Cover Crops, Carbon Sequestration, and the Future of Carbon Markets
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ot many days go by in the agriculture industry today before the words sustain- ability, cover crops, carbon sequestra tion, and carbon markets are heard in the news, industry meetings, and local coffee shops. The new presidential administration’s focus on climate change and desire to reduce carbon emissions has resulted in an increased interest in how production agriculture could potentially help in reducing carbon dioxide emissions. Many people are talking about “potential” carbon markets and the “potential” positive environmental impact, however, there is significantly less discussion about the carbon cycle and the mechanism by which soils can be a sink for atmospheric carbon via the use of cover crops. No matter what ones views are about climate change, it is important to fully understand what is known today versus what is not really understood. Carbon dioxide is the molecule driving most of this conversation. Carbon dioxide is made up of one carbon and two oxygens. Therefore it is imperative to fully understand the carbon cycle to truly understand the potential of utilizing the soil as a carbon sink. Carbon is an essential plant nutrient that is utilized by plants in the form of carbon dioxide from the air. Carbon dioxide is required by plants to complete photosynthesis. The following quote from the 13th Edition of The Nature and Properties of Soils sums up why there is so much discussion around carbon markets: “Since carbon dioxide is a major cause of the greenhouse effect which is believed to be warming the earth’s climate, the balance
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Ag Mag THEAGMAG.ORG
BY DEREK EMERINE
between accumulation of soil organic matter and its loss through microbial respiration has global implications. In fact, more carbon is stored in the world’s soils than in the world’s plant biomass and atmosphere combined.” There is no debate that once tillage begins, about 50% of soil organic matter is lost within 20 years of continuous tillage. There is also no debate that there has been a significant reduction in organic matter levels across the United States since the agricultural revolution. As a result, there are many entities interested in utilizing the soils’ ability to capture atmospheric carbon from excess carbon dioxide in the atmosphere. On the surface this makes sense, but the complexities of the carbon cycle show that this endeavor is not a simple as many suggest. The diagram outlining the carbon cycle illustrates some of the difficulty in fully utilizing the soil as a carbon sink. There are four yellow arrows that illustrate carbon dioxide being released into the atmosphere versus one red arrow showing carbon dioxide being removed from the atmosphere by plants to perform photosynthesis. Carbon dioxide release into the atmosphere comes from fossil fuel combustion, plant and animal respiration, and carbon dioxide release from the soil. The first three are discussed more often than carbon dioxide release from the soil. Carbon dioxide release from the soil can come about in few different ways including any form of tillage that exposes soil organic matter to oxygen, organic matter oxidation, oxidation due to poor soil structure or aggregate stability, and respiration from soil microorganisms.
