Nebraska produced 1.81 billion bushels of corn in 2019. Approximately 790 million bushels goes to ethanol production. Photo courtesy of F. John Hay
Corn Grain as an Ethanol Feedstock
Corn (Zea Mays) is a popular feedstock for ethanol production in the United States due to its abundance and relative ease of conversion to ethyl alcohol (ethanol). Corn and other high starch grains have been converted into ethanol for thousands of years, yet only in the past century has its use as fuel greatly expanded. Conversion includes grinding, cooking with enzymes, fermentation with yeast, distillation to remove water. For fuel ethanol two more steps are included; molecular sieve to remove the last of the water and denaturing to make the ethanol undrinkable.
Current Potential for Use as a Biofuel
Corn grain makes a good biofuel feedstock due to its starch content and relative easy conversion to ethanol. Infrastructure to plant, harvest and store corn in mass quantities benefits the corn ethanol industry. Unlike sugarcane where squeezed sugar water can be directly fermented, corn starch must be cooked with alpha and gluco-amylase enzymes to convert the starch to simple sugars. Cellulosic feedstocks are even more recalcitrant and require time and energy to convert to simple sugars.
Under the renewable fuel standard set by congress in 2007 (RFS-2) grain based ethanol can make up 15 billion gallons of the 36 billion gallon per year. Ethanol production capacity is 14.7 billion gallons in 2015 up from 10.6 billion gallons per year in 2009 (eia.gov).
Corn production in the U.S. reached record highs in 2014 with 14.2 billion bushels (National Ag Statistics Service). Using a corn to ethanol conversion of 2.8 gallons of ethanol from a bushel of corn total U.S. production of corn could produce approximately 38 billion gallons of ethanol which would provide approximately 26% of our 137 billion gallon per year gasoline consumption (Energy Information Administration). Using all of our corn for ethanol is not realistic and has not been proposed. Creating the 15 billion gallons under the RFS-2 would require 5.4 billion bushels or about 39% of our 2015 corn crop. One third of corn entering an ethanol biorefinery will leave as distillers grains which can be used to replace corn in cattle, swine, and poultry diets. This replacement of corn with distillers grains would change the numbers. It would require 27% of our 2015 corn crop. With a steady increase in yields the U.S. has the potential to increase corn ethanol production without expanding to new acres.
Biology and Adaptation
Corn (Zea Mays) originated in Central America with first domestication purported to be in the Tehuacan Valley of Mexico. Spreading throughout the North American continent corn became an important crop for early Americans. At its peak in 1917, 111 million acres of corn were planted in the U.S. Today corn is planted in many parts of the world and across many states in the U.S. from Southern North Dakota to Texas and East to New York. Corn is well adapted to growing in temperatures between 50 and 86 degrees Fahrenheit (Hoeft et. al. 2000). To produce grain, corn will use approximately 22 inches of water which requires 12 to 20 inches of rainfall or irrigation during the growing season. Many parts of the upper Midwest are well suited to grow corn and this area is sometimes referred to as the corn-belt.
Production and Agronomic Information
Corn in the upper Midwest is seeded between March and May and harvested between September and November in most years. A majority of corn planted today has genetic resistance to herbicides and some insects these traits aids producers in control of weeds and insects. In seed resistance genetics are a result of genetic engineering and plant breeding. Much of the corn-belt rotates corn production with soybeans or wheat. These rotations break weed and insect cycles and reduce the cost of production. Corn responds best to highly fertile soils with supplemental fertilizer applied in most years. Fertilizer may be inorganic chemical fertilizer or manure. Major nutrients required by corn are nitrogen, phosphorus, and potassium. Inorganic nitrogen fertilizer production is very energy intensive and as a result nitrogen fertilizer represents nearly 30% of the energy inputs in corn production (BESS 2009). Other major inputs include irrigation and grain drying. Smaller but still significant energy input to corn production are diesel fuel for tractors, transportation, harvest, and pest management chemicals and application.
Average corn yield nationally was 167.5 bushels per acre in 2015. Corn yield has increased by approximately 2 bushels per acre per year since 1940 (NASS 2009). This increase will likely continue into the future with some people predicting the yield trend to increase at a greater rate due to biotechnology and advances in breeding. Ethanol yield per acre would be 462 gallons per acre from 165 bushels of corn. An acre of sugar cane can produce approximate 35 ton yield or about 560 gallons of ethanol (Hofstrand, 2009).
Corn production is blessed with nearly 100 years of infrastructure build-up and research. Producers have great knowledge and experience growing corn. This infrastructure and grower knowledge makes corn a natural crop for expanded uses such as ethanol. Yet, high production costs and high inputs make corn a very intensive crop. Other bioenergy crops may be less intensive requiring fewer inputs. The costs versus profit per acre need to be compared as economics are a major driver in decision as to which crop is best. Growing another crop on an acre where corn could be grown has risk known as opportunity costs. Risks may include; a new cropping system, no harvest, transport, or storage infrastructure and also no commodity market to fall back upon if the biofuel market fails.
Estimated Production Costs
Production costs vary widely depending on tillage, irrigation, yield goal (soil fertility), spraying schedule or seed selection, and rotation. An example corn budget with rainfed, no-till, biotech seed, corn soybean rotation, and 125 bushel yield goal would include: Spray, Plant, Spray, Spray, Spray, Harvest, Cart, Truck, and Dry Grain as operations for a total cost of $211 per acre if overhead (crop insurance, land, taxes, etc…) is included the total is $483 per acre. Production costs increase to over $900 on irrigated fields with continuous corn (Klein and Wilson, 2015).
Environmental and Sustainability Issues
Life cycle analysis (LCA) of ethanol production from corn grain has yielded a net energy ratio of 1.2 to 1.45 (Liska et. al. 2009). This represents just a 20 to 45% positive energy balance when producing ethanol from corn. This number has been the criticism of corn ethanol because of the large amount of fossil energy used to produce ethanol. A USDA Study published in 2016 reports increased efficiency at ethanol facilities have led to fossil energy ratios nationally at 2.0 to 1 and with some individual facilities with ratios as high as 4.0 to 1. (2015 Energy Balance For The Corn Ethanol Industry)
Corn production is highly intensive row crop production including use of large amounts of fertilizer and pesticides. Over many years some water bodies have become contaminated with soil, nutrient, and pesticide runoff from agricultural fields. The increase in no-till and reduced tillage practices has reduced soil erosion and subsequently nutrient and pesticide runoff and the trend for better conservation on these acres continues. Today’s corn producers are producing more grain on less acres using better conservation techniques than the previous generation.
Biofuel Energy Systems Simulator (BESS), 2008, ver.2008.3.1, A Model for Life-Cycle Energy & Emissions Analysis of Corn-Ethanol Biofuel Production Systems, University of Nebraska-Lincoln
Bromberg L. and Cohn D.R., 2008, Effective Octane and Efficiency Advantages of Direct Injection Alcohol Engines, MIT Laboratory for Energy and Environment Report, LFEE 2008-01 RP
Environmental Protection Agency, http://www.EPA.gov
Hoeft R.G., Nafziger E.D., Johnson R.R., 2000, Aldrich S.R. Modern Corn and Soybean Production, MCSP Publications Champaign IL
Hofstrand D., 2009, Brazil’s Ethanol Industry, Ag Decision Maker, Iowa State University, http://www.extension.iastate.edu/agdm
Klein R.N., and Wilson R.K., 2010, Crop Budgets Nebraska 2010, University of Nebraska – Lincoln Extension, EC 872, January
Liska A.J., Yang H.S., Bremer V.R., Klopfenstein T.J., Walters D.T., Erickson G.E., Cassman K.G., 2009, Improvements in Life Cycle Energy Efficiency and Greenhouse Gas Emissions of Corn-Ethanol, Journal of Industrial Ecology, 13, 58-74
National Agriculture Statistics Service (NASS), http://www.nass.usda.gov
Renewable Fuel Association, http://www.ethanolrfa.org
Smith J.L. and Workman J.P., 2004, Alcohol for Motor Fuels, Farm and Ranch Series Equipment no. 5.010,
Nebraska Deptartment of Environmental Quality - look for updated maps of ethanol plants in Nebraska
Environmental Protection Agency - Renewable Fuel Standard Program