arly-planted corn in Indiana is well into, if not beyond, the pollination stage. Some folks have noticed that the height of plants in these fields is noticeably shorter than they normally expect to see. The causes of shorter than normal corn can be traced back to planting date and temperature during stalk elongation.
Remember that stalk elongation begins at about the V5 stage of development (five visible leaf collars). Prior to that stage, most of the plants energy is directed to root development and leaf initiation. After that stage, the plant enters its so-called grand growth phase wherein above- and below-ground growth accelerates to an exponential pace that peaks near tasseling.
Elongation of the stalk occurs primarily by cell expansion near the bases of the internodes at what are called the intercalary meristems. Stalk elongation is influenced by a number of factors, among which are light/shade relationships, daylength and temperatures. Shade tends to increase levels of the plant growth regulator auxin, which, in turn, encourages greater elongation of internodes. The 'shading effect' contributes to the greater plant heights of densely planted corn. Intense solar radiation is thought to result in photodestruction of auxin, which leads to less internode elongation, which results in shorter plants. Interestingly, though, longer daylengths tend to increase internode lengths and overall plant height. Cold temperatures are thought to increase the rigidity of basal internode cell walls, thus limiting cell expansion and internode elongation.
Given these physiological causes of short plants, one can think about this year's corn crop and begin to understand why some of it is pretty darn short at tasseling. Indianas corn planting progress finished six days ahead of the previous record pace set in 1988. Early-planted corn normally reaches the V5 stage at dates earlier than does later-planted corn. Stalk elongation in early-planted corn, therefore, begins in a time period that is characterized by shorter daylengths and generally cooler temperatures than corn planted later in the season. As described above, both of these factors contribute to shorter internodes and plant heights.
Now consider the two- to three-week period beginning in mid-May when temperatures were significantly lower than normal throughout much of the state. Much of the early-planted corn was beginning or well within the stalk elongation period while most of the later-planted crop was younger than V5. This extended period of cool temperatures influenced the elongation of internodes in the lower third of the stalk and accentuated the expected typically shorter heights of early-planted corn.
Are there yield consequences of unusually shorter corn? There are probably no negative consequences, unless the short height is dramatic enough to significantly reduce crop canopy cover and harvest of sunlight. Conversely, shorter corn is usually a benefit from the standpoint that the risk of stalk lodging is decreased due to the lower center of gravity.