Purdue University
Cooperative Extension Service
West Lafayette, IN 47907

Effects of Uneven Seedling Emergence in Corn

P. R. Carter, University of Wisconsin
E. D. Nafziger, University of Illinois
D. R. Hicks, University of Minnesota


G.O. Benson, Iowa State University      R.R. Johnson, Deere & Co.
D.G. Coffman, Texas A&M University      R.L. Nielsen, Purdue University
                    W.J. Cox, Cornell University

Corn seedlings may emerge unevenly when soil or weather conditions are not ideal at planting. A full stand may eventually be achieved, but plants emerge at different times. This publication discusses why corn emerges unevenly, describes research that measured how much uneven emergence reduces corn yields, provides recommendations for managing uneven emerging stands, and gives suggestions for obtaining uniform emergence.

Why Corn Emerges Unevenly

Soil Moisture Variability

Uneven corn emergence is most commonly caused by variable soil moisture levels in the seed zone at or shortly after planting. Moisture at seed-depth may be adequate for seed germination and emergence in some areas of a field but not in others. Soil moisture in the seed zone can vary within a field because of differences in soil type and topography. Cloddy seedbeds caused by working the field too wet can create uneven contact between seed and soil, allowing some seeds to absorb enough moisture to germinate while others are too dry.

In many cases, some seeds planted in dry soil do not germinate and emerge until after rainfall occurs, which could be several weeks after planting. As a result, a field can have a mixture of taller and shorter plants, with plant size differences depending on time from planting to rainfall. Emergence time may vary between parts of fields, from one row to the next, or from one plant to the next.

Soil Temperature Variability

Uneven soil temperature also causes uneven corn emergence, especially when planting early or under reduced tillage conditions. Soil temperatures at seed-depth can vary if crop residues from reduced tillage systems are unevenly distributed, if seed depths vary, or if soil within fields varies in type and topography. Seeds planted under heavy residue or somewhat deeper than normal are exposed to cooler soil, and generally emerge a few days later than seeds planted under bare soil, or at shallower depths. The negative effects of variable soil temperatures are particularly important when temperatures at the seed zone are near the critical 50 degree F threshold, where minor fluctuations in temperature can significantly influence germination.

Other Causes

Corn may also emerge unevenly because of variable soil crusting, herbicide injury, and insect or disease damage. Finally, uneven corn emergence occurs when corn growers replant damaged fields by "filling in" the existing stand, rather than tearing up the field and starting over.

How Uneven Emergence Affects Grain Yield

Competition from larger, early-emerging plants decreases the yield of smaller, late-emerging plants. Research was conducted in Illinois and Wisconsin to measure the extent of yield loss and to help answer the following questions.

Details of Field Study

To answer these questions, the researchers simulated uneven emergence by creating stands of corn with different emergence dates within rows.

Figure 1. How Uneven Emergence Affects Grain Yield. Grain yields are shown as percentages of the maximum yield of 187 bu./a. obtained with even emergence of a full stand (26,000 plants/a.) with early planting. Yields are averages of studies with two corn hybrids in seven environments in Illinois and Wisconsin.

The stands shown in Fig. 1 include the following planting patterns:

To imitate emergence delays, corn was planted either 1 1/2 weeks (medium) delay) or 3 weeks (late delay) after the early date (no-delay) (see Fig. 1). To assess within-row uneven emergence, repeating patterns of in-row planting time were used for each of the two delayed plantings. These patterns produced 1/4, 1/2, and 3/4 delayed plants within the stand.

For stand loss, the same repeating patterns were used but with blanks rather than delayed plantings, producing stand losses of 1/4, 1/2, and 3/4 (Fig. 1). Grain yield and growth responses were similar for the seven environments in which the study was conducted; the combined results are presented in Fig. 1.

Effects of Uneven Emergence

When the planting delay was 1 1/2 weeks (medium delay), mixed early and delayed plantings within a row decreased yield by 6 to 8% (Fig. 1). Similarly, a 1 1/2 - week delay in planting the entire stand decreased yield by 5%. A 3-week delay (late delay) in planting 1/4 of the plants within the row decreased yield by 10%. Again, a 3-week delay in planting the entire stand decreased yield by about the same (12%). A 3-week delay in planting 1/2 or 3/4 of the plants within the row resulted in a yield loss of 20 to 22%.

Effects of Stand Loss

Stand losses of 1/4, 1/2, and 3/4 decreased grain yields 10, 30, and 51%, respectively (Fig. 1). The benefit of late-emerging plants within a stand can be assessed by comparing yield percentages of uneven emergence vs. stand loss. For example, when 1/4 of the plants were planted 3 weeks late, yields were 90% of maximum, the same yield obtained under a 1/4 stand loss. This indicates that the presence of late plants did not contribute to overall yields. However, when 1/2 of the plants were planted 3 weeks late yields were 80% of maximum, 10% higher than the yield under a 1/2 stand loss. This indicates that the presence of late plants helped overall yields.

Recommendations for Dealing with Uneven Emergence

The first step in following the recommendations is to determine the general pattern of non-uniform emergence. Patterns will vary from field to field as well as within parts of fields. You should manage particular fields or parts of fields according to the most prevalent emergence pattern.

Should Late-Emerging Plants Be Protected During Row Cultivation?

Should You Replant Stands with Uneven Emergence?

Should You Fill in a Poor Stand?

Other Considerations

Recommendations for Avoiding Uneven Emergence

Corn sometimes emerges unevenly because of environmental factors that corn growers cannot control. Nevertheless, the following management practices can help you avoid uneven stands.


[1] Carter, P. R., and E. D. Nafziger. 1989. Uneven Emergence in Corn. North Central Regional Extension Pub. No. 344.

[2] Ford, H. J. 1987. ``Uniform Stands: How Important Are They?'' Crop Soils 39(7):12-13.

[3] Johnson, R. R., D. R. Hicks, and D. L. Wright. 1985. ``Guidelines for Making Corn Replanting Decisions.'' National Corn Handbook Publication NCH-30.

[4] Nafziger, E. D., P. R. Carter and E. E. Graham. 1991. ``Response of Corn to Uneven Emergence.'' Crop Science 31:811-815.

New 5/92

Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U.S. Department of Agriculture Cooperating. H.A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30, 1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access to our programs and facilities.