Yield response to plant population for corn in Indiana
A random assortment of hybrids has been used in the trials, but 13 trials were split-planter comparisons with pairs of hybrids purposefully chosen for their advertised responsiveness to population. Most of the trials have also been conducted at the farmer’s normal nitrogen (N) fertilizer rate. However, 7 trials evaluated yield response to normal and higher than normal N rates.
Overall field productivity levels of the trials have ranged from less than 100 bushels per acre (bpa) to nearly 250 bpa. Twelve of the 58 trials can be characterized as “severely stressed”, most of which occurred during the severe drought conditions of 2012. These offer an interesting insight into the relative risk of higher seeding rates for crops under severe stress. Consequently, the results of the 58 trials are presented separately in terms of the 46 trials that can be characterized as “normal” productivity (moderate or less stress) and the 12 trials characterized as having experienced “severe” stress (mostly drought).
Final stand or harvest population is rarely equal to the number of seeds that were planted per acre due to germination and/or emergence problems plus plant mortality throughout the season. Percent stand (final population divided by seeding rate) in our 58 trials averages 95%, but ranges from as low as 81% to as high as 100%. Therefore, yield response to seeding rates is more appropriately analyzed and presented in terms of yield response to PLANT populations.
Growers should routinely count plants and calculate percent stand in all their fields every year to determine whether there is room for improvement. With today’s planter technologies and seed quality, aiming for a percent stand of no less than 95% is certainly achievable. Equally important is that the knowledge of your historical percent stand allows you to convert recommended final PLANT populations to SEEDING rates.
Example: If the recommended PLANT population is 30,000 and your historical percent stand is 95%, then the targeted SEEDING rate would be 30,000 divided by 0.95 or 31,579 SEEDS per acre.
Results of the trials
“Normal” Growing Conditions. For the 46 trials characterized as experiencing a normal range of growing conditions (moderate to low stress), maximum grain yield occurred at an average PLANT population of 31,400 ppa. On the basis of a percent stand of 95%, that would translate to a SEEDING rate of about 33,000 spa.
Optimum PLANT populations varied among the 46 trials from just over 24,000 to just under 44,000 ppa (Fig. 1). However, optimum PLANT populations for 74% of the trials ranged from 28,000 to 35,000 ppa.