The following descriptions of soybean growth stages are taken from the Iowa State University publication "Soybean Growth and Development " (PM 1945).
Using soybean growth stages to maximize yield
Management strategies for improving soybean yield are most effective when you are able to identify the growth stage in which potential yield is affected. For example, the effects of fertilization, frost or hail, moisture stress, plant diseases, and pesticide application on yield will be determined by the growth stage in which these events occur.
How to identify growth stages
The system of soybean growth stages divides plant development into vegetative (V) and reproductive (R) stages. The vegetative stages are numbered according to how many fully-developed trifoliate leaves are present. The reproductive (R) stages begin at flowering and include pod development, seed development, and plant maturation.
The stages can overlap. When determining the growth stage of your crop, consider that a growth stage begins when 50% or more of the plants are in or beyond that stage.
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| Vegetative Stages | ||
|---|---|---|
 |
VE |
Emergence - cotyledons have been pulled through the soil surface |
 |
VC |
Unrolled unifoliolate leaves - unfolding of the unifoliolate leaves |
 |
V1
|
First trifoliolate - one set of unfolded trifoliolate leaves |
 |
V2 |
Second trifoliolate - two sets of unfolded trifoliolate leaves |
 |
V4 |
Fourth trifoliolate - four unfolded trifoliolate leaves |
|
V(n) |
nth trifoliolate - V stages continue with the unfolding of trifoliolate leaves. The final number of trifoliolate's depends on the soybean variety and the environmental conditions |
|
|
Reproductive Stages |
||
 |
R1 |
Beginning flowering - plants have at least one flower on any node |
 |
R2 |
Full flowering - there is an open flower at one of the two uppermost nodes |
 |
R3 |
Beginning pod - pods are 3/16 inch (5 mm) at one of the four uppermost nodes |
 |
R4 |
Full pod - pods are 3/4 inch (2 cm) at one of the four uppermost nodes |
 |
R5 |
Beginning seed - seed is 1/8 inch long (3 mm) long in the pod at one of the four uppermost nodes on the main stem |
 |
R6 |
Full seed - pod containing a green seed that fills the pod capacity at one of the four uppermost nodes on the main stem |
 |
R7 |
Beginning maturity - one normal pod on the main stem has reached it's mature pod color |
 |
R8 |
Full maturity - 95% of the pods have reached their full mature color |
ISU Extension publication Soybean Growth and Development (PM 1945)