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Origin and Introduction
The soybean, a native of eastern Asia, is one of the oldest crops of that area and is considered to be a vital grain crop. The soybean belongs to the family Leguminosae, subfamily Papilionideae, and the genus Glycine. Glycine is composed of two subgenera, glycine and soja. The cultivated soybean, Glycine max (L.) Merr., and its wild counterpart, Glycine soja, are now classified as species of the subgenus soja. Glycine max, Glycine soja, and most species of the subgenus glycine are diploid (2n=40). Soybean was first domesticated in China from the 11th to the 7th century B.C as understood by pictographic evidence of the ancient Chines word “shu”. The wild annual soybean Glycine soja is the ancestor of Glycine max. It has been crossed with Glycine tomentella, a wild perennial relative of the subgenus glycine. Glycine tomentella and Glycine tabacina, both perennials, overlap geographically with Glycine soja and are thought to be the closest relatives of Glycine max from the subgenus glycine. The genus of Glycine is characterized by trifoliolate leaves, flowers inserted singly at each node of the raceme, a five-toothed calyx with upper pair of teeth not well united, a glabrous corolla with long clawed petals, a keel which is shorter than the wings, and estrophilate seed. There are two types of stem growth habit and floral initiation in soybean. One type is the indeterminate stem, in which the terminal bud continues vegetative activity during most of the reproductive flowering period. The second type is the determinate stem, in which the vegetative activity of the terminal bud ceases when it becomes an inflorescence.
Soybean is one of the most important oilseed crops. Since 1970, soybean production has been at least double that of any of the other oilseed crops, such as peanut, sunflower, and rapeseed. The share of soybean in world oilseed production has increased from 32% in 1965 to over 50% in the 1980s. Soybean oil accounts for 20 to 25% of the total world fat and oil production, and 30 to 35% of the total edible vegetable oil production. Another important product of soybean is protein. Soybean meal plays a key role as a protein ingredient in feeds in the USA. Poultry feeds are the largest outlet for meal, followed by swine feeds; the two account for 78% of total usage. Soybean meal has been estimated to make up more than 90% of the oilseed meals consumed in poultry feeds. Smaller quantities of soybean meal are fed to beef and dairy cattle. Production of edible protein products is small as compared to soybean meal for seed uses. Soybean cultivars grown in the United States generally contain 20-30% oil and 39-45% protein.
Soybean requires at least 2400 Corn Heat Units in one growing season. Cultivated soybean is adapted to a wide range of latitudes, from 52N˚ to 50˚s, and to a range of seasonal durations (90 to 180 days0. The four major producers, USA, Brazil, China, and Argentina, together account for 90 to 95% of the world’s production. Canada is at northern limit of the North American soybean growth range, but soybean production there has risen sharply in recent times. Temperature is usually the limiting climatic factor in short growing season areas, such as Canada.
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