Uneven Emergence and Early Season Growth in Corn

  • Uneven emergence and early season growth can negatively affect corn yield potential.
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  • Adequate soil moisture, appropriate soil temperature, and proper seed-to-soil contact are important factors contributing to even corn emergence and growth.
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  • Help minimize the risk of uneven emergence by avoiding field work when soils are too wet.
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  • It is unlikely that replanting uneven corn fields will lead to an increase in yield potential.
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Impact on yield potential

When uneven corn emergence and early season growth occurs, the larger, earlier emerging plants compete with later emerging plants.  Yield potential from these smaller, later emerging plants decreases because they are unable to compete with larger plants for nutrients and sunlight.  In a Minnesota study, normal planted corn was compared to fields in which half of the seed was planted either 7 or 14 days later.  Yield from fields with delayed planted corn were reduced compared to fields with uniform corn emergence. Later emerging plants were found to have smaller stalks, smaller and fewer ears, more barren plants, and less grain per plant than corn in fields with uniform emergence.1 Table 1 illustrates percent of maximum grain yield expected from various planting dates and final plant populations, based on uniform stands.

Factors contributing to uneven corn growth

Soil moisture.

Corn seedlings may emerge at different times if soil is either too dry or too wet shortly after planting. Soil moisture can vary within a field due to differences in soil characteristics or topography. Planting at an uneven seeding depth or planting too shallow can lead to uneven soil moisture in the seed zone. A planting depth of less than 1.5 inches can increase the risk of uneven germination and emergence due to drying of surface soils.2

Soil temperature.  It takes about 119 growing degree days for corn to emerge. Corn emergence occurs in 7 days or less when soil moisture is adequate and soil temperatures are in the mid-50 °F or warmer.2  When soil temperatures are less than 50 °F, corn germination and emergence occurs more slowly and unevenly.  Variation in soil temperature in the seed zone can be caused by surface residue, differences in soil texture and color, soil drainage, and uneven seedling depth. 

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Table 1. Relative yield potential for corn with different planting dates and populations. 4

Planting Date
4/20 - 5/25/2 - 5/155/15 - 5/255/25 - 6/56/5 - 6/15
Population (ppa)% of Maximum Yield
45,000 9793856852
40,0009995866953
35,00010096877054
30,0009995866953
25,0009591836751
20,0008985776348
15,0008178715744
13;10;Seed-to-soil contact.Corn kernels need to absorb approximately 30% of their weight in water before germination begins.3 Soil must be firmed around the corn seed in order for the kernel to absorb moisture quickly and uniformly.  Uneven germination and emergence occurs when seed is in contact with residue in the seed furrow, which can occur when planting conditions are too wet for coulters to properly cut through residue.  Planting in wet conditions can lead to decreased seed-to-soil contact by preventing proper closure of the seed furrow and create problems due to sidewall compaction.  Soil clods formed by working soil that was too wet can also prevent proper seed-to-soil contact.

Additional factors.  Soil crusting, insect damage, herbicide injury, and diseases may also cause uneven corn emergence and growth.

Management considerations

Research indicates that replanting fields with variable emergence and corn plant heights rarely leads to an increase in yield potential.1 To minimize the risk of uneven emergence, avoid working soils and/or planting when fields are too wet.  Check periodically for uniform moisture and proper seed-to-soil contact during planting and adjust planter settings as necessary. In order to avoid injury to corn, especially fields with uneven stands, it is important to remember to apply herbicides based on the most advanced leaf stage in the field.