Source: RL (Bob) Nielsen, Jim Camberato, & Jason Lee Purdue University (Edited)
Results from 97 field scale trials around Indiana since 2008 suggest that maximum yield response to plant populations for 30-inch row corn grown under minimal to moderate stress conditions occurs at about 32,150 plants per acre (ppa), equal to seeding rates of about 33,840 SEEDS per acre (spa). Economic optimum populations are several thousand lower than the agronomic optimum. Corn grown under extremely challenging conditions (e.g., severe drought stress) may perform best at plant populations no higher than 22,800 ppa and perhaps as low as 21,000 ppa under truly severe growing conditions (e.g., actual drought, non-irrigated center pivot corners, non-irrigated sandy fields with minimal rainfall).
The cost of seed corn is the largest single variable input cost for most Indiana corn growers(Dobbins et al., 2019). Minimizing that cost involves a combination of shrewd purchasing skills and wise selection of seeding rates. This summary focuses on our recent research evaluating the yield responses of corn to plant populations in field scale trials conducted around the state of Indiana since 2008.
Reported corn plant populations have increased steadily in Indiana (and Ohio) for the past several decades, at an annual increase of approximately 315 plants per acre (ppa) per year, based on historical data summarized by the USDA National Agricultural Statistics Service. In 2018, the average reported plant population for Indiana (and Ohio) was approximately 30,400 PLANTS per acre (USDA-NASS, 2019). Considering stand establishment success typically ranges from 90% to 95%, the average reported population suggests that the average seeding rate statewide is 32,000 to 33,800 seeds per acre (spa). Among the agronomic factors that support the steady annual increase in 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.