Corn planting date trials. Each year, personnel at the Northwestern Research and Demonstration Center establish a replicated planting date trial. The trial established this year will tell us, given the conditions that will be experienced by the crop from planting until harvest, when was the best time to plant corn in Monmouth in 2015. Over a number of years and locations, these data can be used to provide planting date recommendations to regional crop producers.
In 2015, seedlings began to emerge a little more than 2 weeks after the first corn was sown on April 1.
Freezing temperatures. Looking back at spring weather over the past 30 years, the last freeze in Monmouth took place between March 24 and May 4, with the average occurring on April 10. It should not have been totally unexpected then when air temperatures dipped below 30 °F for 6 hours in the early morning hours of both April 21 and April 23. While not every plant was affected, for many both emerged leaves had a water-soaked, collapsed appearance (Figure).
To gauge the longer-term effects of the frost damage, these plants were revisited 4 days later. Above the ground, the frost damaged leaves had dried and shriveled up (Figure). What looked very disappointing above-ground appeared much more promising below-ground. In the photo above labeled "April 27" you will see when the soil is pulled away from the damaged seedling, a long, thin, white tissue connects the seed to the growing point region of the corn plant. In corn seedlings, it is the extent of damage sustained by this below-ground growing point that determines whether or not a plant will be able to regrow after frost damage. Next to their less damaged neighbors, one can see leaves of the severely damaged seedlings beginning to emerge 6 days after the last below-freezing temperature (Figure).
Research has shown that when compared to a uniform corn stand, yield reductions of between 6 and 9 percent can occur when a portion of the plants in a field emerge later than their neighbors. This same principle is likely to apply to an unevenly frost-damaged stand of corn. If yields from the April 1-planted corn are significantly lower than those of later planted corn, the interplant competition for resources caused by an uneven stand may be one contributing factor.
Click here for a 2014 article summarizing what research has shown regarding uneven corn stands and yield potential.
Click here for a thorough article by Purdue Agronomist, Dr. Bob Nielsen describing where the growing point of corn resides at different growth stages in corn.