To reach maximum yields, you have to minimize the stress on a corn plant. As Farm Journal Field Agronomist Ken Ferrie puts it: Keep corn happy and never let it have a bad day.
In the quest for top yields, several variables come into play.
"In many test plots, we've just pushed populations higher to see what the outcome is,” Ferrie says. "Not only do some hybrids flatline, they go backward.”
For three years, the Farm Journal Test Plots team studied hybrid response to nitrogen (N) stress with various timed applications. Working with AgriGold Hybrids, we were able to confirm their recommendations for N timing according to hybrid family.
In 2009, we continued our work with AgriGold and launched a new plot to learn more about stress on corn plants categorized by ear type.
"We look at their pedigrees and study parent lines in and out of the field to know as much as we can about a hybrid's genetic characteristics,” says Mike Kavanaugh, AgriGold agronomy manager.
Ear types. Based on the genetic characteristics, seed companies can place hybrids in one of three categories: those that will flex the most, semi-flex and those that will flex the least.
"Every hybrid flexes, but how they flex varies,” Ferrie says. "Some flex in length, some flex in girth and most just flex in kernel depth so you get a bigger ear with the same amount of kernels.”
One of the factors farmers consider when deciding to replant is ear type.
"Farmers know that if they lose stand, a flex hybrid will fill in those gaps,” Ferrie says. "However, if a fixed ear type loses plant count, it won't be as easy for it to pick up the slack.”
Ferrie has observed that even though a flex ear can maintain its yield despite stand loss, plant stress seems to take a toll on these types of hybrids.
"When we work with population plots and push plant densities from too low to too high, the determinant hybrids climb and top out in yield and then flatten until they go down in yield,”
Ferrie says. "The flex hybrids will also go up in yield as population increases, but when they flatline, it's for a shorter span and then they drop quicker in yield compared with a determinant.”
Stressed out. Based on ear type, corn hybrids can respond differently to growing season stresses, including drought, compaction and lack of N.
With this past year's plot with AgriGold, we set out to see how flex and fixed ear types respond to stresses triggered by different plant densities and N rates.
AgriGold provided two hybrids classified as fixed ear and two hybrids classified as flex ear. The planted populations were 32,000, 34,000 and 36,000 in a 30" row configuration. The base N applied was 120 lb., and the sidedress rates were 60 lb. and 90 lb.
"The trend in our plots shows that under stress, flex hybrids will go backward in yield quicker than a determinant. A determinant has to be pushed to reach its top yield potential, but it flatlines for a longer period and won't go backward as easily,” he says.
This plot confirmed Ferrie's sideline observations: Yields for flex hybrids will decrease quicker when the corn has to deal with growing season stresses.
When looking at yield data divided into management zones by soil type, we harvested the following results.
In one of the fixed ear hybrids sidedressed with 60 lb. N, boosting population from 32,000 to 34,000 increased yield by 1 bu. from 211 bu. to 212 bu. per acre. When sidedressed with 90 lb. N, the same fixed ear hybrid (with population increased from 32,000 to 34,000) yielded 8 bu. more, pushing yield from 221 bu. to 229 bu. per acre.
In a flex ear hybrid (in the same soil type), when the sidedress rate was 60 lb. and planted population increased from 32,000 to 34,000, yield decreased 17 bu., from 238 bu. to 221 bu. per acre. When the sidedress rate was 90 lb. and the population was increased from 32,000 to 34,000, yield decreased 5 bu., from 244 bu. to 239 bu. per acre.
"In the flex ear, we were able to offset some of the yield loss with the increased N rate,” Ferrie says. "But we weren't able to completely recover it.”
In five years of observations, Ferrie has confirmed that a flex ear hybrid will go backward quicker under stress. But he doesn't think it's possible to tell how much it will go backward.
"When we stress a flex hybrid, it responds inconsistently. You just can't expect that when you increase population, yield will always follow,” he says.
Ferrie cautions farmers to not leave yield out in the field—but, on the flip side, to not just push populations and expect automatic yield gain.
"Walk before you run. Take these hybrids to your fields and put in some rounds at different populations and watch them. This becomes especially important where water may be an issue—and N, as well, like it has been for the past two years,” he says.
More than anything, Ferrie says, "choose for yield first.”
You can e-mail Margy Fischer at email@example.com.
- Late Spring 2010