The most valuable portion of any agricultural soil is the various carbon compounds contained therein. Plants live as a part of an ecological community and much of it revolves around the microorganisms that live in and on the carbon in the soil. Carbon compounds in the soil not only sequester carbon, but they also provide an incredible value in terms of soil fertility, supporting soil organisms, soil chemistry, water retention, and a million other things. We live in a world where nearly all soils are heavily degraded, so how do we improve the amount of carbon in the soil? There are two ways that carbon gets into soil: decomposition of organic matter and the liquid carbon pathway.
Decomposition of organic matter is pretty much exactly what it sounds like. Leaves, wood chips, food waste, manure, etc. are broken down into compost. As these materials break down, they support communities of organisms that specialize in breaking down the bodies of formerly alive organisms, be they wood, fungus, leaves, or even manure. After all, what is manure if not the bodies of something previously alive that has a head-start on decomposition through the process of digestion? The process of decomposition takes many steps as each organism breaks down the component pieces a little more than the last. What is left is compost, an incredible soil amendment that adds healthy biology and nutrients to the soil. The problem with compost is that it isn’t very stable long-term. While the finished compost breaks down slower than the components that went into the compost, it will still continue to break down until it is eventually gone.
The liquid carbon pathway is a relatively recent term for a process that has been happening for close to half a billion years. Plants need certain conditions in the soil they inhabit, and they need access to vital nutrients to grow and maintain health. They use the energy from the sun and carbon dioxide from the air to create sugars. From those sugars, combined with nutrients from the soil, they make a huge variety of compounds that they use to build their bodies. But they do so much more than just build their bodies. They also create a whole complex of root exudates that they inject into the soil through a process that has come to be called the liquid carbon pathway.
The area within a millimeter or two of the living roots is called the rhizosphere. The rhizosphere hosts a community of living organisms that is different than the organisms found in the rest of the soil and in decomposing organic matter. Largely, these organisms are supported by the root exudates of the plant, and, in turn, support the needs of the plant. Mycorrhizal fungi is a big part of the makeup of the rhizosphere, but there are also a number of bacteria and other microorganisms that thrive in that zone, creating the right conditions for the plants and benefiting from the root exudates.
It isn’t just the beneficial organisms that make this zone important to the soil, though. There are also things that happen here to the soil chemistry. The mycorrhizal fungi work with the plants to create glomalin, which is a long-lasting soil protein. Another family of compounds produced are call MAOCs, or Mineral-Associated Organic Carbon. MAOCs are formed directly by plant exudates, where the compounds excreted by the plant roots bind to minerals in the soil, creating another form of stable soil carbon.
The interesting thing about these chemical forms of organic carbon is that, for some reason, organic carbon that is produced through the liquid carbon pathway is much more stable in the soil than the carbon that is produced through decomposing organic matter. Glomalin can last 4 decades or more in the soil. Many other compounds produced in this way also have incredible staying power in the soil. Organic matter from decomposing matter typically burns off completely in just a few years.
In the age of industrial agriculture, stable soil carbon is a declining resource. Our system of plowing, fertilizing, and using biocides all destroy the soil carbon that the plants rely on to grow. If we want our system of food production to be sustainable, we need to find ways to sustainably replace the carbon that is produced through the liquid carbon pathway. The conventional wisdom is that it isn’t a renewable resource on a human timescale, meaning that if we create the conditions needed to repair the carbon in the soil, it will take decades or more to return it to the soil health we want. So we invented regenerative agriculture to repair the soil. And we add compost, because it helps.
But there is hope. The compost that comes out of a LEHR Garden is created not just from decomposing organic matter, though that is part of it. A LEHR Garden decomposes wood chips while the plants grow in it. Those living plants create not just a viable liquid carbon pathway, but an incredibly active one. Glomalin is a good indicator that there is an active and effective liquid carbon pathway. The glomalin produced in one year exceeds any amount found after decades of accumulation anywhere in California, according to one study. And that glomalin can be produced in large quantities as an output. There’s still a ton of science to do, but there are high hopes that we may be that much closer to a solution.