The cultivated soybean Glycine max L. is a member of the subgenus Soja, genus Glycine and the family Fabaceae. Soybean is not a true pulse crop. This subgenus contains only one other species, Glycine soja L. While the cultivated form, Glycine max, has never been found in the wild, Glycine soja is found throughout China and the adjacent areas of the old Soviet Union, Korea, Japan and Taiwan. Most authorities agree that domestication of soybean took place in north eastern China as early as the 11th century BC. From China, it was introduced into Korea and Japan, probably after 200 BC, and has since spread widely throughout Asia.
Europeans became aware of soybean around the late seventeenth century, and movement of the crop into the United States took place around 1800. During the 20th century, soybean was subject to major development in the U.S., resulting in the crop becoming dominant in world oilseed trade. Other countries, including Australia, Brazil and Argentina, have adopted soybean directly from the United States.
Soybean has two common growth habits.
- Begin to flower at lower nodes while terminal buds continue to grow vegetatively
- Flowering normally begins at the fourth or fifth node above the soil surface and proceeds at successive nodes above and below this node
- Terminal buds eventually turn reproductive and flower, with fruits first forming close to the base of the plants
- Indeterminate cultivars are grown in the northern U.S. and in soybean growing regions of Canada
- Produce flowers at all nodes over a short period, and each terminal bud forms a distinct raceme with a dense cluster of flowers at the top of the plant.
- Determinate cultivars are usually shorter and more branched than the indeterminate ones
- Virtually all soybean grown south of 36˚ N plus most tropical soybean are determinate
- Soybean germination is epigeal and occurs within three to four days at an air temperature of 25˚ to 30˚ C
- Rate of development is controlled primarily by photo- period and temperature. Most are short day plants, but some early maturing cultivars (adapted to extreme latitudes) and a few later maturing and tropical cultivars are day length neutral during the period from planting to flowering
- Flowering will begin within 25 to 50 days of planting, or even later (depending on cultivars and environmental conditions)
- Soybean is almost completely self-pollinated
- Pods contain from one to five ovules, but most cultivars have three ovules per pod
- Soybean is a summer-growing annual legume well adapted to moderately high temperatures
- Seedling stages are frost susceptible
- Air temperature above 20˚ C is required for optimum flowering and seed formation
- Even at ripening stage, temperatures should ideally be above 18˚ C
- Highest yields are obtained when the full growth cycle is completed under high temperatures
- Soybean is adapted to a wide range of soil types
- While neutral pH is preferred, the crop has been grown in soils ranging from pH 4.0 to 8.5
- Since high moisture availability is an important requirement for optimum yield, soil types with low moisture holding capacity can limit yield
- In more arid areas, irrigation is essential for successful soybean production. Soil types with poor water infiltration (which prevents successful irrigation) can be a limiting factor