Carbon and corn

Atmospheric carbon dioxide concentration drops drastically during the corn growing season in the USA Midwest.  Corn, being a C4 photosynthesis plant, is an especially big consumer of carbon dioxide and today’s culture of planting high density crops, increases the consumption.  One estimate is that a field with 210 bu/A yield sequesters, per acre, about 3.6 tons of carbon is in stalks and leaves, 3.6 tons in roots and another 3.6 tons in kernels.  Obviously these actually vary per hybrid and environment but a corn field does tie up more carbon dioxide during the growing season than a tropical forest.  However, the roots and above ground foliage does return the CO2 as microorganisms digest the components.  If grain is processed through livestock, or humans, or ethanol it eventually also gets released. Although the forest trees delay the release for many years, eventually that carbon is also released as the wood rots or is burned.  Even in the forests where carbon is being deposited as wood, those deposits during the past are rotting by micro-organisms, releasing carbon dioxide.
 
Plants grown today consume carbon dioxide in today’s atmosphere and return it in a relatively short time.  Fossil fuel carbon was tied up a few hundred million years ago during a time of a warm and very wet earth. Some of that carbon did not cycle but, over time, the dead plant material was covered with deposits of sand and soil.  Use of fossil fuels are new contributions of CO2, beyond the recycled CO2 that is done by current plants. Recycling of current CO2 should not be confused with addition of CO2 from fossil fuels. Methane release from livestock is only part of the CO2 currently present and not contributing to the increase.  Ethanol produced from corn stalks or grain substituted for fossil fuel can reduce the addition of CO2 to our atmosphere.