Nebraska produced 1.81 billion bushels of corn in 2019. Approximately 790 million bushels goes to ethanol production.
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 to break starches into indivual sugar molecules, 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 and thus not taxed as drinkable alcohol.
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 break the starch to simple sugars. Cellulosic feedstocks are more recalcitrant and require more time different steps break cellulose into its simple sugars.
The renewable fuel standards set by congress in 2005 and 2007 set blending requirements for blending biofuels with petroleum fuels. Demand for ethanol increased due to these blending requirements as well as demand for oxygenates and Octane boosters (Ethanol is an oxygenate as well as boosts Octane rating when blended with gasoline). Ethanol production capacity is 15.36 billion gallons in 2022 up from 10.6 billion gallons per year in 2009 (eia.gov).
Corn production in the U.S. reached record highs in 2021 with 15.1 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 42.2 billion gallons of ethanol. Compare this the US gasoline consumption in 2022 of 135 billion gallon per year (Energy Information Administration). Yet, using all of our corn for ethanol is not realistic and has not been proposed. Creating the 15.36 billion gallons under the RFS-2 would require 5.48 billion bushels or about 36% of our 2022 corn crop. Approximately 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 should be considered. When distillers are accounted for ethanol is made from 24% of our 2022 corn crop. Corn ethanol blending has shown some small increases due to expanding sales of 15% percent blends as compared to common 10% blends.
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 help 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 173 bushels per acre in 2022. 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 484 gallons per acre from 173 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 over 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 180 bushel yield goal would include: Spray, Spray, Plant, Spray, Spray, Harvest, Cart, Truck, and Dry Grain as operations for a total cost of $525 per acre if overhead (crop insurance, land, taxes, etc…) is included the total is $901 per acre. Production costs increase to over $1,100 on irrigated fields with continuous corn (Klein and McClure, 2023).
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) It is important to understand that many researchers have studied the LCA and energy balance numbers and in recent years have become interested in values beyond energy balance tending more for LCA emissions compared to gasoline. Each researcher has to establish the boundaries of their LCA, then define and defend their calculations. Because of disagreements in what to include and how to calculate things like boundaries, researchers have come to different conclusions. Readers of the research should read and understand each researchers reasons and defense of their LCA. These LCA models are quite complex and as scientists we need to be open to the ideas of other researchers while forming and defending our own reasons for which study(s) we think are most correct.
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 generations. A recognition of improvement is warrented while also noting water and air pollution still occur due to farming and improvements need to continue.
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Environmental Protection Agency - Renewable Fuel Standard Program