Seeding rate guidelines for corn in Indiana
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The relationship between yield and plant population is shown in Fig’s 1 and 2 in terms of “percent of maximum yield” rather than actual bushels per acre. This facilitates the interpretation of results from multiple trials with differing overall yield levels.
Figure 1 represents the yield response to plant population for the 31 trials conducted prior to the drought year of 2012. Surprisingly, the visual effect of plant population on grain yield is not very dramatic. In fact, the yield response is so flat that one cannot confidently calculate an optimum plant population using the entire dataset. However, optimum plant populations can be calculated for each individual trial and the average of those individually calculated optimum plant populations is 31,150 ppa. This average optimum plant population would be equivalent to seeding rates of approximately 32,500 to 34,600 spa depending on your typical stand establishment success rate.
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Calculated in the same manner, the average optimum plant population among the 12 trials conducted in the drought year of 2012 (Fig. 2) was lower, at 28,000 ppa or seeding rates of approximately 29,500 to 31,000 spa. The yield penalty for higher plant populations under drought conditions is more evident, but varied among the locations. In fact, the highest yield occurred at the lowest plant population (approximately 21,000 ppa) at three of the 12 locations. The effect of severe drought stress on optimum plant population is also evident when the optimum plant populations for each trial are graphed against the optimum yields at those locations (Fig. 3).
More importantly, though, Fig. 3 also illustrates that there is little relationship between optimum populations and yield levels ranging from the low 100’s to the low 200’s (bu/ac). This is relevant information for growers who are contemplating the merits, or lack thereof, of variable rate seeding for corn in Indiana because the results suggest there would be little value in varying seeding rates in fields with yield potentials within that range.
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Summary
Results from 43 field-scale trials around Indiana since 2001 suggest that optimum plant populations for corn grown under typical yield levels and growing conditions are in the neighborhood of 31,150 ppa or seeding rates between 32,500 and 34,600 spa. The results further suggest that corn grown under moderate to severe drought stress conditions may perform best at plant populations no higher than 28,000 ppa and perhaps as low as 21,000 ppa under truly severe growing conditions (actual drought, non-irrigated center pivot corners, non-irrigated sandy fields with minimal rainfall, etc.).
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