Agronomic responses of corn to planting date and plant density
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
|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.
|Study 1 –
|Study 2 –
Lamberton, Morris, and Waseca, MN
|-----grain yield, % of maximum-----|
|†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
|Hybrid relative maturity||Number of hybrids||Average economic optimum planting rate†|
|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: https://www.pioneer.com/home/site/us/agronomy/tools/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).
- Select corn hybrids carefully. Choose hybrids that have performed well over multiple locations in a region. Select hybrids with relative maturities that balance yield potential and grain moisture at harvest.
- Timely planting is critical, but avoid planting into wet soil conditions. High corn yields can still be obtained if planting is delayed until mid–May. Consider earlier–maturity hybrids when planting is delayed beyond the third week of May. When corn is planted into good soil conditions, optimum planting rates generally do not differ with planting date.
- 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) and/or high–yield environments. Too high of a planting rate generally does not reduce corn yield, but it does reduce net return.
- For mid– to late–maturity corn hybrids, optimum planting rate and yield generally are not affected by row width. For early–maturity hybrids (especially those less than 90–day relative maturity), narrow rows can provide modest increases in grain yield when compared to 30–inch rows; the optimum planting rate for these early–maturity hybrids has been around 3,500 seeds/acre higher when planted in narrow rows.
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 https://www.pioneer.com/home/site/us/agronomy/library/template.CONTENT/guid.54DED3F4-C686-D964-C200-4D0DC9268F99
Duffy, M. 2013. Estimated costs of crop production in Iowa - 2013. File A1-20. Iowa State Univ. Extension, Ames. Available at http://www.extension.iastate.edu/agdm/crops/pdf/a1-20.pdf
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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