Increased demand for corn has generated a lot of discussion about shooting for higher corn yields. A number of farmers have achieved 200 bushels per acre and now have their sights set for 300 bushels per acre. What should Iowa farmers expect for actual yields and what management considerations should be examined to achieve high yields?
"As corn hybrids have developed, the focus has been toward increasing the stress tolerance of the individual corn plants," says Roger Elmore, Iowa State University Extension agronomist. "Corn yield potential per plant hasn't increased over the past 50 years. But the yield per acre has changed. Today's hybrid corn plants are able to withstand higher plant densities while still producing an ear. Having more plants per acre producing an ear results in higher yields."
It is critical that corn growers consider seeding rates when working to increase yield per acre. A significant portion of the observed yield increase per year is directly correlated with increased plant populations. During the previous 50 years, seeding rates have increased annually. Iowa plant populations have increased an average of approximately 425 plants per acre per year since 2001.
Is planting more seed profitable?
Although plant populations continue to increase, producers and agronomists must consider whether the yield advantage of planting more seed is economically profitable, notes Elmore. Corn seed prices have increased an average of $1.50 per acre since 2000.
Seeding rates ranging from 25,000 to 45,000 seeds per acre were studied at 10 ISU research locations in Iowa in 2006. The average optimum seeding rate across all locations was 35,000 seeds per acre. However, location played a huge role in the final yield results. The yield at four of the 10 locations significantly dropped off when seeding rate exceeded between 30,000 and 35,000 seeds per acre; whereas six of the 10 locations had highest yields from 35,000 to 45,000 seeds per acre.
However, on a side note, there were 200-bushel yields in both of these groupings. "Early season vegetative growth and the conditions surrounding pollination no doubt were factors influencing which seeding rates were best for a site," says Elmore.
"A seeding rate of 35,000 seeds per acre appears to be a good general recommendation based on the 2006 data," he adds. "However, it is imperative to consider both the field conditions and he environment when you decide which seeding rate to use."
ISU will continue seeding rate research across Iowa in 2007. The objective is to characterize the environment and field conditions to determine why some sites respond more favorably to higher seeding rates than others. "Also, we want to determine which seeding rates perform best within different row spacings, particularly 30 inch rows versus twin-row planting," says Elmore.