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bioweb.sungrant.org » Technical » Biomass Resources » Agricultural Resources » Existing Crops » Corn
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Corn (Zea mays) production in the U.S. includes both corn produced for silage (corn which is harvested wet and fed to livestock much like hay and forage crops) and corn produced for the grain. The majority of production is for corn grain (about 92% of total harvested acres). On average, around 71 million acres of corn are harvested for grain annually although acres vary by year. Average national grain yields have ranged from 129 to 160 bushels/acre between 2000 and 2006, mostly due to weather (table 1). Production is concentrated in the Midwest (about 80% in the states of Illinois, Indiana, Iowa, Kansas, Minnesota, Missouri, Nebraska, South Dakota, Ohio, and Wisconsin), but occurs in nearly every state except New England (USDA-NASS) (figure 1). Currently, about 80% of corn is produced in rotation with another crop, typically soybeans (75%), although other crops (e.g., wheat, rye, barley, and oats) are also used (Kim, 2003; USDA-ERS, 2006). Corn tillage practices vary substantially by region—at a national level, 62% of corn acres used conventional till operations, 18% used reduced till operations, and 20% employed no-till methods in 2004 (Conservation Technology Information Center, 2004).
Corn is typically planted in 30 to 38 inch wide rows at a rate that yields 28,000 to 32,000 plants/acre. In the Midwest, it is typically planted between mid-April and early May (when soil is about 50°F at the planting depth of 2 inches) (ISU, 2001). In 2005, about 96 % of all planted corn acres received nitrogen fertilization at a national average rate of 138 lbs N/acre, but ranging from 67 to 171 lbs N/acre depending on state. For the five largest corn producing states (IA, IL, IN, MN, and NE), state average nitrogen application rates range from 138 to 147 lb N/acre. The national average phosphorus application rate is 58 lb P2O5/acre (range of 35 to 77 lb/ac) and 81% of all planted corn acres received phosphorus applications in 2005. The national average potassium application rate is 84 lb K2O/acre (range of 19 to 124 lb/acre) applied to 65% of all planted corn acres in 2005 (USDA ERS). Pounds of active ingredients of pesticides (i.e., insecticides, herbicides) applied to corn acres decreased from 227.3 million lbs active ingredient in 1997 to 174.6 million lbs active ingredient in 2004. The decline is due to changes in management, use of newer herbicides that are applied at lower rates, and the adoption of genetically modified corn varieties for weed and insect control. In 2005, about 25% of U.S. corn acres were planted with herbicide tolerant corn varieties and 35% of corn acres were planted to bt corn varieties (corn varieties that contain bacillus thuringensis to control root cutworms) (Fernandez-Cornejo, 2006).
The costs of producing corn vary widely. In 2001, production costs ranged from an average $1.08/bushel for the 25% of producers with the lowest costs to an average of $2.98/bushel for the 25% of producers with the highest costs. Low cost producers generally have larger farms and more corn acres, have higher yields/acre, are less likely to irrigate, and more frequently utilize reduced tillage and crop rotations than do high cost producers (Foreman, 2006).
The majority of corn produced in the U.S. is used as livestock feed. About 15% of the corn is exported and around 7% is used to produce sweeteners (e.g., high fructose corn syrup used in soft drinks). A significant and increasing portion of corn production is currently used to produce bioenergy and bioproducts. In 2005, about 2.15 billion bushels of corn (of the 11.11 billion bushels produced) were used to produce 3.9 billion gallons of fuel ethanol (USDA-ERS; RFA, 2006). Corn is also being used to produce bioproducts, such as polylactic acid (biodegradable plastic) and 1,3-propanediol (used to produce Sorona®, a synthetic fabric). Additionally, corn stover (the above ground, non-grain portion of the corn plant) could be collected and used as a bioenergy and bioproduct feedstock. About 1 dry ton of corn stover is produced for every 1 ton of corn grain. After leaving sufficient quantities of stover on the field to maintain the health and productivity of the soil, several million dry tons of corn stover could potentially be available as a biomass feedstock.
Corn production has steadily increased over time. Since 1966, corn production has increased from 4.17 to 11.11 billion bushels. About 20% of the increase is due to increased acres with the remainder due to increased yields resulting from genetic improvements and changes in management (figure 2). Yield increases have averaged 1.8 bushels/ac/yr between 1965 and 2005 (CAST, 2006).
Corn yields are expected to continue to increase in the coming years. A workshop of crop and livestock experts (English, 1997) projected that under the mostly likely scenario, average national corn grain yields of 215 bu/ac and 260 bu/ac could be achieved by 2030 and 2050 respectively (compared to the 1990-1992 yields of 120 bushels/acre) resulting from combined genetic, management and equipment improvements. The USDA projects average national yields of 163.9 bushels/acres and 77.2 million harvested acres by 2015 (USDA OCE). FAPRI projects average national corn grain yields of 164 bu/ac and 78.7 million harvested acres by 2015 (FAPRI, 2006). Industry sources indicate the potential of substantially higher grain yields. The increased yields are expected as a result of improved moisture and nutrient use, cold tolerance, and resistance to pests, diseases, and weeds. Seed producers are incorporating multiple characteristics (stacking) into the new varieties under development (Pioneer, 2007; Fraley, 2006; Syngenta, 2007).
In addition to increasing grain yields, research is ongoing to develop new varieties with traits more conducive to the use of corn for bioenergy and bioproducts. Approaches include modifying the corn to have new or improved functions, more uniform functions, or decreased processing costs. Examples include improving the starch content and/or the fermentation efficiency (i.e., the amount of total starch broken down into glucose) such as waxy corn (which contains higher proportions of amylopectin--starch made up of branched chains of glucose molecules); high amylose corn (amylose is starch composed of linear chains of glucose molecules) (Johnson, 1999; Pioneer, 2007); highly extractable starch corn that yields about 2% more extractable starch than commodity corn varieties in wet milling applications (University of Illinois, 2003; Pioneer, 2007); and high total fermentable hybrids that provide a increase in ethanol yields per bushel of corn (about 2-4%) in dry mill applications (Fraley, 2006; Pioneer, 2007). Modifications to the starch are also being explored such as introducing functional groups (such as aldehyde groups) or lengthening the starch chains (Johnson, 1999). Other approaches include development of corn varieties containing amylase enzymes (enzymes that break down the corn starch into sugars). Use of these varieties could reduce the amount of amylase enzymes that would need to be added in the conversion process (BBI, 2006b; Syngenta, 2007). |
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Bryan and Bryan International, The search for a perfect ethanol corn, Ethanol Producer Magazine, 2006a,
www.ethanolproducer.com/article-print.jsp?article_id=1619
Bryan and Bryan International, Syngenta to offer U.S. amylase corn in 2007, Ethanol Producer Magazine, 2006b,
www.ethanolproducer.com/article.jsp?article_id=2113&q=&category_id=3.
Council for Agricultural Science and Technology (CAST), Convergence of Agriculture and Energy: Implications for Research and Policy, CAST Commentary QTA 2006-3, CAST, Ames, Iowa, November 2006.
English, B.C., R.L. White, and L. Chuang, Crop and Livestock Technologies, RCA III Symposium, Iowa State University Press, Ames, IA, 1997.
Food and Agricultural Policy Research Institute (FAPRI) (January 2006), FAPRI 2006 U.S. and world agricultural outlook, Iowa State University and the University of Missouri-Columbia, FAPRI Staff Report 06-FSR 1.
Fernancez-Cornejo, Jorge and Margriet Caswell, The first decade of genetically engineered crops in the United States, U.S. Department of Agriculture, Economic Research Bulletin, Economic Information Bulletin No. 11, April 2006.
Foreman, Linda, Characteristics and production costs of U.S. Corn Farms, 2001, U.S. Department of Agriculture, Economic Research Service, Economic Information Bulletin Number 7, February, 2006.
Fraley, Robb, Chief Technology Officer, Monsanto Corporation, Presentation to the Citigroup “Ethanol on the Cob” Conference, October 3, 2006.
Iowa State University, University Extension, Corn Planting Guide, PM 1885, September 2001.
Johnson, Lawrence A., C. Phillip Baumel, Connie L. Hardy, and Pamela J. White, Identifying valuable corn quality trains for starch production, Iowa State University, Center for Crops Utilization Research, EDC 194, November 1999.
Pioneer Seed Company, Industry Select Seed Varieties, www.pioneer.com.
Renewable Fuels Association, www.ethanolrfa.org.
Syngenta Corporation, 2007, www.syngentacropprotection-us.com.
University of Illinois, High Extractable Starch Corn—Updated 2003, http://web.aces.uiuc.edu/value/factsheets/corn/fact-highstarch-corn.html.
U.S. Department of Agriculture, Office of the Chief Economist, USDA agricultural baseline projects to 2015, Baseline Report OCE-2006-1, February 2006.
U.S. Department of Agriculture, Economic Research Service, Data Sets, U.S. Fertilizer Use and Price, www.ers.usda.gov.
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