Accurate identification of soybean growth stages is important to maximize grain yield and profitability because most management decisions are based upon the growth stage of soybean plants within the fields.
Two plant growth habits exist for soybean: indeterminate and determinate. Indeterminate cultivars can produce vegetative and reproductive growth simultaneously until about the R5 growth stage. Most indeterminate cultivars are maturity groups 00-IV.
In contrast, determinate cultivars will complete most of their vegetative growth prior to initiating reproduction. Most determinate cultivars are maturity groups V-IX. Soybean growth stages are divided into vegetative (V) and reproductive (R).
When identifying the vegetative growth stages of soybean, the primary consideration is the number of fully developed leaves on the main stem. A fully developed leaf has all leaflets open, while an undeveloped leaf has leaflet edges that are still touching.
Reproductive growth stages are identified by specific flower, pod, and seed characteristics. When classifying a soybean field as a specific growth stage, at least 50% of the plants in the field must be at or beyond that growth stage.
Emergence (VE) can occur from late April through June. In this stage, the cotyledons and growing point are above the soil surface. Cotyledon (VC) occurs May through June/July.
Two unifoliate leaves are fully developed and nitrogen-fixing root nodules may be visible, but not functional. V1 occurs May through June/July. At this stage, one trifoliate leaf is fully developed and N-fixing root nodules are still not functional. V2 occurs May/June through June/July.
At this stage, two trifoliate leaves are fully developed and N-fixing root nodules are working. V3 occurs June through July. During this stage, three trifoliate leaves are fully developed.
It typically occurs two to three weeks after emergence for full-season soybean and two weeks after emergence for double-crop soybean. This is the final growth stage when several herbicides can be applied.
V4 and on occurs June through July.
In these stages, four and more trifoliate leaves are developed. The number of trifoliate leaves is determined by variety maturity and environmental conditions.
R1 can occur from late June through August. At this stage, flowering begins.
One flower at any node on the main stem is open. Environmental stress or plant injury typically has minimal effect on yield.
During R2 (full flowering), a flower on the main stem opens at one of the two top nodes with a fully developed trifoliate leaf. Rapid growth and nutrient accumulation in vegetative plant parts begin.
Environmental stress or plant injury typically has minimal effect on yield. In the R3 stage, pods begin. A 3/16-inch long pod is on the main stem at one of the four top nodes with a fully developed trifoliate leaf. Environmental stress or plant injury typically has minimal effect on yield.
This is usually when the last pesticide applications occur. R4 (Full Pod) occurs early/mid-August. At this stage, a 3/4-inch long pod is on the main stem at one of the four top nodes of a fully developed trifoliate leaf. Beginning with this growth stage, yield can be greatly reduced due to environmental stress and/or plant injury. R5 occurs mid/late August.
In this stage, a 1/8-inch long pod is on the main stem at one of the four top nodes that have a fully developed trifoliate leaf. This begins a period of rapid seed growth and fill. Plant stress typically results in aborted seeds.
Environmental stress and/or plant injury can result in significant yield reductions. R6 occurs in early September. Green seed fills the pod cavity at one of the four top nodes on the main stem with a fully developed trifoliate leaf. Plant stress at this stage typically results in pod and seed abortion, which can significantly reduce yields.
At the R7 stage, one normal pod on the main stem is mature and has turned brown or tan. Soybean seed has essentially reached physiological maturity, which means the seed has attained maximum dry weight.
Rapid leaf yellowing begins. Stress that occurs at this stage has essentially no effect on yield. At the R8 stage, 95% of pods have matured and turned brown.
Stressful conditions at this stage do not affect yield unless hail or other factors remove pods from the stem.
Clint Hardy is the agricultural extension agent for the Daviess County Extension Office. He can be reached at 270-685-8480.