Soybean

Soybean

Soybean, Glycine max, is an important crop throughout the world. Soybean is a source of food, oils—both culinary and industrial—and animal feed. In addition, soybean products can be found in plywood, particleboard, printing inks, soap, candy, cosmetics, and antibiotics.

Cultivated soybean and its wild ancestor, Glycine soja, are members of the legume family, Fabaceae. Legumes are particularly valuable because, in conjunction with symbiotic bacteria, they fix atmospheric nitrogen and they are excellent sources of protein, with soybeans containing the highest level of this nutrient.

The cultivated soybean plant is an erect, bushy annual. Plants produce clusters of three to fifteen purple or white flowers that develop into pubes-cent (fuzzy) pods, usually containing two to four seeds. Soybean seeds vary in size and are commonly yellow in color, but can also be green, black, or brown. Soybean varieties are classed into thirteen maturity groups according to their response to day length; the earliest group, 000, developed for far northern latitudes and the latest group, X, for tropical regions. Groups 000 through IX are grown across the central and eastern United States from Minnesota and North Dakota in the north to Florida and southern Texas in the south.

The soybean originated as a cultivated crop in northeast Asia about four thousand years ago. The earliest written record of the soybean plant is from China in 2838 B.C.E. Early farmers grew soy for their own food as well as for livestock feed. Soybean came to the United States in the late 1700s, but was used primarily as a forage crop until the beginning of the twentieth century.

Soybean is planted in the spring with row spacing averaging twelve inches using a grain drill. A skipped row system allows cultivation without damage from tractor tires. Nitrogen fixation by the symbiotic Rhizobium bacteria alleviates the need for nitrogen fertilizer, although soil testing may indicate other needed nutrients. Weed and insect pest controls are practiced as needed. Soybean is harvested when the pods are dry and brown and the leaves have fallen, generally after the first freeze in the fall. The crop is harvested with combines that cut the plants and thresh the seed from the pods.

More soybeans are grown in the United States than in any other country in the world. Soybean is the second largest crop produced in the United States after corn. Over half of the soybeans produced in this country are exported to other parts of the world, making soybean an important part of the market economy of the United States.

Greater than half of the vegetable oil consumed in the United States is soy oil, a healthy vegetable oil high in unsaturated fats. Culinary soybean products include extracted soy protein, tofu (soybean curd), tempeh (fermented soybean mash), soy sauce, soy flour, edamame (green vegetable soybeans), soy sprouts, and soymilk. Other important soybean products are the animal feeds made from the meal that is one of the end products of oil extraction, and oil for light industrial purposes.

see also Agriculture, Modern; Economic Importance of Plants; Fabaceae; Nitrogen Fixation.

Molly M. Welsh

Bibliography

Poehlman, John Milton. "Breeding Soybeans." In Breeding Field Crops. New York: Van Nostrand Reinhold, 1987.

A Short History of Soybeans. 1999. [Online] Available at http://www.cyberspaceag.com/soybeanhistory.html.

"Soybean Production." In Ohio Agronomy Guide Bulletin 472. 1999. [Online] Available at http://www.ag.ohio-state.edu/~ohioline/b472/soy.html.

Whigham, Keith. Soybean History. Department of Agronomy, Iowa State University. 1999. [Online] Available at http://www.agron.iastate.edu/soybean/history.html.