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Emergence Uniformity in Corn (06/07/18)

Now is a good time to evaluate the uniformity in emergence of the corn crop.

Emergence Uniformity in Corn

Now is a good time to evaluate the uniformity in emergence of the corn crop. Uniformity in emergence in corn is important as corn seedlings do not compete well with other plants, including other corn plants. Corn seedlings that emerge more than a week later than neighboring seedlings will not “catch up” and will yield much less than if they emerged at the same time. In extreme cases, they will not produce a cob and will act as an expensive weed. Additionally, corn does not compensate as well as many other crops when there are gaps in the row. The optimum scenario for corn is that every seed that is planted emerges on the same day; there are no skips and doubles and that the plant-to-plant spacing is uniform. Even with the best of conditions and equipment, achieving perfect uniformity of emergence is unlikely. The warmer than average May temperatures this year hastened emergence and in many cases reduced

variability in the timing of emergence (cold, stressful conditions seems to accentuate poor uniformity in emergence). Nevertheless, I have still observed instances where poor uniformity will take a toll on yield.

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A few years ago, a number of Area and County Extension Agents assessed plant stand uniformity and measured its impact on yield in farmers’ fields in North Dakota (the full report of this work is available in the thesis by Lindsey Novak). They found that within a planter width, averaged over all the fields evaluated, the most variable row yielded 9 bu per acre less than the least variable row (Table 1). The most common problem causing the variability was variability in emergence date and not skips and doubles. In fact, doubles were rarely observed.

When measuring the yield loss on a plant basis, skips were the most impactful, followed by plants emerging 11-17 days after the early emerging seedlings (Table 2). Plants next to a skip could add 10% greater yield when compared to normal spacing, but this was much less than the 50% needed to totally compensate for the lost plant. Plants next to late emergers were able to add 5% greater yield, but again, they could not completely compensate for the loss of production by plants emerging later. Though there is no management practice that can ameliorate uneven stands after emergence, determining the cause of poor uniformity can be a useful learning exercise for future years. On average, most farmers will plant 40 crops in their lifetime. Learning from each crop is important to a successful operation (I learned this year not to plant a corn hybrid trial after sugarbeets unless I manage for fallow syndrome!).

When evaluating stand uniformity, expect a few skips that are caused by non-viable seeds (the range in germination for most commercial seeds lots is 90-95%). Doubles can be traced back to a planter problem. Though doubles generally do not result in a yield reduction (data not shown), they are not an efficient use of seed. Determining what caused poor uniformity in emergence timing may not be easy, but the following are some known causes that should be considered:

  • Differences in access to soil moisture by the seeds. Cloddy soils (tilled when too wet), dried or compacted soils (from too much tillage), non-optimal seeding depth, improper press-wheel tension, hairpinning of residues that results in the seed being placed next to crop residue rather than soil, and sidewall compaction are a few potential reasons why seeds have access to differing amounts of moisture during germination. Excessive speed while planting
  •  can impact the uniformity in planting depth, especially in the larger planters.
  • Soil crusting. Crusting most often results from tilled soils high in silt that received a substantial rain after planting.
  • Difference in soil temperature. Small difference in the temperature that the seed encounters can be caused by difference in depth of seeding and the amount of residue that is retained directly above the seed.
  • Seed lot vigor. Though it is not common to be overly concerned about the quality of the corn seed that is planted, seed lots with poor vigor can potentially cause variability in emergence timing. This is likely to be a concern only when there has been additional stress during germination, like cold soils.

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Joel Ransom

Extension Agronomist for Cereal Crops


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