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Extension > Agriculture > Crops > Corn Production > Planting > Agronomic responses of corn to planting date and plant density

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Agronomic responses of corn to planting date and plant density

Jeff Coulter, Extension Corn Specialist, University of Minnesota

Good planting decisions are critical for profitable corn production

Few decisions for corn production are as important as those related to planting. Hybrid selection, row width, planting date, and planting rate can influence corn yield and net return. Decisions related to planting rate are especially important, since seed represents about 15% of the total cost of corn production (Duffy, 2013).

Hybrid selection influences corn yield more than most other agronomic input decisions

Each year in trials conducted by the University of Minnesota where numerous commercial hybrids are evaluated at multiple locations, the top 10 yielding hybrids routinely average at least 40 bushels/acre more than the lowest 10 yielding hybrids at a given location (Table 1). Similar results occur in comparable hybrid trials conducted at other locations in the U.S. Corn Belt and southern Canada.

Table 1. Corn grain yield for the top– and bottom–yielding hybrids in the University of Minnesota corn hybrid performance trial at Morris, MN from 2006 to 2013.

Top 10 hybrid entries
Bottom 10 hybrid entries

Difference between top 10 and bottom 10

Hybrid entries
Relative maturity range of hybrid entries
---------grain yield, bushels/acre--------- number ---days---
2006 217 168 49 145 90 – 105
2007 209 147 62 162 90 – 105
2008 223 167 56 134 90 – 105
2009 184 123 61 120 90 – 105
2010 202 150 52 96 90 – 106
2011 218 151 67 79 90 – 106
2012 – – – – – – – – – – – – – – –
2013 186 141 45 83 90 – 105
No trial at this location in 2012.

When selecting hybrids, it is best to choose hybrids that have performed well in multiple trials in a region. Consistent performance in multiple trials with different soil and weather conditions is critical because we cannot predict next year’s growing conditions. A hybrid that performs well in multiple trials in one year has a high potential for performing well in the same region in the following year. Grain yield with late–maturity hybrids is typically a few percent higher than that with mid–maturity hybrids, but the potential for modest increases in yield needs to be weighed against higher grain moisture at harvest. This becomes especially important in years when planting is delayed or when air temperatures during the growing season are cooler than normal.

Timely planting when there are good soil conditions – the foundation for success

Maximum corn yield is generally obtained when planting occurs in late April or early May (Table 2). In years when spring arrives early, a mid–April planting date also will produce similar yield if young plants are not damaged by a freeze in May. In years when there are few growing degree days during late April and the first half of May, maximum corn yield also can be obtained when planting occurs in mid–May.

Typically there is a rapid decline in corn yield as planting is delayed beyond mid–May. However, advantages from timely planting according to the calendar can be negated if planting occurs when soils are too wet. When corn planting is delayed beyond the third week in May, switching late-maturity hybrids to earlier–maturity hybrids reduces the risk of corn freezing in the fall before it has reached maturity. Research from Illinois and Minnesota indicates that the optimum final plant population for corn is not affected by planting date (Nafziger, 1994; Van Roekel and Coulter, 2011).

Table 2. Corn grain yield as affected by planting date in
southern and central Minnesota.

Planting date
Study 1 –
Lamberton, MN
Study 2 –
Lamberton, Morris, and Waseca, MN
-----grain yield, % of maximum-----
April 20 99 98
April 25 100 99
April 30 100 100
May 5 99 100
May 10 98 99
May 15 95 98
May 20 92 95
May 25 87 92
May 30 82 89
June 4 76 84
June 9 69 79
Data from Bruce Potter and Steve Quiring, University of Minnesota.

Optimum planting rate differs with hybrid relative maturity and growing conditions

Planting rates of 34,000 to 36,000 seeds/acre maximize net return in most fields. Optimum planting rates tend to be near or above the high end of this range for early–maturity hybrids (96–day relative maturity or earlier, and especially for hybrids less than 90–day relative maturity) (Table 3). While optimum planting rate differs somewhat among hybrids, hybrid selection generally impacts yield more than fine–tuning planting rate by hybrid.

Table 3. Average economic optimum corn planting rate by hybrid
relative maturity.

Hybrid relative maturity Number of hybrids Average economic optimum planting rate†
days seeds/acre
72 – 89 11 35,300
92 – 96 9 34,100
97 – 99 8 32,700
101 – 103 11 31,300
104 – 106 13 32,500
107 – 109 11 31,700
110 – 112 12 31,900
113 – 115 19 30,900
116 – 120 9 29,600
For the 150–200 bushel/acre yield level for hybrids beginning the the ‘P’ designation, $4.50/bushel, and $225/80,000 seeds.
From DuPont–Pioneer’s planting rate estimator:

The economic optimum planting rate for corn is related to yield level. Research in the U.S. Corn Belt has shown that the optimum planting rate increases by about 800 to 1,000 seeds/acre for each 10 bushel/acre increase in yield level. Too high of a planting rate generally does not reduce corn yield, but does reduce net return. In recent trials in northwestern Minnesota where growing season rainfall was just 10 to 15 inches, grain yield ranged from 100 to 130 bushels/acre and was not reduced with final stands up to 44,000 plants/acre.

Optimum planting rate and corn grain yield generally are not affected by row width for mid– to late–maturity corn hybrids (Van Roekel and Coulter, 2012). However, early–maturity hybrids (less than 90–day relative maturity) planted in northwestern Minnesota produced 4 to 5% higher grain yield when planted in rows narrower than 30 inches; these early–maturity hybrids also had optimum planting rates that were 3,500 seeds/acre greater when planted in narrow rows (Coulter and Shanahan, 2012).

Management summary


Thanks for the Minnesota Corn Growers Association for funding this research


Coulter, J., and J. Shanahan, J. 2012. Corn response to row width, plant population, and hybrid maturity in the far northern Corn Belt. Field Facts 12(5):1-3. DuPont-Pioneer, Johnston, IA. Available at

Duffy, M. 2013. Estimated costs of crop production in Iowa - 2013. File A1-20. Iowa State Univ. Extension, Ames. Available at

Nafziger, E.D. 1994. Corn planting date and plant population. J. Prod. Agric. 7:59-62.

Van Roekel, R.J., and J.A. Coulter. 2011. Agronomic responses of corn to planting date and plant density. Agron. J. 103:1414-1422.

Van Roekel, R.J., and J.A. Coulter. 2012. Agronomic responses of corn hybrids to row width and plant density. Agron. J. 104:612-620.

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