Introduction
Soybean acreage is much greater than other oilseed crops, leading to substantial soybean oil production and its availability as a biofuel feedstock.
Soybean (Glycine max) is a major crop throughout much of North America, South America, and Asia. The United States is the world’s greatest producer, producing approximately 32% of the world's soybeans, followed by Brazil with 28%.
Soybeans originated in Southeast Asia, with first domestication reported in the 11th century BC in China. First planted in the United States in 1765, soybeans spread to the Corn Belt by the mid-1800s with major acreage not seen until the 1920s, when it was used mainly as a forage crop. Major U.S. expansion as an oilseed crop began in the 1940s.
Soybeans contain approximately 18% to 20% oil compared to other oilseed crops such as canola (40%) and sunflower (43%). At 48 pounds per bushel, soybean meal remains a major product from soybeans and is used for animal feed and human food.
Current Potential for Use as a Biofuel
Soybean oil is currently a major feedstock for production of biodiesel (NBB). The most common method of biodiesel production is a reaction of vegetable oils or animal fats with methanol or ethanol in the presence of sodium hydroxide (which acts as a catalyst). The transesterification reaction yields methyl or ethyl esters (biodiesel) and a byproduct of glycerin.
Note that biodiesel is not straight vegetable oil burned in a diesel engine. Numerous studies between 1980 and 2000 have shown the use of straight vegetable oil, including soybean oil, causes carbon deposits and shortens engine life.
Biodiesel use in diesel engines does not have similar negative effects. Use of soybean oil for biodiesel was greatly influenced by promotion from U.S. soybean farmers through the United Soybean Board (USB) and subsequent creation of the National Biodiesel Board (NBB).
Biology and Adaptation
Soybean is a cool-season legume which can be grown from south to north throughout much of the eastern half of the United States. Soybeans and other legumes have a unique relationship with a bacteria bradyrhizobium species, which will colonize on soybean roots, forming a nodule. The two species form a symbiotic relationship in which the soybean plant provides nutrition and the bacteria fixes nitrogen from the air. This relationship reduces the need for supplemental nitrogen fertilizer in soybean production.
Soybeans flower in response to day length and temperature. Varieties grown in the United States are divided into 13 maturity groups, from maturity group 000, which is the earliest and adapted to northern regions of Minnesota and southern Canada, to maturity group X, adapted to southern regions such as south Texas. The earlier varieties bloom when days are long and nights are short, while the later-maturing varieties bloom under relatively shorter days and longer nights. Summer days are longer at northern latitudes, where early-maturing varieties will initiate flowering when days are longer. Maturity groups develop differently, and knowing the growth habit of different maturity groups can help with the crop management .
Production and Agronomic Information
Through much of the upper Midwest, soybeans are planted in April to June and harvested in September to November. Soybeans are well adapted to grow in soils similar to corn production. In many cases, soybeans are grown in rotation with corn or wheat to break insect, weed, and disease cycles.
Nutrient requirements are generally less for soybeans than other crops. Major nutrient requirements include nitrogen, phosphorous, and potassium. Much of the nitrogen is gained through a relationship with bacteria. A soil pH in the range of 5.5 to 7.0 will enhance nutrient availability and soybean growth.
Weed control is necessary to achieve optimal yields, and use of biotech seeds has eased the ability to control weeds during the growing season. Currently in the United States, over 90% of soybeans planted are herbicide resistant.
Many insects and diseases are common in soybeans grown in the upper Midwest. The most damaging pest to soybeans is soybean cyst nematode, a soil-borne parasitic roundworm that feeds on soybean roots . Insect pests include bean leaf beetle, soybean aphid, green clover worm, and spider mites. Soybean harvest begins after 95% leaf senescence when beans are at 12% to 18% moisture.
Potential Biofuel Yields
Current U.S. production of soybeans in 2009 was 3.4 billion bushels from 77.4 million acres. Average yield per acre for the United States was 44 bushels per acre (National Agricultural Statistics Service). One bushel of soybeans can yield 1.5 gallons of biodiesel (NBB). Using all U.S. soybeans for biodiesel could produce 5.1 billion gallons of biodiesel. However, using all soybean production for biodiesel has not been proposed and is not realistic.
In 2009, biodiesel production was 700 million gallons with a production capacity of 1.83 billion gallons . Based on a yield of 44 bushels per acre, an acre of soybeans could yield 66 gallons of biodiesel, compared to 69 gallons for a 1,300-lb per acre canola yield, 84 gallons for sunflower and over 600 gallons for palm oil .
Production Challenges
Soybean production generally complements corn production in the upper Midwest. Both corn and soybeans enjoy a long history of production on millions of acres in the upper Midwest. This history has led to a large infrastructure of equipment, storage, rail, barge, and truck transportation.
Soybeans, like many crops, face insect and disease pests along with weather-related challenges. An emerging disease has gained much attention in recent years. Soybean rust, a fungal disease native to Asia, has spread to the soybean fields of South America and finally to U.S. soybeans. Rust control is expensive, requiring fungicide applications, and yield damage can be extreme.
Estimated Production Costs
Production costs will vary depending on location, cropping systems, and fluctuation in price of energy. Major expenditures in soybean production include planting, harvesting, seed, and pesticides. An example of a Nebraska rain-fed budget for no-till soybeans for 2010 lists $115 per acre for field operations, materials, and services. When including overhead costs for land, insurance, etc., the total is approximately $200 per acre. Total costs for irrigated soybeans are around $400 per acre.
Biodiesel profitability is extremely variable and based on the continuously changing prices of biodiesel, soybean oil, co-product glycerin, methanol, and natural gas. Price of soybean oil feedstock is one of the driving factors in profitability .
Environmental and Sustainability Issues
The capacity of soybeans used for biodiesel production grew from zero to over a billion gallons per year in the past two decades (1990s and 2000s). During that time, biodiesel production rose and fell depending on the price of feedstock, price of petroleum oil, and federal and state subsidies provided to the industry.
One major challenge for soybeans is the competing uses for soybean oil. Soybean oil is used in human food products, as cooking oil, and for numerous industrial applications. Soybeans account for 80% or more of the edible fats and oils consumed in the United States . Competition with other uses has caused price spikes in the soybean oil market, challenging the profitability of soybean biodiesel .
A 2009 life cycle analysis of biodiesel done by the USDA found that soy biodiesel yields 4.56 times the fossil energy needed to produce it. In comparison, petroleum diesel has a fossil energy ration of 0.84 .
