The parts of a soybean plant develop in specific ordered stages in which each part plays a key role in the plant's growth development, without which the plant cannot grow and produce a healthy crop. According to the University of Minnesota Extension, the timing of soybean flowering and maturity depends on climate and light conditions in the planting location. Observing the plant parts as they emerge can give growers a better idea of where the soybeans are in their development cycle and indicate when they will be ready to harvest.
Soybean seeds have two halves, called cotyledons, which store protein, oil and carbohydrate nutrients for the developing seedling as it germinates. When moisture activates the germination process, enzymes are released to digest the stored food and carry it to the other parts of the plant embryo. The cotyledons provide nourishment to the young plant until leaf development reaches the point when the leaves can manufacture sufficient energy through photosynthesis to sustain the soybean plant.
The first pair of primary leaves grow opposite one another just above the cotyledons. Subsequent leaves grow in three parts along the stem, on alternating sides at the nodes. The University of Minnesota Extension explains, "A primary function of leaf tissue is to intercept light (solar energy) and convert it into food (chemical energy). This food is used by the young plant to develop roots, stems and more leaves." The axillary leaf buds are where the petiole or leaf stem attaches to the plant's main stem.
At the top of the soybean stalk there is a terminal growing point where a cluster of rapidly dividing cells forms new leaves. Most new growth springs from this point unless it is damaged or destroyed. If that happens, the axillary buds may sprout branches, flowers or soybean pods.
Soybean plant flowering depends on available daylight and temperatures. The National Soybean Research Laboratory advises that while soybeans require a soil temperature of 55 degrees Fahrenheit or more to germinate, they are a heat-loving plant requiring full sun to thrive. The sooner they get the required sunlight and warmth, the sooner they will flower. The small white, pink or purple flowers grow in bud clusters of three to fifteen at the nodes and are self-pollinating.
The NSRL indicates that 50 to 80 percent of the flower buds will grow soybean pods. The first generally appear seven to 14 days after flowering but take three to five months to mature. The outer pod shell is not edible, so the soybeans need to be shelled to get at the edible beans inside, which look like oval green peas. Each pod produces two to four soybeans.