Each spring, Mother Nature has a tendency to impact the planting schedule and stand establishment of our soybean crop. One of the toughest early season questions may involve plant stand evaluations. How well did the variety establish a uniform stand? Early in the season, various hurdles are placed in front of the soybean seed from germination and emergence to a final, uniform stand. Some of the “hurdles” that can impede a uniform soybean stand include inaccurate planter adjustments, planting speed, soil crusting and moisture extremes, weather patterns, disease threats, pests, seed quality and seed treatment management.
As cited in Iowa State’s Extension publication (Soybean Replant Decisions–PM1851), in most situations, stand reduction occurs in 2 forms: lack of uniformity across the field or gaps within the row. Stand reductions are typically patchy in distribution across a given field. Examples of non-uniform stand reductions may include drowned-out areas, sandy, well-drained spots with inadequate amounts of soil moisture, high traffic compacted soils or pest-infested areas. Gaps less than 2 feet in diameter will be compensated by adjacent or surrounding soybean plants. Gaps greater than 2 feet in diameter usually contribute to reduced yields.
Reasons for skips:- Larger seed for the cup (disc) to hold
- Faster planting speeds (seed bouncing)
- Faster planting speeds plus higher seeding rates (lots of bouncing)
Reasons for doubles:- Larger cup (disc) oversized, allowing more beans to be planted
- Increase in vacuum pressure
Table 1. Percentage of full-yield soybean potential, as influenced by plant density established and stand reduction 2 to 4 weeks after planting.
Table 2. Effect of plant density at 3 stages of soybean yield development.
Estimating Plant StandsTo effectively diagnose and provide guidance, knowing how to evaluate and estimate plant stands is a significant first step. Refer to Tables 3 and 4 to accurately assess plant stand.
Table 3. Plant Density for Common Row Widths (based on number of plants per feet of row)
Table 4. Plant Density per Square Yard or “Hula Hoop Method” (hoop diameter = inches)
Replant once you’ve determined the following:
- Validated the cause of the stand loss
- Stand assessment
- Uniformity
- Gaps
- Remaining stand
- Yield potential of remaining stand
If you have answers to all 3 points, you can make an informed decision on keeping or replanting the stand, but keep in mind the following factors:
- Original and new re-planting date
- If the existing stand is between 73,000 and 90,000 plants per acre, the stand is uniform and it is early June or later, university data suggests keeping the stand
- Planting soybean seed to fill in the stand is not recommended
Table 5. Relationship of Plant Population and Planting Date on Soybean Yield Potential
Contact your
Golden Harvest Seed Advisor with questions or for additional agronomic insights.
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