can practice backyard carbon sequestration by becoming carbon gardeners, ourselves, and in the company of others. I agree with those that argue that unless there are mass movements and unless governments and corporations change their ways, individual changes won’t mean that much. However, I also believe that the butterfly effect is just as real in human systems as in earth systems, and in fact, backyard soil carbon storage works in both at once.
Thus I say, again, strongly, to everyone who is in charge of caring for a backyard, front yard, side yard, or some other patch of ground where plants grow, soil carbon sequestration is something you can do, on your own, fairly easily. You will have to give some things up, such as synthetic fertilizer, but rather than feeling deprived, you will be helping create abundance.
|We can help nature do the job|
Now when it comes to deep carbon storage, anyone practicing various forms of ecological gardening, organic gardening, permaculture or bio-dynamic gardening is already at least part way there: carbon sequestration is part of everyday practice. However, in the US at least, as with regenerative farmers, permaculturalists and other gardeners of their ilk are few and far between. Even if you add the daily growing host of wildlife, native plant, and pollinator gardeners, the needed acreage is not increasing quickly enough. And because most of these folks are not explicitly gardening for carbon sequestration, there are still things they can learn. Though for many, all that’s required, perhaps, is some new information, a shift in perspective.
What every would-be carbon sequestration DIYer needs to know
Compost doesn’t store carbon. Like other ecological gardeners, I know that having a healthy soil biome is very important in all kinds of ways. I’ve always made compost and added it to my beds, and also use it to top dress my polyculture lawn. It's vitally important because it helps plants grow better, without the need to add synthetic, inorganic fertilizer. I’ve also known that it’s important to provide lots of organic matter because the soil critters—the fungi, bacteria, arthropods, nematodes and so on, utilize that organic matter and in turn, convert it into nutrients plants can use. In just one example, most gardeners know that the nitrogen-fixing bacteria that colonize the roots of legumes such as clover can convert nitrogen from the air into a form plants can use (one reason it’s good to grow clover in your lawn). However, healthy soil also contains free-living soil bacteria and other microbes that do the same thing. In my yard, more organic material gets added in the form of grass clippings left in place, and fallen leaves left under bushes and trees to develop naturally into duff. Organic mulch is also helpful, in terms of protecting the soil and helping provide nourishment to the soil critters. I can confidently say that my soil has plenty of organic material, especially in the areas that are planted with native prairie plants: they are deep rooted, and approximately 1/3 of the roots die every year, providing even more organic matter for all these critters to live on.
So far so good. However, what we are after is deep, stable carbon. And that is not provided by the process of breaking down of plant residues, manure and the like into compost or incorporating organic material into the soil. Strictly speaking, that catabolic process releases CO2 into the air as the decomposers and other critters access nutrients. What is needed is the creation of humus: we want to foster the relationships between actively growing plants, fungi and soil microbes and all the other critters that build soil. It is humification that, as topsoil is built, stores carbon at a deep level and in a stable form that can stay in storage for hundreds of years, as long as it is part of a healthy ecosystem or good soil nurturing methods are used.
Humification stores carbon and depends on actively growing plants. How does this work? Very briefly, here is what happens. While plants are growing, they pull carbon dioxide out of the air (and absorb water through leaves and roots). During the complex process of photosynthesis the CO2 breaks down into oxygen, which the plant releases into the air, and carbon, which gets combined with water and converted into the carbon sugars the plant uses to fuel itself. However, something else happens to the carbon sugars, which might, intuitively, seem counterproductive. Some of this “liquid carbon,” as Australian soil scientist Christine Jones calls it, travels down to the roots, and, as it fuels their growth, a portion leaks out of the roots into the soil. Why would this be? It would seem inefficient, like the leaky faucet in someone’s bathroom that wastes water and increases the owner’s monthly bill.
The answer is that, like canny traders, plants use the liquid carbon, or “root exudates,” as a kind of exchange medium, which they trade to mycorrhizal fungi, bacteria and other microbes not only in return for nutrients such as nitrogen (those free-living bacteria get their own carbon fuel by living in association with growing plants) and phosphorus, but also the wide range of other nutrients plants need to help fuel growth. In fact, in healthy soil plants get 85-90% of nutrients they need through this carbon exchange. In the process, vast networks of mycorrhizae form in the soil, connecting plant roots with nutrients they couldn’t otherwise access. Unlike with the water waste and higher bill, plants don’t seem negatively affected by this loss of carbon sugars. Rather, the more mycorrhizae and microbes there are getting fed, the healthier the soil and the healthier the plants.
What happens to the carbon sugars: how does the humus build?
The story doesn’t end there. The mycorrhizae themselves, having utilized the carbon sugars and supplied plants with nutrients, also practice exudation: in this case a gluey, sticky protein called glomalin. With other gums and glues produced in the carbon-nutrient exchange, glomalin aids in the formation of soil aggregates by sticking together particles of sand, clay and silt into the larger clumps that that collectively we call humus, which is where the real carbon storage action is. Glomalin is thirty to forty percent carbon and is incredibly stable and long-lasting. Soil high in humus is soil that is storing carbon—humus is about 60% carbon. It’s only since 1996, when Dr. Sara Wright described glomalin and its role in humus production, that we have been able to accurately measure the carbon being sequestered in soils, so we now can assess our carbon-storage efforts. As important as carbon storage, however, is the effect soil aggregation has on nitrogen: the aggregates that form humus also enable nitrogen-fixing bacteria to function, enabling plants to get more of the nourishment they need.
As long as there have been gardeners, humus has been appreciated, since its presence happens to guarantee that soil is fertile and has good tilth—it has plenty of texture: porous, “fluffy,” with air pockets, room for water penetration and good water holding capacity, among other virtues. Soil in good tilth often looks a little like “black cottage cheese,” as farmer Gabe Brown has described it: it doesn’t pour through your hands like sand or break into large, hard chunks like clay. Humus isn’t something you can separate out of the soil. Structurally it is the soil, woven throughout the way novelist Henry James once described meaning and symbolism being woven into a novel like the design in a carpet. As every good gardener knows, humus-rich loam is the best medium for growing flowers or vegetables. What is new is the discovery of the relationships that build humus and how all that carbon gets stored—and also what disturbs the system.
Barriers to carbon storage
|1% Carbon on left; 5% Carbon on right|
|Carbon sequestration happening here|
We can all be carbon gardeners
So, what to do? How can we actively foster all the biological relationships that build up the carbon reserves in our gardens and by so doing, building resilience into the soil system, thereby helping build resiliency into earth systems and our human society? In part two, I’ll discuss practical methods for turning a backyard into a carbon sink.
- A lecture by carbon farmer Gabe Brown on You Tube
- A great interview with Dr. Christine Jones in ACRES magazine
- NRCS Webinar: The Environmental Benefits of Organic Agriculture: Soil
Compost by Any Other Name
The Polyculture Lawn, a Primer