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Soybean Growth and Development (6/7/12)

Soybean seed, after is has absorbed water (about 50% of its seed weight) and under favorable growing conditions will start to germinate. The primary root will first emerge from the seed. As the germination process continues the stem (hypocotyl) will emerge and pull the coltyledons toward the soil surface.

The hook-shaped stem will straighten and the cotyledons will unfold. The growing point is located between the two cotyledon seed leaves (Image 1). In the axil between the cotyledons and the developing stem are two axillary buds. If the apical dominant growing point gets damaged, the axillary buds will start to develop; otherwise they tend to remain dormant. If the plant gets cut below the cotyledon leaves, there are no axillary buds and the plant will die. Soybean seedlings have a red pigment in the subepidermal layer of the young stem below the cotyledons. The pigment is called malvadin (see Images 1 and 2).

Soybean images

The dominant growing point above the cotyledons will produce two unifoliolate leaves, which are positioned 90° opposite the cotyledons. The VE stage (cotyledon stage) is when the cotyledons have been pulled through the soil surface.  The VC stage is when the unifoliolate leaves are fully expanded. During the early growth of the plant the cotyledons, rich in protein and oil, provides the young plants with nutrients. Around 70% of the cotyledon dry weight is lost due to nutrient translocation. If one or both cotyledons are damaged or lost during early development of the plant, the growth rate will be reduced. There are also two axillary buds in the axils of the unifoliolate leaves and the stem. These dormant buds will develop if, at this stage, the dominant growing point is destroyed.  Further growth of the seedling produces the formation of trifoliolate leaves. When the first trifoliate is fully emerged, opened, and expanded the plant has reached the V1 (First trifoliolate) growth stage.  The vegetative stages (V stage) are determined by the number of fully developed trifoliolates on the main stem. Trifoliolate leaves on branches are not counted towards the growth stage.

Hans Kandel

Extension Agronomist Broadleaf Crops

hans.kandel@ndsu.edu

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