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Effect of Uneven Emergence on Corn Yield Potential

Categories: PLANTING, CORN
  • Yield decreased 0.6 to 1 bu/ac for every 1% increase of total plants with delayed emergence in these trials.

  • Yield and gross revenue decreased 0.26% and $1.30/ac, respectively, for every 1% increase in late emerging plants.

  • Ear flex potential of a hybrid did not influence the response to delayed emergence.

Uniform corn plant emergence is a critical step towards maximizing genetic yield potential. When uneven emergence occurs, late emerging plants are at a disadvantage in competing for resources (e.g., water, nutrients) compared to earlier-emerged plants, resulting in smaller ears. If emergence is delayed even further, those plants often are barren, yet are still competing against productive plants for resources. While several factors that cause uneven emergence are manageable (e.g., consistent planting depth, proper seed-to-soil contact), there are still uncontrollable microenvironmental factors (e.g., soil moisture and temperature) that are difficult to fully account for, especially in highly variable fields. This article discusses what to expect for corn yield when emergence is uneven due to these microenvironmental factors.

Trial Details

Agronomy in Action Research trials were conducted at nine sites to quantify the effect of uneven plant emergence on yield. Two Golden Harvest® corn hybrids with differing ear flex ratings were planted at each location to understand if the response to uneven emergence would vary. Hybrids used included G00A97 brand (semi determinant) and G02K39 brand (flex) at early relative maturity (RM) sites (Blue Earth, MN, Bridgewater, SD, Grundy Center, IA, and Janesville, WI), and G10D21 brand (semi determinant) and G11V76 brand (semi flex) at late RM sites (Clay Center, KS, Clinton, IL, Malta, IL, Slater, IA, and Waterloo, NE).

The trial evaluated varied levels of uneven emergence based on a percentage of delayed plants at the following targets:

  1. Untreated Check (uniform emergence)
  2. 10% Delayed Plants
  3. 20% Delayed Plants
  4. 30% Delayed Plants
Range of growth stages
Figure 1. Range of growth stages caused by the seed polymer and cool, dry soils at Waterloo, NE planted on May 2. Photo was taken on May 23.

Delayed emergence of individual plants was achieved by coating selected seeds with a polymer to delay germination. The polymer was originally designed for synchronizing male-female inbred pollination in seed corn production fields. A minimum number of GDUs is required for polymer breakdown, resulting in delayed water absorption by seeds and subsequent germination. In this trial, it was applied as an overtreatment to the base seed treatment in which delayed emergence was desired and blended at appropriate ratios with seeds without a polymer (Figure 1).

Response of plant stands
Graph 1. Response of plant stands and runt plants to delayed emergence at early RM (top) and late RM (bottom) sites. Different letters indicate differences between delayed plant levels, P≤0.10.

Plant Stands and Runt Plants from Delayed Emergence

Emergence of seeds treated with the polymer, on average, ranged from one to six days, although longer delays were not uncommon. For example, delays up to ten days were observed at Waterloo, NE, due to abnormally low rainfall and poor soil moisture. Stand counts were taken at the V3 growth stage to give adequate time for complete emergence and still be able to detect the number of runts or plants one or more growth stages behind.

Actual levels of delayed plants differed between the early and late RM sites (Graph 1). At the late RM sites, the observed delayed emergence levels were 9, 15, and 21% compared to the check plots without a polymer having 3% delays. Delayed emergence at early RM sites were 6, 9 and 11% compared to check plots having 3% delays.

Dry soil conditions at Waterloo resulted in a bigger spread in emergence of polymer coated seeds resulting in multiple growth stages occurring simultaneously (Figure 1). Significant variability in ear size was observed with the different emergence timings (Figure 2). Ears with fewer kernel rows were observed when emergence was delayed ≥ 7 days. Early RM sites were planted on or after May 10, which had warmer soils that likely accelerated polymer degradation, thus reducing the amount of overall delayed plants. Due to rapid GDU accumulation at early RM sites, there was also less variability of delay timings as seen at the Waterloo site.

Yield Response to Delayed Emergence

Small decreases in final stand were seen when the targeted number of delayed plants increased but in general final plant stands were similar across treatments. Due to this, it is safe to assume that yield loss at locations was primarily due to delayed emergence rather than reduced final stand. In general, yields decreased as the percentage of delayed plants increased (Graph 2). On average yields were reduced by 0.58 bu/ac and 1.1 bu/ac for every 1% increase in delayed emerging plants at the late RM and early RM locations respectively. Although the targeted number of delayed plants were the same at late RM and early RM locations, there were fewer overall delayed plants at early RM locations, yet yields were more severely reduced for every increase in delayed plant present at those sites.

RM and late RM sites.
Delayed Plants

As an example of the potential economic loss, when you look at 9% of plants being delayed, there was an average loss of 5 bu/ac across early and late RM locations from delays which is equivalent to $25 per acre (assuming $5.00 / bu grain value).

Regression analysis found yield potential decreased linearly as the percentage of delayed plants (defined as ≥ 1 growth stage) increased (Graph 3). Specifically, it predicted a 0.26% decrease in yield for every 1% increase in plants delayed. This would result in a reduction in revenue of $1.30/ac with each 1% delay increase (assuming $5.00/bu grain value). This brief economic analysis underscores that there can be significant revenue penalties if uneven plant emergence occurs.

The ear flex ability of the hybrid did not statistically affect its response to delayed emergence. It was hypothesized that yield losses would be less with flex hybrids due to their ability to better respond to interplant competition.

Uneven Emergence

However, the data did not support this, as individual hybrid responses to varying delayed plant emergence levels were statistically similar. This indicates that growers should not expect that using a hybrid with some degree of ear flex will lessen the detrimental effect of uneven emergence if it occurs.


This trial demonstrated that stand uniformity can have a significant effect on corn yield, especially in fields planted at high populations, due to interplant competition. The results also showed that hybrids with greater ear flex potential did not consistently minimize the effects of delayed or inconsistent plant emergence compared to hybrids with less ear flex. Although we cannot control the environmental factors that contribute to uneven emergence, proper planting management (residue management, seeding depth, seed-to-soil contact), selection of seed with good early vigor and planting into soils at or above 50°F will collectively help maximize uniform plant emergence.

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Performance assessments are based upon results or analysis of public information, field observations and/or internal Syngenta evaluations.

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