Seeding rate guidelines for corn in Indiana
One of the reasons that the topic of seeding rates is a popular one in coffee shops, internet chat rooms, the farm press and crop seminars is that variable rate seeding technology is becoming more and more commonplace today as a standard accessory on modern corn planters. Another factor that spurs the interest in corn seeding rates is the not uncommon belief that today’s modern hybrids will respond dramatically to aggressively high plant populations. This belief is fueled by the harvest populations often associated with national corn yield contest winning entries, coffeeshop scuttlebutt, and encouragement from seed company sales folk.
Corn plant populations have been steadily increasing in Indiana for the past 25 years at approximately 300 plants per acre per year (Nielsen, 2013). In 2012, the estimated average plant population statewide was just over 29,000 plants per acre (ppa). Considering stand establishment success ranging from 90% to 95%, this means that the average statewide seeding rate is probably between 30,000 and 32,000 seeds per acre (spa).
Statewide increases in plant population have occurred as growers have shifted from quite low seeding rates to intermediate and higher seeding rates. In 1998, nearly 46% of Indiana's corn acres were estimated to have final stands less than 25,000 ppa and only 5% with final stands greater than 30,000 (Nielsen, 2013). Whereas in 2012, only 14% of Indiana's acres were reported to be less than 25,000 ppa and 50% of the acres were reported to be greater than 30,000 ppa. Among the changes that have allowed growers to steadily increase plant populations has been the genetic improvement in overall stress tolerance that has resulted in a) ear size and kernel weight becoming less sensitive to the stress of thicker stands of corn and b) improved late-season stalk health.
I began a more focused effort several years ago to evaluate yield response to seeding rates in field-scale trials at Purdue Ag. Centers and with growers around the state. As of the end of the 2012 growing season, I have completed 43 field-scale seeding rate trials and believe that I now have a critical mass of results to begin developing seeding rate guidelines for Indiana growers.
The severe drought of 2012 offers an interesting insight into the relative risk of higher seeding rates for crops under severe stress. Consequently, the results of the 43 trials are presented separately in terms of the 31 trials from 2001 through 2011 and the 12 trials conducted in the droughty 2012 growing season.