Understanding Ear Flex

Each hybrid starts the season with the genetic potential to produce a certain size ear with a certain number of kernels. The hybrid flexes ear and kernel size downward to match the amount of starch it produces. ( Lindsey Benne )

The key to benefiting from Variable Input Technology (VIT) is to plant the ideal hybrid in each soil management zone, then manage each one appropriately. Understanding how each hybrid flexes its ear size, based on growing conditions, helps you pick the best planting date and population, and plan your fertility program and disease management.

Studies conducted by Farm Journal Field Agronomist Ken Ferrie are shedding new light on how various hybrids flex their ears, and on how to manage each type. Through photosynthesis, each plant produces a certain amount of starch, and your goal is to ensure there are enough kernels to store all of it. Ear flex is a major factor influencing the number and depth of kernels—the more kernels, and the bigger they are, the more starch you can haul over the scale.

“The total amount of starch stored per acre is a function of the number of ears, the number of kernels and the amount of starch per kernel,” Ferrie explains. “Those characteristics are affected by the plants’ ability to flex ear size based on their environment.”
Let’s review the basics of ear flex:

  • “The more starch a corn plant produces, the more it puts into its ear,” Ferrie says. “A plant by itself, at the edge of the field, with abundant sun and water, will produce a larger main ear and a decent-sized second ear. If you don’t let it put on a sucker or second ear, it will produce the largest ear genetically possible.”
  • The upper limit for ear length, kernel count and kernel depth, for every hybrid, is set by genetics. When crowded and competing for water and sun, or under other stress, hybrids will flex their ear size downward.
  • That’s the only direction ears will flex: down. “Farmers sometimes say they like a hybrid because it flexes out a big ear,” Ferrie says. “But that ear size will go down if the amount of starch per plant is reduced because of a higher population or adverse growing conditions.”
  • All hybrids flex their ear size, but some flex more than others.
  • Hybrids can flex three ways: in length, girth (both of which affect the number of kernels) and depth of kernel. Some hybrids use all three methods; others use only one or two.

You’ve seen ear flex at work in your field when corn was under stress. “Corn is at its maximum yield potential while it’s still in the bag,” Ferrie says. “After planting, it accepts the limitations of its growing environment. Genetically, you might have started at 22 rows of kernels around the ear. If, by the V5 stage, the plant senses too much competition or stress, it might flex to 20 rows of kernels.

“Once the plant flexes downward, it will not add back more rows of kernels if the stress is removed. Stress in the V6 through R4 stage challenges ear length. If stress is severe enough before tasseling, the plant can truncate its ear. This can result in ears filled to the tip but only 30 kernels long. Or the end of the cob might be barren. Once it truncates the cob, the plant will not lengthen its ear any further.”

Another way ears flex is to abort kernels if the plant pollinates more kernels than it can fill. “For example, you might find ears that pollinated 45 kernels per row, but aborted to 30, leaving 15 shriveled yellow kernels at the end of each row,” Ferrie says.

Ears also can flex the amount of starch per kernel. “New hybrids add bushels by increasing the amount of starch in each kernel,” Ferrie says. “That’s how we obtain yield increases without raising populations.

“So when we lose girth, we still can make up some yield through increased length and kernel size. If we lose both girth and length, we can only make up yield by increasing kernel size.”

A Farm Journal study is boosting our understanding of ear flex. “It has revealed a big difference in how various hybrids flex, in all three areas,” Ferrie says.

The study involves what you might call super-intense hybrid test plots. “We plant each hybrid at a low population of 22,000 to 24,000 plants per acre,” Ferrie explains. “We’ve learned that will produce the biggest possible ear. If we go lower, we get double ears and suckering, which confuses the results. Then we plant each hybrid at 36,000 plants per acre. At this population, the ears flex downward in size, based on starch production.”

Based on plot results, noticeable patterns have emerged. “When the population goes up, starch production per ear goes down,” Ferrie explains. “But it happens in different ways with various hybrids.

“For some, the reduced starch production per ear results mostly from a smaller girth (fewer rows of kernels around the ear). This tells us the plant senses population stress at an early stage, such as V5. This stress is not visible to the human eye.

“In other hybrids the reduction in starch production shows up in the length of the ear before tasseling,” Ferrie continues. “Those hybrids produce a shorter ear and cob. Still others show the lack of starch production after pollination, in the form of unfilled ears and aborted kernels.

“Yet some hybrids hardly change their kernel count. Instead, at low populations, they will produce an ear of 650 kernels so girthy you can’t close your hand around it. But at the high population, ears still contain 650 kernels, but you can wrap your hand around the ear and your forefinger and thumb will touch,” he adds.

Understanding how each hybrid flexes ears in terms of girth, early length, late length and depth of kernel is a key to making a profit using VIT, Ferrie says.

  • Hybrids that flex in girth and early length must be highly managed from emergence to tasseling. “Planting girth-flexing hybrids in cold, slow-growing conditions leads to lost kernels,” Ferrie says.
  • Hybrids that flex in early length can’t stand much stress during the rapid growth stage. “Water or nutrient deficiencies will shorten the ear, leaving only kernel depth to work with to increase starch storage,” Ferrie says.
  • Hybrids that flex mostly in kernel depth must be managed at the back end of the season. “Kernel depth occurs during the last 30 days of grain fill,” Ferrie says. “For those hybrids a long grain-fill period is beneficial. Moderate temperatures and high evapotranspiration rates at that time will pay dividends. We’ve seen hybrids flex 30 bu. to 60 bu. in kernel depth alone. Hybrids that gain a lot in kernel depth need water, nutrients and sun all the way to the end of the growing season. Spraying a fungicide tends to add yield even when disease is not present because the stay-green effect of the fungicide aids ear fill.”
  • Some hybrids flex in all four areas if they are stressed enough. “Those hybrids must be managed early in the season because they can’t stand many stressful days,” Ferrie says. “But because there is potential to make up some of that yield later in the season, they also must be managed all the way to the end.”  

“If there’s a weak link in your program, and you choose the wrong hybrid, you will sacrifice yield,” Ferrie says. “For example, say you’re fighting the carbon penalty in continuous corn, and your plants look tough for a few weeks early in the season. If you planted a hybrid that flexed before tasseling, this stress will be costly in terms of yield.

“But if you get through the carbon penalty by tasseling time, hybrids that flex mainly in kernel depth will lose less yield from the stress caused by the carbon penalty,” Ferrie continues.

A knowledgeable seeds rep is the only source of information on ear flex characteristics of hybrids. “But if you plant a variety plot, take it to the next level and observe the effect of two populations on ear flex,” he suggests.

“Choosing the best genetic package to fit each management zone is the first step to benefiting from VIT,” Ferrie concludes. “Understanding how hybrids flex ears will help you manage each one to obtain its highest yield.”

Seeding Rates Are All About Starch

Here’s a new way to think about plant population: “One acre of corn produces a certain amount of starch,” says Farm Journal Field Agronomist Ken Ferrie. “You need to produce enough kernels to hold that starch. Once you have enough kernels, adding more will not increase yield unless the volume of starch also increases.”

Seed company population recommendations are based on yield per acre. “Hybrids able to store large quantities of starch per ear have lower recommended populations,” Ferrie says.

Seed companies attempt the find the sweet spot in terms of population for each hybrid, Ferrie adds. “If you increase the population, you will just allocate the amount of starch across more plants and ears,” he says. “You also re-allocate the amount of available water and nutrients, and that stresses the plants.”

An Old Rule No Longer Works

Because of the ear-flex characteristics of today’s hybrids, an old rule of thumb for estimating yield no longer works, explains Farm Journal Field Agronomist Ken Ferrie.

“Traditionally, we have said if an ear of corn flexes from 18 rows of kernels to 16 that equals a loss of 20 bu. per acre,” Ferrie says. “We also said if we lost one kernel in length, we lost 5 bu. per acre.

“For that to work, 1 bu. would have to consist of a certain number of kernels. The standard is still 80,000 kernels per bushel, but hybrids range from 50,000 to more than 90,000 seeds per bushel.”

Tools are available to vary the rate of every input for every soil type in a field. Ready yourself for variable-input technology by following along with this seven-part series at bit.ly/VIT-series