Soybean School: How uneven emergence impacts yield

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Many agronomic and environmental factors can contribute to uneven soybean emergence. From variable planting depth to moisture availability at seeding depth or untimely rains that seal some seeds underground — every uneven soybean field has a story.

Ontario Ministry of Agriculture, Food and Rural Affairs soybean specialist Horst Bohner has seen his fair share of uneven fields, but he doesn’t get too excited about variable emergence. On this episode of the RealAgriculture Soybean School, Bohner and host Bernard Tobin visit a field that features plants at the V2 stage, or 2nd trifoliate, as well as a flush of vegetative cotyledons (VC stage) that have just pushed through the soil surface.

If this were a corn field, the variability would be big trouble, but Bohner is not too worried. At this point of the season, late June, there’s a three week maturity difference between the groups of plants but soybeans can close that maturity gap as the summer progresses. “If they come up three weeks later, they’ll only be one week later in maturity in the fall… and we’ll be able to harvest everything at the same time,” he notes.

But this uneven field does present management challenges. Bohner notes that weed control is especially important in fields like these. With plants developing at different growth stages, weeds are often larger and growers need to hit them hard. In this case Bohner recommends spraying based on the growth stage of the weed rather than the soybean. (Story continues after the video.)

Bohner also addresses when a growers should consider replanting soybean fields based on emergence and plant populations. Key considerations include soil type and whether the stand, although reduced, is even across the field.

See Related: Soybean School: Replant strategies for dry soils

Bohner notes that he often sees scenarios where large parts of the field have a 110,000 plant population, but knolls have only 20,000 plants. In these cases, replanting the low population areas is warranted. In the video, he also shares University of Purdue research that indicates that replanting or “thickening” often only contributes a small portion of the the final yield in replant fields and growers need to assess when this practice makes economic sense.

What about the yield potential of late-emerging or replanted soybeans? Bohner says August growing conditions and moisture availability are two of the most important factors that determine yield. Research indicates that emergence and population problems typically reduce yield potential by five to seven bushels. “But that does not mean you can’t get 55 or 60 bushels… It could still be a terrific crop even if it’s planted the very last day of June.”

Tap here for more Soybean School videos.

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Soybean School (view all)Season 12 (2023) Episode 18
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