Possible Reasons Behind Corn Kernel Uniformity
The post-pollination farmer talk in parts of the United States revolves around the potential for severe stress that might reduce kernel set or kernel size in their cornfields. Growers’ interest in this topic lies with the fact that the number of kernels per ear is a rather important component of total grain yield per acre for corn.
Poor kernel set, meaning an unacceptably low kernel number per ear, but can also occur in fields that otherwise appear to be in good shape. Good or poor kernel set is determined from pollination through the early stages of kernel development; typically, 2 to 3 weeks after pollination is complete.
Problems with kernel set stem from ineffective pollination, ineffective fertilization of the ovaries, kernel abortion, or all three. Distinguishing the symptoms is easy. Determining the exact cause of the problem is sometimes difficult.
POTENTIAL YIELD LOSS
The potential loss in grain yield caused by lower kernel numbers per ear can be estimated using the formula called Yield Component Method first described by the Univ. of Illinois. Purdue.edu posted the formula and an example, the loss of only 1 kernel per row for a hybrid with 16-row ears and a stand count of 30,000 ears per acre would equal a potential yield loss of approximately 5 bushels per acre (1 [kernel] x 16 [rows] x 30 [thousand ears per acre] divided by 90 [thousand kernels per bushel]).
They also stated that Ineffective Pollination / Fertilization Poor kernel set may be caused by ineffective pollination (the transfer of pollen from the tassel to the silks) and/or the subsequent failure of the pollen’s male gametes to fertilize the female gametes of the ovules on the cob. Ineffective pollination is characterized by an absence of noticeable kernel development. Pollination problems may be due to several stress factors, sometimes working together to influence kernel set.
Severe drought stress, heightened by excessive heat, can delay silk emergence to the extent that pollen shed is complete or nearly complete by the time the silks finally emerge from the husk. Without a pollen source, ovule fertilization cannot occur.
Persistent severe silk clipping by insects such as the corn rootworm beetle or Japanese beetle throughout the active pollen shed period can also limit the success of pollination. The simultaneous effects of severe drought stress on silk emergence can easily amplify the consequences of severe silk clipping.
Severe drought stress coupled with excessive heat and low humidity can desiccate emerged silks to the point that they are no longer receptive to pollen grain germination. Consecutive days of persistent rainfall or showers that keep tassels wet for many hours per day over several days can delay or interfere with anther exertion and pollen shed.
Exceptionally long potential ears resulting from good weather during ear size determination sometimes fail to pollinate the final kernels near the tip of the cob. Butt silks emerge first and tip silks emerge last. With oversize ears, sometimes tip silks emerge after all the pollen has been shed.
Researchers at Purdue have seen that an increasingly common hybrid trait in recent years is an aggressive silking habit that results in silks emerging from the husk leaves several days prior to the availability of pollen from the tassels. The trait is associated with drought tolerance in the sense that silk emergence delays are less likely under severe drought stress and silk/pollen synchrony is better retained. However, favorable weather during silk elongation tends to favor unusually early silk appearance that can result in silk aging / deterioration prior to the availability of pollen. The typical kernel set pattern associated with this situation is blank cob tissue near the basal end of the cobs.
Poor kernel set can also reflect kernel abortion following successful fertilization of the ovules on the cob. In contrast to ineffective pollination or fertilization, initial kernel development obviously precedes kernel abortion, so the symptoms are usually shriveled remnants of kernels that may be whitish- or yellowish-translucent.
Kernel abortion results from severe stresses that greatly reduce the overall photosynthetic output of the plant during the first several weeks after the end of pollination as the kernels develop through the blister and milk stages of development. Obvious photosynthetic stressors include severe drought & heat stress, consecutive days of excessively cloudy weather and significant loss of photo-synthetically active leaf area.
Warm nights during pollination and early grain fill may indirectly affect survival of developing kernels. Research suggests that the increased rate of kernel development due to warmer temperatures lowers the available amount of photosynthate per unit of thermal time.