While the U.S. average corn  yield has seen a consistent 1.87-bu./year average increase over the past 30 years, data suggest that top yield producers may not see that consistent rate of gain continue.
“The more we looked at the data from yield contest winners, it was clear there's something limiting yields in these highly productive environments,” says Roger Elmore, Extension corn specialist at Iowa State University. “These producers have the best of everything — genetics, management and environment. Yet data show they are not consistently yielding more than 350 bu./acre.”
And while 350 bu. isn't anything to sneeze at, consider that Herman Warsaw set the world record corn yield of 369 bu./acre on his Illinois farm in 1985. He kept that record until 1999 when Francis Childs made 393 bu./acre.
“The average U.S. corn yield continues to improve due to better genetics and better management practices,” Elmore says. “And we will see variations due to weather in any given growing year.”
Elmore has studied data from the National Corn Growers Association  yield contest  going back to the mid-1980s. And what he found was that even though average U.S. yields rose, there has been a yield plateau for top producers in top environments.
IT'S IMPORTANT TO note that the yield plateau in corn is among the very top producers. “And that is very different than the yield plateau we are seeing in soybeans , where the average U.S. soybean yields have leveled off,” notes Joe Lauer, Extension corn specialist at the University of Wisconsin.
Lauer adds that long-time research at Lancaster, WI, shows that while top growers may not be seeing significant yield changes, the same holds true for yields in low-input systems.
“We have data going back 44 years that compares yield responses with a nitrogen (N) component of 0, 50, 100 and 200 lbs./acre on the plots. Those data show that when no N is applied, the genetic yield has not changed at all in that time. So we're seeing a plateau at both environments,” he says.
The data clearly show it takes a combination of genetics and management to get good corn yields. “Genetics alone can't do it,” Lauer says. “And management alone will not continue to increase yields. The combination is important.”
The ultimate goal is to make decisions that keep the yield potential of each acre as high as possible. “Every decision has an impact on the ultimate yield,” Lauer says.
For instance, he says planting the wrong hybrid for a given field condition can impact final yield by 30%. “So if your fields can average 200-bu. corn, planting the wrong hybrid can bring those yields down to 140 bu.,” he says. “And if you aren't planting at an optimum plant population, your yields can suffer 18%.”
Missing the optimum planting date can impact yields by as much as 30%, while tillage decisions can have a 7% impact on yields.
Lauer cautions that all these factors are not additive, so the right yield and optimum planting date won't boost yields by 60%. But what they do show is the importance of each individual factor in helping determine final yield.
“Genetics set up the potential for a corn yield,” Lauer says. “And while the overall growing environment will ultimately influence that yield potential, it's the agronomic decisions that help mitigate environmental stresses that keep the yield potential high.”
ELMORE POINTS BACK to Herman Warsaw's outstanding yields to illustrate the importance of hybrid selection and environment. “Warsaw was using the same genetics that everyone could access, but he was getting outstanding results,” he says. “That is a clear indication that he was choosing the right hybrid and matching it to his growing conditions.”
Several seed companies have goals of significantly increasing corn yield in the coming decades. Monsanto  has a goal of doubling average corn yield by 2030 and Pioneer has a target of increasing corn yield rate of gain 40% by 2018.
“Our 40% is an incredibly challenging goal,” says Dave Bubeck, Pioneer  corn research director. “It will take a combination of genetics, biotechnology and agronomic improvements to reach that goal.”
What sets the exceptional corn yield producers apart is the ability to remove as many of the biotic (e.g., insects, disease) and abiotic (e.g., weather, fertility) pressures in a given growing season. “In part, what we're working to do is develop hybrids that reduce as many pressures on a plant as possible to protect yield,” Bubeck says.
Much of the low-hanging fruit, when it comes to increasing yield, has been picked. “Crop rotations, fertility management, disease control and weed control  have helped push yields higher. But to get to even higher levels we will need some tremendous advances,” Elmore says.
For a national corn yield average of 300 bu., there will obviously need to be a lot of producers over a 400-bu./acre average.
“It will require a whole sea change to double the U.S. average corn yield,” Lauer says. “And not every farmer will see those kinds of increases because some soils aren't going to be able to produce that kind of yield.”
That's not to say that significant increases can't be made. “We have very good genetics; some of the best in the history of hybrid corn,” Lauer says. “But for those genetics to reach their potential, they must be matched with optimum agronomic practices and the best environment to grow.”
IT COMES DOWN to managing each hybrid to reduce stresses that result in a loss of yield potential. “That's different than simply thinking about how to increase yield,” Lauer says. “But every hybrid has a yield potential, and producers must ensure they take the right steps to get that potential.”
From an agronomic perspective, the yield potential for any corn hybrid is at its maximum at planting, when the seed  is still in the bag. “Put in the right environment, managed the right way and fortune of good weather will allow producers to see more of that maximum potential,” says Keith Porter, agronomy services leader for Mycogen Seeds . “What we are doing is using a combination of the best genetics, newest traits and best agronomic practices to allow the genetic potential to come through.”