Soybeans germinate when the seed absorbs half its weight in water. The radical (primary root) emerges first. The hypocotyl (stem) follows soon, growing upward and pulling the cotyledons ("seed leaves") with it.
The hypocotyl extends and the cotyledons open and begin to turn green. Emergence occurs 5 to 10 days after planting, depending on field conditions. Lateral roots begin to grow and absorb water and nutrients.
The VC stage begins when the unifoliate leaves unroll (leaves no longer have edges touching). The cotyledons supply nutrients to the plant for 7 to 10 days. If both leaves are lost, yields can suffer by 8% to 9%.
After 1 set of single leaves emerges, all new emerging leaves are trifoliates - compound leaves with 3 parts or leaflets. The V stages are defined by the number of trifoliate leaves that have developed (unrolled) on the main stem, not the branches.
The V1 stage occurs with the full opening of the first trifoliate (leaf has unrolled and edges no longer touch). Every 3 to 5 days, new leaves appear through the V5 stage. Then trifoliates emerge every 2 or 3 days to the R5 stage.
At V2 (usually 6" to 8" tall), active nitrogen fixation starts. Most root nodules are within 10" of the surface. Each nodule contains millions of bacteria. Pink or red insides show active fixation. White, brown or green nodes aren't fixing enough nitrogen.
50% of the plants now have 4 opened trifoliates. Development continues at a rapid pace with branching beginning and flower buds also soon to develop depending on date and variety. Leaf feeding pests may begin colonizing.
When 5 trifoliate leaves have developed, the plant is at V5. Lateral branches may grow to compensate to some degree for low plant populations or wide row spacings. However, they can't compensate fully for underseeding.
At V5, plants reach 10" to 12". In the top stem, axillary buds develop; they'll grow into flower clusters (racemes). The total number of nodes the plant can produce is set. If something damages the growing point, the axillary buds will branch off and grow profusely.
If the plant breaks off below the cotyledon node, the plant will die. It's now about a week until flowering begins.