Importance of Corn Stand Uniformity

• Planting skips has the largest negative impact on grain yield compared to doubles or delayed plants. 
• Doubles can increase overall potential yield due to the higher plant population; however, the yield increase may not be enough to pay for the additional seed. 
• There are 4 key components to promoting uniform corn emergence: 
  • Proper soil temperature
  • Good seed-to-soil contact 
  • No excess salt near the seed 
  • Adequately oxygenated soil 
• To promote more uniform emergence, ensure that the soil is dry enough for planting, the planter is in optimal condition, the planting depth is correct and consistent and field residue is properly managed.
  

Skips occur when the planter fails to drop a corn seed at the intended place in the row or when a seed fails to emerge as a plant. Dropping 2 corn seeds in the same place that was intended for 1 seed is referred to as a double. Plants that emerge from the soil surface later than the rest of the plants are considered delayed plants. Regardless of the cause, uneven stands can affect grain yield.  

Agronomy in Action Trials 
The Golden Harvest® Agronomy in Action research team implemented trials to determine the impact various corn stand outcomes have on yield, including skips, doubles and delays. Plots were planted at a targeted seeding rate of 35,000 plants/A in Seward, NE, and Clinton, IL.  

Seeds were either removed or planted by hand in order to achieve 5% and 10% skips or doubles. Seeds were also removed and replanted by hand either 2 or 4 days later to simulate delayed emergence (Figure 1). Doubled and delayed plants, along with the plants neighboring the skips, were harvested by hand and yield was calculated. Additional whole plots with the same imposed treatments were mechanically harvested to get a larger representative yield sample of each stand outcome in the field. 

Trial Results
Planting a double resulted in each ear in the pair producing significantly less (-17%) grain per ear than plants spaced uniformly (Table 1). However, when the grain of the 2 plants in a double were added together, the double yielded 67% greater than a single plant spaced uniformly. Additionally, the neighboring plants to each side of the double produced 8% less grain due to competition from the double.

When a skip occurred, the data showed no neighboring yield compensation for the missing plant. This differs from previous findings where the neighboring plants were able to compensate. Nafziger (1996) recorded the yield of plants next to a skip to be 15% above the control when planting 18,000 plants/A, but only 9% higher at 30,000 plants/A.¹ At 35,000 plants/A, the gap created by the skip may not be large enough to influence the neighboring plants.

A plant with emergence delayed by 2 days produced 15% less grain than a plant that emerged at the same time as the rest of the stand. The reduction in grain production increased to 21% when plant emergence was delayed by 4 days (Figure 2). The plants immediately adjacent to each side of the delayed plants produced between 3-6% more grain as these plants were able to better compete for resources compared to the delayed plants. However, the yield compensation from these neighboring plants was not enough to equal the yield achieved with a uniform corn stand. 


Whole plots that were mechanically harvested included either 5% or 10% skips, doubles or delays. A stand with 10% delay by 2 or 4 days resulted in a yield decrease of 4-5 bu/A (Graph 1). Having 10% doubles throughout a field tended to yield 3 bu/A greater than a uniform stand. However, in most cases the yield increase would not cover the additional 10% cost of seed for the double. Out of all stand treatments, skips had the largest negative effect on yield. A stand with 5% and 10% skips yielded 8 bu/A and 10 bu/A less than having a uniform stand, respectively. The yield decreases are the result of having a lower plant population. 

It is important to note that the individual ear sampling results are only a yield estimate of the subplots or stand outcome. It is unlikely that 100% of a field would have skips, doubles or delays. Realistically, many fields suffer 5-10% stand uniformity issues. Therefore, the yield impact from the different stand outcomes are reduced in the whole plots with only 5% or 10% skips, doubles or delays compared to the individual ear samples from the subplots. This study, along with previous studies, have documented the importance of a strong uniform stand (Nafziger et al., 1991).² 

Factors Influencing Uniform Stands 

1. Soil temperature: Should be near 50° F to ensure good germination. 

2. Seed-to-soil contact: Poor soil contact can cause emergence delays, which lead to inconsistent ear size on the later emerging plants. Seeds must absorb water equal to or greater than 50% of their mass to germinate.  

3. In-furrow fertilizer injury: Excess salt near the seed can cause burning and weakened seedlings which are more susceptible to pathogens. Limit pop-up fertilizer (applied directly in-furrow) to 5 gallons per acre or less. Adjusting placement to at least 2” to the side and 2” below the seed can allow fertilizer rates to be increased. 

4. Anaerobic soil conditions: Germination and growth in corn requires an adequate supply of oxygen for proper development. Field conditions that can limit oxygen to the seedling include compaction and cold spring rains that saturate and displace oxygen from the soil. 

Managing for Uniform Emergence  

Maximizing the potential of a corn field requires establishing a uniform stand. To achieve this, it is critical to individually evaluate each field and associated management practices. Here are some factors to consider: 

1. Soil moisture: Tillage of wet soil results in cloddy seedbeds which can reduce seed-to-soil contact at the time of planting, resulting in inconsistent seed germination. Planter units are also more prone to bounce in wet soil, affecting planting depth. Planting into wetter soils can cause sidewall compaction and emergence issues. Soil compaction can also limit root development and access to oxygen, moisture and fertility. 

2. Planter preparation: Worn planter parts can cause problems in achieving uniform corn stands. Worn disk openers are a major cause of poor seed-to-soil contact and can affect the target seeding depth needed to establish a uniform stand. Worn drive chains and seed meters can affect plant spacing needed to maximize plant populations and yield potential.  

3. Planting depth: Maintain a planting depth of 2”. While shallow-planted corn (planted less than 1.5”’) may occasionally emerge faster, the long-term benefits of proper planting depth outweigh the quick emergence associated with shallow planting. Shallow planting can disrupt proper nodal root development causing roots to develop at or near the soil surface where they will either not fully develop or develop slower. 

4. Manage residue: Residue from a previous crop is one of the leading causes of poor uniformity. Residue in the seed furrow can drastically reduce seed-to-soil contact and consistency of germination. It can also cause planter units to bounce, dramatically affecting planting depth and emergence. Residue will also increase variability in soil moisture and soil temperature, therefore causing variability in plant vigor and uniformity.  

Contact your Golden Harvest Seed Advisor or agronomist for more information regarding corn stand uniformity.   

Photos are either the property of Syngenta or used under agreement. 
Syngenta hereby disclaims liability for third-party websites. 

References: 

1. Nafziger, E. D. 1996. Effects of missing and two-plant hills on corn grain yield. Journal of Production Agriculture. 9(2): 238-240. 
2. Nafziger, E. D., Carter, P. R., and Graham, E. E. 1991. Response of corn to uneven emergence. Crop Science. 31(3): 811-815.