Look at the plant in the center. It's shorter and at least one or two leaves behind its neighbors. That means it is one or two growth stages behind.
Brian Denning, agronomist for Stewart Seeds with the AIM program, says in a recent report to farmers that if there are several of these later emergers, it could be an issue for yield.
The late emergers end up competing as weeds because they seldom catch up, especially if they are two growth stages behind at the start. Since they are more like weeds, they draw nutrients from other plants to produce a stalk, and seldom produce more than a nubbin themselves.
In this particular field it was actually hard to find a plant that emerged late. Most of the emergence appeared to be uniform.
This shot is from the Crop Watch '14 field, which will be used later in the year for a guessing contest for final yield. Seed prizes for 2015 will be awarded by Seed Consultants, Inc.
There are several causes that could result in uneven germination if it was a problem on a broad scale.
Rusting can be an issue, especially if some soils crust more than others. Perhaps the seed was slow in germinating. Not every seed will germinate, or at least not at the same rate under cool conditions. This field was forced to germinate under relatively cool conditions.
If you had a number of these smaller plants scattered throughout the field relatively frequently, it might be cause for concern. In this case, since we had to hunt to find one to use as an example, obviously emergence occurred in a fairly uniform fashion. The goal is for all seed to germinate and seedlings to emerge within 24 to 48 hours.
Uneven emergence or uneven spacing should not be a concern to yield in this field, unless some outside factor affects population and takes out some plants at a later date.