As planting season approaches for the eastern Corn Belt, corn growers will be making a series of important decisions, including how many seeds to plant per acre for the best potential yield.
Plant populations have been increasing in recent years; in 2012, Indiana's average was about 29,000 plants per acre. But with a variety of hybrids, growing conditions, data sets and recommendations, the seeding rate decision is far from an easy one.
"Of the many agronomic management decisions a corn grower makes each year, one would think that choice of seeding rate would be among the simplest," said Bob Nielsen, Purdue Extension agronomist. "Yet, this topic continues to garner a lot of attention in coffee shops, Internet chat rooms, the farm press and in crop seminars. So, apparently this decision is not clear-cut."
The decision is tough partly because weather conditions aside, yields are determined by a delicate series of components: plants per acre multiplied by ears per plant multiplied by kernels per ear multiplied by weight per kernel.
"On the one hand, more plants per acre should equal more ears per acre, which should be beneficial for optimizing yield," Nielsen said. "On the other hand, kernel numbers per plant and weight per kernel eventually decrease with increasing plant populations. That's not good for optimizing yield."
Part of what has fueled ongoing seeding rate discussions has been growers who believe modern hybrids can withstand the stress of higher plant populations.
Seed dealers and other input suppliers also often encourage the use of seeding rates of 35,000 or more per acre, but Nielsen said growers have to look closely at the data - which can be conflicting and confusing.
Nielsen began evaluating seeding rates in field-scale trials at Purdue Agricultural Centers and with growers statewide in 2001. At the end of the 2012 growing season, he had completed 43 trials and has since compiled data and seeding-rate guidelines for Indiana.
"Results suggest that optimum plant populations for corn grown under typical yield levels and growing conditions are in the neighborhood of 31,150 plants per acre, or seeding rates between 32,500 and 34,600 seeds per acre," he said. "The results further suggest that corn grown under moderate to severe drought stress conditions may perform best at plant populations no higher than 28,000 plants per acre and perhaps as low as 21,000 plants per acre under truly severe growing conditions."
Some of those severe growing conditions include drought, non-irrigated center-pivot corners or non-irrigated sandy fields with minimal rainfall.
Nielsen has published two articles about seeding rates and seeding rate guidelines, which are free to download:
Both articles include data comparisons, graphs and other seeding rate resources.