Soybean Growth Stage Influence on Crop Management Decisions

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Accurately identifying soybean growth stages can help growers anticipate the effects of frost, hail, moisture stress, diseases, insects, and weeds on soybean yield potential. Growth stages may also guide you to make timely management decisions, such as when to apply a fungicide or an insecticide. Vegetative (V) growth stages are numbered according to the number of fully developed trifoliate leaves present. Reproductive (R) stages begin at flowering and progress through pod development, seed development, and plant maturity. Vegetative growth stages begin to overlap reproductive stages at about R1. Minimizing stresses during vegetative, and particularly reproductive stages, can help soybeans achieve full yield potential. A new growth stage is established when 50% or more of the plants meet the requirements of the growth stage (Figure 1).

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Figure 1. Soybeans are either indeterminate or determinate in growth habit. Indeterminate soybean vegetative growth continues after flowering . Determinate soybeans have generally completed vertical growth by the time flowering is completed. Source. University of Illinois. 1999.13;10;13;10;13;10;

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Figure 2. Early-season soybean plant.13;10;13;10;

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  • Emergence (VE) to Cotyledon (VC): Over 5-10 days the radical (primary root) emerges, followed by the hypocotyl (stem), which pulls the cotyledons (seed leaves) to the soil surface. The first two unifoliate leaves emerge. This process can be stimulated by small amounts of fertilizer placed in a band to the side and slightly below the seed; however, doing this may delay colonization of rhizobia on the root system, delay nodulation, and potentially reduce the amount of nitrogen (N) produced by the plants. XtendiMax® Herbicide with VaporGrip® Technology may be applied from cracking up to and including beginning bloom (R1) in Roundup Ready 2 Xtend® soybeans.
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  • Cotyledon (VC) to First Trifoliate (V1): Loss of both cotyledons soon after the VE stage may reduce yield potential by 8-9%. The first trifoliate (Figure 2) emerges and opens at V1. As each additional trifoliate emerges on the main stem, a new V stage is established.
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  • Second Node (V2): Active Nfixation begins. Plant leaves may turn yellow as plants switch from using soil-available N to fixed N. Adding N at this stage will inhibit N production by nodules. Since lateral roots are developing rapidly in the top 6 inches of soil, cultivation should be shallow to minimize root pruning.
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  • Third to Fifth Nodes (V3-V5): The total number of nodes the plant can produce is established at V5.
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  • Beginning Bloom (R1) to Beginning Pod (R3): Flowering begins on the third to sixth node. Once an open flower develops, at one of the top two nodes of the main stem, the plant is in the R2 stage. Heat or moisture stress at R3 can reduce pod numbers, bean number per pod, or seed size, which may reduce yield potential. Fungicide applications may begin as early as R2.5. Fungicide applications made prior to the R1 growth stage or after the R6 (full seed) growth stage are often not economical.1
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  • Full Pod (R4): Stress during this period can cause more reduction in yield potential than at any other growth stage.
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  • Beginning Seed to Full Maturity (R5-R8): Plants attain maximum height, node number, and leaf area. Stress during the R5 growth stage can reduce pod numbers, beans per pod, seed size, and yield potential. Seed dry matter begins to peak at growth stage R7. Full maturity occurs at growth stage R8, when 95% of pods have reached their mature color. Typically, 5-10 days of good drying conditions after R8 will be needed to reach a harvest moisture content of less than 15%.
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