Yield response to plant population 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 corn planters. Another factor that spurs the interest in corn seeding rates is the not uncommon belief that today’s hybrids will respond dramatically to aggressively high plant populations. The harvest populations often associated with national corn yield contest winning entries, coffee shop scuttlebutt, and encouragement from seed company marketing efforts fuel this belief.
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 2013, the estimated average plant population statewide (USDA-NASS, 2013) was approximately 30,400 PLANTS per acre (ppa). Considering stand establishment success ranging from 90% to 95%, this means that the average statewide seeding rate is probably between 32,000 and 33,800 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 ppa (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.
Field-Scale Seeding Rate Trials
Background on the trials
We began a more focused effort several years ago to evaluate yield response to seeding rates in field-scale trials at Purdue Ag. Research Centers and with growers around the state. To date, 58 such field-scale seeding rate trials have been completed.
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.
These trials range in size from roughly 30 acres to 100 acres. Individual plot size is typically length of field by twice the width of the combine header. All of our trials to date have been on 30-inch rows, with the exception of a couple of twin-row trials. Most trials are planted using variable rate technologies and “prescription” seeding rate files developed prior to planting with GIS software. Commercial field equipment is used for all field operations. Harvest grain yields are typically estimated with GPS-enabled yield monitors and the yield data are processed with GIS software post-harvest to eliminate any significant non-treatment field variability (e.g., wet holes, gullies, planter skips, etc.). The statistical quality of the data from these field-scale trials is typically better than we could achieve with small-plot trials in the past.
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