Assessing the results of 67 field-scale trials conducted throughout the state since 2008, Nielsen and his colleagues at Purdue determined that the maximum grain yield for a typical Indiana cornfield under normal growing conditions occurs at a final population of 32,000 plants per acre.
Last year, the estimated average plant population statewide was about 30,850 plants per acre. In 2012, half of the state's cornfields had more than 30,000 plants per acre, compared with only 5 percent in 1998.
Corn plant populations have steadily increased in Indiana over the past 25 years by about 300 plants per acre per year. Probably the biggest reason for the increase in corn population, Nielsen said, is the improved stress tolerance of modern hybrids, meaning the plants do better in densely populated fields.
Variable-rate planter technologies are another factor. Although variable-rate seeding tools have been commercially available for years, they are now becoming standard equipment on most corn planters, Nielsen said. Variable-rate seeding allows farmers to put down different rates of seed in different parts of their fields.
The field studies included a variety of hybrids and some split-planter comparisons using pairs of hybrids purposely chosen for their advertised differences in response to population, Nielsen said.
The research team - consisting of Nielsen, Jason Lee and Jim Camberato - studied cornfields throughout the state, ranging in size from 30 to 100 acres. All of the trials were conducted on 30-inch rows. Growing conditions ranged from ideal to severe stress.
Nielsen said the results indicated that under severe stress, corn does best with a final population of 21,000 to 24,400 plants per acre.
Percent stand - the number of grain bearing plants at harvest divided by the seeding rate - ranged from 79 percent to 100 percent, with an average of 96 percent. To achieve the "ideal" population of 32,000 seeds per acre, farmers should plan on putting down 32,500 to 34,300 seeds per acre, Nielsen said.
Nielsen's complete analysis is available in the report "Yield Response of Corn to Plant Population in Indiana" online.
Nielsen and the team are currently looking for farm operators willing to take part in the next round of field-scale corn population studies. For more information on the studies and how to participate, contact Nielsen at 765-494-4802, or email@example.com. Nielsen's Chat 'n Chew Café newsletter is available at http://www.kingcorn.org/cafe.