Most conversations about climate change focus on fossil fuels and rightly so, for the combustion of coal, oil, and natural gas are responsible for two thirds of carbon emissions. Increasingly, however, scientists, environmentalists, and policy makers are linking climate change to the health of our soils, with implications for everyone from large-scale farmers to backyard food gardeners.
In addition to being a necessary medium for plant growth and health, soil is an enormous carbon reservoir, containing more carbon than the atmosphere and all plant life combined. Carbon enters the soil through a complex cycle that circulates carbon molecules between the earth, ocean, plants, and atmosphere. Carbon dissolves into water vapor and sinks into the earth with each rain. Through photosynthesis, plants pull carbon from the air and transform it into carbohydrates to use for energy. Plants send excess carbohydrates down to their roots and into the earth to feed the soil organisms upon which they depend to access nutrients and fight disease. When these organisms consume carbohydrates, as well as carbon found in water and in dead vegetation, they lock carbon into the soil, preventing it from oxidizing back into the air as carbon dioxide or running off with the rain.
Together, the actions of plants and soil organisms cause soil to absorb more carbon from the air than it releases, regulating the amount of greenhouse gases in the atmosphere. Human activities, however, have interfered with this carbon cycle. Deforestation and the destruction of grasslands have removed the earth’s protective covering of vegetation, exposing soil to the air and accelerating the oxidation of carbon into carbon dioxide the atmosphere. Modern agricultural practices have been equally damaging. In particular, mechanical tilling has also exposed soil carbon to the air and, along with artificial fertilizers and pesticides, has reduced the populations of soil organisms and, therefore, the ability of microbes to lock carbon into the soil. As a result, over the course of the last hundred years, soils have lost 50 to 70% of their carbon stock, accounting for a third of carbon dioxide emissions.
Fortunately, this process is reversible, but in order to replenish the soil’s carbon stock, we must not only replant our forests and grasslands. We must also change how we grow our food so that, instead of depleting the soil of carbon and life, our agricultural practices replenish the soil’s carbon stock and nurture soil organisms. Farmers as well as home, school, and community gardeners can be part of this regenerative soil movement. To reduce oxidation from the soil, we can integrate our gardens with trees and shrubs, a practice known as agroforestry. Rather than artificial fertilizers, we can feed our crops with compost and cover crops. Instead of plowing our fields and beds, we can let plant roots and soil organisms loosen the soil, a process known as biological tilling. Instead of using artificial fertilizers, we can manage pests by integrating our gardens with plants that attract beneficial insects.
None of these efforts will halt climate change if humans do not also decide, individually and collectively, to simplify our lives and reduce our consumption. Nonetheless, widespread adoption of restorative agricultural practices could mitigate climate change by reducing atmospheric CO2. Because carbon-rich soils resist erosion, hold more water, and produce more crops than soils that have lost their carbon stock, restorative agriculture could also help us adapt to climate change and move towards a more food secure community. We hope that, by adapting restorative food growing practices, you will make small changes towards the health of our soil and our planet and help reform our food growing culture.