Seeding rate guidelines for corn in Indiana

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.

click image to zoom 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.

click image to zoom 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.).

On-Farm Field-Scale Seeding Rate Trials

The 43 research trials that provide the basis for the guidelines offered in this report are scattered nicely throughout the state and represent a fair range of growing conditions. However, there is a need for even more such trials to better “capture” the effects of different growing conditions on yield response to plant population. Field-scale on-farm seeding rate trials are simple to conduct, especially if your planter is equipped with GPS-enabled variable rate controls. These trials can be customized to include two or more nitrogen fertilizer rates or multiple hybrids. Such trials can also be used to evaluate yield response to plant population in different areas or “zones” within fields to help address the question about the relative merits of variable rate seeding. If you would to participate in one or more on-farm seeding rate trials with corn, please download the protocol for this at the following URL and contact me for additional information.

http://www.agry.purdue.edu/ext/ofr/protocols/PurdueCornSeedingRateProtocol.pdf

Acknowledgements

The field-scale, often on-farm, research summarized in this update has been supported, in part, by funds from the Indiana Corn Marketing Council, the Purdue Mary S. Rice Farm Fund, and the Indiana Certified Crop Adviser Program. The collaboration of the participating farmers, crop consultants, retail agronomists, county Extension Educators, and Purdue Ag. Center personnel is gratefully acknowledged.

Related reading

Nielsen, RL (Bob). 2013. Thoughts on Seeding Rates for Corn. Corny News Network, Purdue Extension. Online at http://www.kingcorn.org/news/timeless/SeedingRateThoughts.html[accessed Feb 2013].