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Evaluating Corn Stands (06/25/20)

Corn growing degree days are running about normal for most of the state and far above where we were at last year at this time.

Corn growing degree days are running about normal for most of the state and far above where we were at last year at this time. Before corn plants get too big and cover the inter rows, it is a good time to evaluate stand establishment and uniformity of emergence. The ideal is that all seeds that are planted to emerge on the same day. Achieving this ideal was challenging for many growers this spring for a number of reasons. Though there is nothing one can do about plant stands at this point in the season, diagnosing problems that resulted in poor stands can potentially guide planting processes in future years so similar problems can be avoided.

The first step in evaluating this year’s stand is to determine how the established plant population compares to what was desired. The optimum plant population has been increasing in recent years. New hybrids tolerate higher populations and higher populations can partially explain the yield advances in corn that been widely documented. Plant populations greater than the optimum do not result in increased yield, however, and produce a negative economic return on the added seed cost. Regularly including some strips within a field that vary in seeding rate (preferably with replication) and keeping track of the yield from these strips at harvest can be a good way of determining if the seeding rate you are using needs adjustment. Bear in mind that the optimum seeding rate of a hybrid may interact with the environment, meaning that the optimum seeding rate one year or in a specific field may not be the same as optimum rate in another season or growing environment. A good seeding rate recommendation is based on the results of testing in multiple environments and is the rate that on average across environments consistently performs the best.

When counting plants, note the number of skips and doubles. Skips represent a yield loss as neighboring plants on either side of the gap are not able to completely compensate for the productivity of the missing plant. An occasion skip should be expected since 100% germination in a seed lot is rare. An occasional double will not adversely affect yield and may actually add to the overall yield, though the productivity on a per plant basis is much lower than the yield of a single plant that is properly spaced. A common emergence issue is variability in the timing of emergence. Corn seedlings that emerge more than a week later than neighboring seedlings will not “catch up” and will yield less than if they emerged at the same time. Seedlings that are more than two leaves behind the first plants to emerge have the potential to be barren. However, in our survey work conducted several years ago, we did not find any “very late emergers” that were barren. The overall yield loss associated with emergence variability will depend on the percentage of the plants that emerge late and the length of their delay in emergence. Table 1 summarizes the yield of single plants from samples collected in farmer’s fields under the various scenarios previously described.

The following are some known causes of emergence variability that should be considered when stands are less than ideal:

  • 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.

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Joel Ransom

Extension Agronomist, Cereal Crops

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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