Carbon has a bad press. There is too much in the atmosphere and the Earth is heating up. Driving a car, buying a TV, even blowing our noses, are cause for concern about our “carbon footprint” — the burden each activity and purchase puts on the environment. New laws say that carbon is to be taxed and traded like a toxic asset. It is the bad stuff spoiling our weather and worrying our children.
Can this be the same substance that sparkles in a diamond, that makes the pencil line in a notebook, that structures the cells of our bodies? Look around you — everything that is not metal, stone, glass or ceramic has carbon as part of its essential makeup; that includes the sheetrock on your walls and the plastic of your computer. We are carbon-based life forms, living in a carbon world. Carbon is the element of life.
The Carbon Dilemma
So how should we solve the dilemma of good and bad carbon? They say a weed is simply a plant in the wrong place. Too much carbon in the wrong location, the atmosphere, is like a gardener’s nightmare – weeds run amok. In the world garden, can more carbon be planted in the right place where it is both useful and constant?
A natural home for carbon is in all living beings, vegetable, animal and human. When an organism dies, that carbon can be transformed or sequestered. Gaia, the self-organizing principle of our biosphere, has found many creative ways to hide away excess carbon. The ocean are littered with the shells and dead bodies of invertebrates and lined with coral reefs; these are forms of carbonate that lock away vast quantities of carbon
Until recent times, the fossilized remnants of vegetation lay hidden deep in the earth as coal, oil and natural gas. Human activity oxidizes those hydrocarbons discharging carbon dioxide into the air. In a similar way, over the last 100 years industrialized agriculture has used up over 50% of the essential carbon in the topsoil. According to the Rodale Institute, 1.5 trillion pounds of CO2 are released each year by US agriculture through unsustainable cultivation methods and the overuse of nitrogen fertilizer.
We are breathing the carbon we should be cultivating. Carbon has to be replanted in the soil where it belongs.
Carbon in the Soil
Carbon is a master of transformation. In the soil, it takes a myriad of forms. Plants are built of carbon-based cellulose and their life-blood contains carbohydrate sugars. As plant material decomposes, it gives off carbon dioxide. A little heavier than air, CO2 flows close to the soil surface and is breathed in by the stomata on the underside of leaves. In a healthy ecosystem, little CO2 gets released into the atmosphere; the carbon is recycled back into plant bodies.
Millions of species of living beings work the carbon in the soil. They eat and are eaten, digest and excrete, reproduce, live, die and decompose, forming a web of life that transmutes and transforms carbon in unimaginable ways. One of the outcomes of all that activity is a stabilized form of carbon called humus.
Humus is the essence of fertility. It is the earthy smelling stuff that makes soil dark brown. Unlike decomposing organic material that is in flux, humus can last in the soil for centuries. Surprisingly, not that much is known about humus. It is an exceptionally complex spongy jelly-like substance that binds carbon into different geometric forms.
Humus is porous and not only holds water but also provides accommodation for billions of microbes. Of course, the bodies of bacteria, archaea and fungi are themselves composed of carbon, so the humus does double duty in sequestering carbon. We gardeners know it as a magic ingredient of the soil – it gives and holds life.
Humus is not the only form of soil carbon. Some decades ago, soil scientist Sara Wright discovered a sticky soil protein that contains 30%-40% carbon. She named the substance glomalin, not simply because it is like a superglue that ‘gloms’ soil particles into aggregates, but because it is created by the Glomales group of mycorrhizal fungi.
Glomalin is now recognized as an essential component of fertile soil that can remain stable for up to 40 years. It gives soil tilth, the bobbley texture that tells you your soil is full of life and health. The arbuscular mycorrhizae that create glomalin are symbiotic with plant roots, transporting nutrients in exchange for the carbohydrate sugars in sap.
Root, fungi and glomalin form a powerful micro-ecology that transforms and holds billions of tons of carbon in healthy soils. Research shows that as atmospheric CO2 levels rise, the mycorrhizae work harder to gather up the carbon and hold it securely. However, the fine hair-like fungal hyphae are easily destroyed by conventional cultivation and are intolerant of high levels of phosphate. As the farmer plows and scatters fertilizer, the fungal soil web is broken; the marvelous sticky glomalin evaporates into the air.
We think we understand soil, but 1500 years ago the Amazonian people knew secrets we are only now rediscovering. They were able to create a rich fertile self-renewing soil called terra preta or dark earth. Terra preta is man-made, constructed from organic matter, human and animal waste, pottery shards and, surprisingly enough, ground up charcoal.
The Amazonian dark earth contains upward of 9% black carbon, produced from biochar the slow burning of wood and leafy materials at low temperatures. At first glance, this might seem to add CO2 to the atmosphere, but slow burning does not oxidize the carbon in plant cellulose; it keeps it in solid form. Somehow, this ancient civilization found a way to sequester more carbon in the soil that we ever thought possible.
A surprising feature of this soil is that it grows at a rate of 1 centimeter per year. The cause is an extraordinarily rich ecology of soil life. The pores of the charcoal are an excellent home for microbes and, the biochar rather than being inert, actually increases the activity of the mycorrhizae that make glomalin. Terra preta has 70 times more carbon that the surrounding soils. Maybe it is time to relearn these ancient growing techniques.
We hear news about the effects of global warming – the Arctic icecap is melting, the oceans are rising, hurricanes are increasing in severity. We are told we can help by reducing our use of hydrocarbons — but can we do more?
Gardeners, growers and farmers are gatherers, transformers and shepherds of carbon. Every plant captures carbon; every acre of healthy soil holds thousands of pounds of carbon out of the atmosphere. If US household cultivated their gardens organically, adding plenty of compost and strengthening soil life, over 10% of the worlds CO2 emissions could be offset. Growing plants and tending the soil is more than a pastime; it is part of our task to help keep carbon in its right place.