Corn yield results not from the number of plants in a field but rather the number of ears — photocopied ears of sufficient length and girth. Gaps in a stand and plants without ears contribute nothing to yield, and late-emerging plants function like weeds.
Monitor ear development from emergence through harvest, says Farm Journal Field Agronomist Ken Ferrie. Commit to season-long scouting and consider these tips for evaluating ear development:
1. Set a goal.
“The industry standard is a 13% drop from the number of seeds planted to the number of ears you harvest,” Ferrie says. “But some growers cut that difference to 6%. That might not be every year on every field, but often enough to make it a target. When they fail to achieve their goal, they know how to make adjustments.”
2. Take stand counts and check uniformity after emergence.
Hitting your ear-count goal starts with a picket-fence stand. “Take stand counts in every field and for every hybrid,” Ferrie says. “Take multiple counts, over various soils and topography, such as sidehills and hilltops. Record the results by location.”
If you did not achieve your desired stand count in a field, take a look at the low soil temperature for the week of planting and the week after, the amount of rainfall and seedbed conditions.
If plants are missing, this will be your only opportunity to document the cause before the seeds rot in the ground. Look for evidence of disease, insect damage or poor seed quality.
“Any plant one or more leaf collars behind its neighbor won’t produce an ear,” Ferrie says. “Figure out why that plant emerged later.”
3. Scout again at the start of the rapid growth period.
That will be around the V8 growth stage. “Plants with problems won’t keep up with good plants during the rapid growth period,” Ferrie says. “Document the cause, such as sidewall compaction, pinch row compaction, anhydrous ammonia burn or green snap.”
Problems at the start of the rapid growth period can put a plant far enough behind to lose its ear, he says, even if it emerged uniformly with other plants.
4. Revisit fields at pollination.
“At this stage, you can start to get an accurate ear count and see the effect of late emergence,” Ferrie says. “Stalks two-thirds or less the diameter of their neighbors usually won’t produce an ear or will have only a very small one. A small-diameter stalk means something happened early in the plant’s development, during the planting window.
“Normal-diameter stalks with small or missing ears indicate a problem in the reproductive stage, such as disease, insects, aphids or green snap. You should know the cause from your earlier scouting; but if not, there still is time to sleuth it out.”
5. Make a final stand and ear count after black layer.
You can do this as you are evaluating stalk quality to prioritize harvest. “Compare the results to earlier counts,” Ferrie says.
This is the time to count kernels and measure ear girth and length. “With this information and a yield map you can see how many kernels were in each bushel,” Ferrie says. “Hybrids can range from 50,000 to 90,000 — or even more — kernels per bushel of harvested corn, depending on growing conditions and management. Knowing, for example, that a hybrid can produce a bushel on 50,000 kernels will give you confidence if, some year, you need to reduce population because you’re planting into soil with low water-holding capacity.
“If low ear count is preventing high yield, identify the cause and correct it,” Ferrie concludes. “Other changes, such as planter attachments or applying a fungicide, might help, but they won’t solve the problem if the underlying cause is poor ear count.”
The Components of Corn Yield
“We often speak of picket-fence stands and photocopied ears,” says Farm Journal Field Agronomist Ken Ferrie. “Picket-fence stands result from seed distribution. Photocopied ears result from growth and development. These two components are where yield comes from. Evaluating your stand provides foundational knowledge to help you increase ear count and maximize yield.”
