Extension Corn Agronomist
Field work just around the corner, and now is the time to re-evaluate agronomic decisions related to corn planting. With support from the Minnesota Corn Growers Association and others, we have been able to conduct a number of trials to determine how corn yield responds to plant population for various situations in Minnesota.
In 2008, research was conducted at Lamberton and Waseca, MN to determine how planting date impacted optimum plant population. In this study, the economically optimum plant population was not consistently influenced by planting date (Figure 1). However, yield potential was greatest with early planting, and the optimum plant population with the early planting date was 2,400 plants per acre higher than that with the mid-May planting.
Figure 1. Corn response to plant population for three planting dates. Data are averages from Lamberton and Waseca, MN in 2008. Red triangles indicate the optimum plant population based on a corn price of $4.00 per bushel and a seed cost of $250 per 80,000 seeds.
From 2005 to 2007 at Lamberton and Waseca, MN, corn plant population was evaluated in 20- and 30-inch rows for a single full-season hybrid (Figure 2). In this set of trials, there was no yield increase with narrow rows at any plant population, and the economically optimum plant population was similar (within 1,000 plants per acre) for both row widths. In 2008, these trials were repeated with four hybrids. Averaged across hybrids and locations, yield response to plant population was similar for both 20- and 30-inch rows (Figure 3), supporting the results from 2005 to 2007. However, yield with 20-inch rows in 2008 was consistently 9% higher than that with 30-inch rows for all hybrids. It is unclear why there was an advantage to narrow rows in 2008, but not in 2005 to 2007.
Figure 2. Corn response to plant population for two row widths. Data are averages over Lamberton and Waseca, MN from 2005 to 2007. Red triangles indicate the optimum plant population based on a corn price of $4.00 per bushel and a seed cost of $250 per 80,000 seeds.
Figure 3. Corn response to plant population for two row widths. Data are averages over four hybrids at Lamberton and Waseca, MN in 2008. Red triangles indicate the optimum plant population based on a corn price of $4.00 per bushel and a seed cost of $250 per 80,000 seeds.
Of the four hybrids evaluated in the row spacing study in 2008, two hybrids had a relative maturity (RM) of 94 and 96 days, and the other two hybrids had a RM of 102 days. Averaged across locations and row widths, the economically optimum plant population was 3,400 plants per acre higher for the 94 to 96 day RM hybrids than for the 102 day RM hybrids (Figure 4). Since earlier-maturing hybrids tend to be shorter and have less leaf area than full-season hybrids, it is possible that they may require higher plant populations for optimum light interception. However, we did not find that one of the maturity groups or hybrids was better suited to narrow rows than the others.
Figure 4. Corn response to plant population in 2008. Data for each maturity group are averages over two hybrids and two row widths at Lamberton and Waseca, MN. Red triangles indicate the optimum plant population based on a corn price of $4.00 per bushel and a seed cost of $250 per 80,000 seeds.
Another consideration with regard to optimum plant population is yield potential. Using data from Illinois, Nafziger (2002) reported that as yield potential increased from 135 to 225 bushels per acre, the economically optimum plant population increased from about 25,000 to 32,000 plants per acre. In other words, the optimum plant population increased by about 800 plants per acre for each 10 bushel per acre increase in yield potential.
In the last four years, there have been a total of 34 plant population comparisons conducted in 10 experiments at Lamberton and Waseca, MN. Averaged across all of these trials, yield was maximized at 36,000 plants per acre (Figure 5), and a final stand of 32,000 to 34,000 plants per acre was necessary to maximize economic return (Table 1). With generous support from the Minnesota Corn Growers Association, we will be able to further evaluate corn response to plant population for various row widths, planting dates, and maturity groups over the next few years at multiple locations.
Figure 5. Response of corn yield potential to plant population, averaged over 34 comparisons from 2005 to 2008 at Lamberton and Waseca, MN.
Table 1. Economically optimum plant population for various seed costs and corn prices. Optimum plant populations were calculated based on data from 34 comparisons between 2005 and 2008 at Lamberton and Waseca, MN.
Corn price ($/bu)
*One unit is 80,000 seeds. Optimum plant populations do not include the extra seed needed for stand.
A more in-depth fact sheet on optimum plant population for corn in Minnesota is available at www.extension.umn.edu/distribution/cropsystems/M1244.html. Additional information on corn production from the University of Minnesota is available on our new corn website: www.extension.umn.edu/corn.
Nafziger, E.D. 2002. Corn. p. 22-34. In R.G. Hoeft and E.D. Nafziger (ed.) Illinois agronomy handbook. 23rd ed. Univ. of Illinois, Urbana.