Soil has the ability to store carbon, preventing it from entering the air as the greenhouse gas carbon dioxide and contributing to climate change. No-till farming and gardening—growing crops with little or no tilling or plowing—may be particularly well suited to sequestering carbon, especially when combined with organic practices.
Soil organic carbon (SOC)—carbon that derives from organic materials and is stored or sequestered in soil—accounts for approximately 58 percent of the total organic mass found in soil. It is the largest global pool of terrestrial carbon. But historic levels of soil organic carbon far exceeded modern-day levels. Globally, most agricultural lands have already relinquished approximately 50 to 70 percent of their initial SOC stores. This loss of SOC contributes significantly to the levels of climate-altering carbon dioxide in the atmosphere; approximately 792 billion tons of carbon emissions from 1750 to 1999 can be attributed to the loss of SOC. The depletion continues today, fueled by land-use changes and the regular plowing and tilling of agricultural fields.
When a field or garden is tilled, previously buried organic matter—including carbon—is brought to the surface and exposed to oxygen in the air. Oxygen is necessary for most soil microbes to digest carbon and other organic compounds. By bringing buried SOC to the surface, tilling accelerates the rate of decomposition and carbon dioxide exhalation.
Because no-till agriculture significantly reduces the frequency and severity of soil disturbance, early proponents believed the rates of carbon sequestration would far exceed the rates observed in tilled agriculture. But studies have not always supported this expectation. Jeff Moyer, farm director for the Rodale Institute near Kutztown, Pennsylvania, explains that conventional no-till agriculture rarely results in carbon sequestration. “Our research clearly documents that conventional systems are lucky to hold steady and not lose carbon over time, even under the best management practices.”
According to Moyer, the carbon equation changes dramatically for organic agriculture. “In organic systems, just the opposite appears to be the case; carbon is sequestered at greater depths in no-till systems than tilled systems. The extended root production, along with the increased soil macro- and microbiological life, sequesters the carbon deeper in the soil.”