With corn planters  beginning to roll soon, it is a good time to think about the relative importance of uniformity of emergence and stand uniformity, says Kraig Roozeboom, Kansas State University (K-State) Research and Extension crop production specialist.
“These are two different things,” Roozeboom says. “Uniformity of emergence deals with timing. Do most plants come up at the same time, or are some delayed by several days? Stand uniformity has to do with how consistent plant spacing is within the row.”
Of those two factors, emergence uniformity is more important to corn  yields than stand uniformity, he says. Getting good emergence uniformity can have a big effect on yields. Producers should make an extra effort to ensure that most of the corn seed  comes up at nearly the same time. Many factors can come into play.
“Emergence can be delayed by having variable moisture in the seed zone, crusting, non-uniform planting depth or non-uniform crop residue ,” he says.
Research has shown that if one out of six plants is delayed by two leaf stages, yields can be reduced by 4%, Roozeboom says. If one out of six plants is delayed by four leaf stages, yields can be reduced by up to 8%. Other research has indicated that if plants emerged within a period of two weeks, yield reductions were less than 3%.
Planter speed can affect both emergence and stand uniformity, says Stu Duncan, K-State Research and Extension Northeast Area crops and soils specialist.
“Research conducted in northeast Kansas has shown that higher planting speeds reduces final plant population, and that this had a greater impact on yield than did any reductions in uniformity of plant spacing. Be sure to follow manufacturer guidelines for recommended planter speeds,” he says.
High-residue, no-till  situations can be challenging for getting uniform emergence, says DeAnn Presley, K-State Research and Extension soil management specialist.
“Uniform distribution of crop residues during harvest is essential for uniform emergence of the next crop. The use of vertical tillage, as well as chopping corn heads, are gaining popularity as ways to manage corn residue,” she says.
Presley recommends that planter units be adjusted to optimize seed placement and depth, adding that seed firmers may help place seeds more uniformly
Emergence might be delayed slightly with deeper planting, but the corn will likely emerge more uniformly than if it were planted too shallowly, Roozeboom adds
Good stand uniformity is a good goal for producers, but it has less effect on yield than emergence uniformity, the K-State agronomists say.
“Try to obtain plant spacings that are as consistent as possible, but don’t become overly anxious about it, provided the typical spacing between plants is within 2-3 in. of the desired plant spacing and the final population is not substantially lower than what was desired,” Roozeboom says.
Duncan has been studying corn plant populations and stand uniformity the past few years. His results indicate little yield reduction from non-uniform stands as long as the final population is within 15% of the target population.
More information is available at county or district Extension offices or in the K-State publication C-560, Corn Production Handbook, available as a PDF download .