“Agriculture contributes 33% of all the emissions of the world. And we can’t get to net zero — we don’t get this job done — unless agriculture is front and center as part of the solution.” So says John Kerry, President Joe Biden’s climate czar, in a video shared on the social media platform X (formally Twitter).
As I said many times before, no one outside of agriculture seems to understand the carbon cycle as it relates to agriculture. Even when “industrialized,” I’ve argued that corn is a net carbon sink, and a huge wealth generator for the economy.
Using the 160 bushel corn crop I used in a previous article, how much CO2 is cycled through the corn plant and into plant and animal tissue (including humans), and into the soil through roots and fodder?
The CO2 molecule contains one atom of carbon and two of oxygen.
A barrel of crude oil weighs approximately 300 pounds. The rule of thumb is you multiply the weight of a fuel by 3.15 to calculate the amount of CO2 that will be produced when burned. Therefore, burning a barrel of oil will result in 945 pounds of CO2 released to the atmosphere. Reversing that means photosynthesizing the energy equivalent of a barrel of crude oil removed 945 pounds of CO2 from the atmosphere.
In that previous piece, we learned a 160 bushel corn crop can capture, net of respiration, the energy equivalent of 21.3 barrels of crude oil. That amounts to just over 10 tons of CO2 removed by one acre of corn. Applied to 90 million acres means, theoretically, the U.S. corn crop can remove 900 million tons of CO2 from the atmosphere, incorporate 243 million tons of carbon into plant tissue, and release 657 million tons of oxygen into the atmosphere. It took the equivalent of 1.2 barrels of fossil oil energy per acre to grow the corn, for a total input of 108 million barrels, which, if all that energy came from fossil fuel (some would have been electrical energy supplied by hydro, wind, solar, or nuclear) would have released 52 million tons of fossil CO2. Net CO2 removed, then, would be 842 tons. The carbon removed and incorporated into plant tissue would be 277 tons, and the oxygen released from its carbon bond would be 615 tons.
Most of the 842 tons of captured carbon will eventually be returned to the atmosphere. In 2020, 27 percent of the crop was converted to ethanol, mixed with gasoline, and burned in cars. Nearly 40 percent was used directly as feed, and an additional 7 percent was fed as distiller’s grain, a high protein byproduct of ethanol production. Some of the carbon fed to ruminants will be returned as methane, a climate warming chemical 80 times more potent than CO2. But methane, CH4, eventually degrades to CO2 and water.
As there have been ruminants of some kind (buffalo, deer, elk, antelope, wildebeests, camels, etc.) consuming grass and belching methane for thousands of years, adding to the historic load of methane in the atmosphere from animals in the present age is likely minimal to none. Remaining uses were 17 percent for exports, and 9 percent for human food and industrial uses.
The above uses are all from the grain portion of the crop. The fodder and roots account for 55 percent of the CO2 captured, or 495 million tons (0.55 times 900). About 90 percent of that tonnage will be returned to the atmosphere in a few years. The 10 percent balance will become humus, which decays so slowly it is considered a carbon sink. So the release of 52 million tons of fossil CO2 has been nearly replaced by the humus developed from the fodder and roots.
The growing of a 160 bushel corn crop is essentially carbon neutral. A slightly higher yield and the crop becomes a net carbon sink. Two hundred bushel corn crops are not uncommon.
The foregoing calculations are supported by NASA research and data from Michigan State University. In 2013, NASA did florescent measurements over the Corn Belt in July that indicated crops were photosynthesizing at a pace 40 present greater than the Amazon rain forest. July only, not the rest of the year. Michigan State University released calculations in 2007 that showed an acre of corn can remove 16 tons of CO2 per acre per year.
Based on their calculations, the Climate Exchange program in Michigan allows payments to farmers — who follow certain practices such as no-till — for sequestering up to 0.6 tons of CO2 equivalent per acre per year.
Jack DeWitt is a farmer-agronomist with farming experience that spans the decades since the end of horse farming to the age of GPS and precision farming. He recounts all and predicts how we can have a future world with abundant food in his book “World Food Unlimited.” A version of this article was republished from Agri-Times Northwest with permission.
