Pay attention to the little things. The promise of outstanding yield can be enticing, but experts point to myriad decisions made before and during the growing season that can nibble away at final corn  yields.
Some of these decisions impact yield immediately, while other decisions made in the heat of the growing season can progressively diminish final corn yields. It’s those slow leaks that can add up to some significant yield hits.
Think about what goes into a bushel, and what it takes to lose a bushel of corn. On average, experts estimate that about 90,000 kernels make up 1 bu. and there are about 600 kernels/plant. So the loss of 150 plants in a field of 30,000 – one half of 1% – can mean 1 bu. lost.
We’ve identified some of the key management areas where producers can lose corn yield through the growing cycle and estimated an average yield penalty that could occur with even the slightest production hiccup.
And while there are maximum yield penalties that can occur with any management decision (for example: a poor stand requires a total replant), it’s the slight yield penalty hits that can reduce the overall yield potential of the field. A bushel here, a bushel there and pretty soon you’re talking about real yield.
“Those leaks are not additive, but they are subtractive,” says Joe Lauer, University of Wisconsin  corn specialist. “Adding these all up will not get you 300% of your normal yields. But, they can subtract yield from 100%.
“Good corn production is also about planning and timing. Having a plan and executing it at the right time can benefit final production,” he says.
Decisions made before planting can significantly impact final yield goals before a single seed is ever planted.
Poor HYBRID SELECTION : Yield swing of up to 30%; average 12% yield hit.
Gauging hybrid performance can be difficult, but data from the University of Wisconsin has not only tracked how hybrids have performed in yield trials from year to year, but how those hybrids perform the next year, as well.
University of Wisconsin data shows that if you take yield data from the top performing hybrids from the previous year, the difference between the best and worst has averaged from 8 bu. below average to 16 bu. above average. “This data shows that it is important to select hybrids based on consistent performance and multiple years of yield data,” Lauer says.
Plant density not optimal: Yield swing of up to 22% yield loss; average 3% yield hit.
Corn yield is a numbers game: the more plants in a field, the more ears. And the more ears, the more grain. Hitting the sweet spot – optimal corn plant density to match field characteristics – can help push yield higher. But missing that number even slightly can impact yield, by as much as 3%. “Plant population  can fundamentally impact yield,” Lauer says. “And there’s really only one time you can get it done right – at planting.” And that key decision is made when setting up the planter .
Crop rotation: Yield swing of up to 30%; average 10% yield hit.
Years of corn-on-corn rotation can clearly impact overall yields, especially when the corn crop is subjected to weather stresses. In general, data show that a 10-15% yield penalty is incurred when corn follows corn. Spring management decisions made during the rush of the growing season can have a compounding impact on yield.
PLANTING DATE : Yield swing of up to 30%; average 3% yield hit per week delayed.
Data show that planting later than the optimum planting date can cut yields by a minimum of 3% per week. The later the planting date, the more rapid the yield penalty accelerates. “Planting dates can be greatly impacted by weather,” says Roger Elmore, Extension corn agronomist at Iowa State University. “But our data show that each week planting is delayed, yields can be reduced by 3% to as much as 5%.”
Lauer says planting date sets up the entire growing season. “So it’s imperative to be ready to plant when the time is right,” he says.
WEED CONTROL : Yield swing of up to 100%; average 7% yield hit.
While total field loss due to weed pressure can be one extreme, producers often see slow yield losses due to allowing weeds to get out of hand. Miss a few weeds in the field? Waiting to control weeds, either by design or because of weather delays, can nip significantly at corn yields. Sure, weedy fields can’t produce, but applying when weeds are larger can also hurt the developing plant. And even though a field may be clean at the end of the year, the damage (lost nutrients, moisture) is already done.
LATE EMERGENCE : Yield swing of up to total replant; average 6% yield hit.
Uniformity throughout the field, from emergence to pollination to harvest, is vital for great yields. If half of the plants are about a week – or two leaves – behind the others, you will impact yield. And late emergence, even in parts of the field, can be a real yield robber.
“Planting too fast, in wet conditions, or into a poor seedbed can delay emergence,” Elmore says. “And those plants that start out late may not have a chance to catch up.”
Elmore says observations in a field near Iowa State during the 2008 growing season showed just how much late emergence can impact final totals. “Clearly 20% of the plants in the field were runts,” he says. “It was a clear pattern through the field, and could be traced to the producer going too fast with the planter and those seeds from the runt plants were planted too shallow. It may not have seemed significant at planting, but it clearly impacted final yields.”