Louisiana Soybeans: Let’s Talk Growth Habits

    On June 5, I recorded a video for a virtual field day at the Dean Lee Research Center. The main topic was the current development of a planting date trial. In the trial, I have maturity groups (MG) ranging from MG 3.6 to MG 5.4. For the field day, I focused on the development of a MG 4.5, 5.2, and 5.4 variety.

    The trial is designed to have six planting dates, ranging from March 19 to June 15. On June 5, five planting dates had been sown and the first three planting dates had varieties with growth stages ranging from vegetative (no reproductive structures) to beginning seed (R5 growth stage).

    Figure 1 shows how many days from planting each MG by planting date began blooming (R1 growth stage), the vegetative stage of the variety at R1, and the current growth stage (as of June 5).

    One thing I emphasized during the recording was the difference in growth and development between an indeterminate and semi-determinate variety. A soybean plant will be categorized as one of three growth habits: indeterminate, semi-determinate, and determinate.

    Indeterminate plants will begin flowering at an early vegetative stage and will continue increasing in the number of nodes on the main stem, while simultaneously producing reproductive structures.

    Determinate varieties will mostly cease vegetative growth at the onset of flowering, and semi-determinate plants will fall in the middle with a small increase of vegetative growth after the R1 growth stage.

    Figure 1 shows there were 35-39 days between planting and R1 for two indeterminate varieties (MG 4.5 and 5.2); and there were 58 days between planting and R1 for a semi-determinate variety (MG 5.4). In addition, the 4.5 and 5.2 varieties were between the V5-V6 growth stage at R1, where the MG 5.4 variety was between the V10-V11 growth stage.

    Figure 1. Comparison of the growth and development of soybean plants of three different maturity groups and three planting dates. Click Image to Enlarge

    Deer Damage

    Last week, I reported damage from deer was one of the factors contributing to poor ratings in soybean fields. I have seen signs of deer grazing on young soybean plants from St. Mary to Madison parish. I was asked how much yield loss should be expected from deer grazing.

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    After a brief literature review, I can suggest the effect of deer grazing could decrease yield up to 74% or more. However, there are also reports of no decrease in yield after deer grazing.

    If the grazing is minimum, the soybean plant should be able to compensate. An article in the Volume 10, Issue 3 – April 2020 of the LA Crops Newsletter, “Considerations for replanting soybean,” explains that the growing point in soybean plants is above the two cotyledons.

    On top of the main stem, there is a growing point called the apical meristem. Normally, the apical meristem directly influences the architecture of the plant by controlling the growth habit. With the original apical meristem intact, the soybean plant will grow predominantly upward by the main stem increasing in height.

    If the apical meristem is cut, soybean plants have axillary buds along the main stem. These axillary buds may remain dormant or can produce axillary branches capable of producing trifoliolate leaves and reproductive structures. Of course, that is if the deer do not continue to feed on the new growth.




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