By Roger Elmore, Department of Agronomy
Ninety-two percent of Iowa's 2011 corn acreage was planted as of May 15, according to the USDA-NASS report. Our planting progress finally pushed above the five year average and approached the progress on the same date last year. A third of Iowa's corn had emerged at the time of the report. Since then, we've had a few good planting days and some warmer temperatures and sunshine. The next USDA-NASS report will likely show nearly all of our corn planted and most of it emerged.
Growing up with corn and throughout my career I've heard, and said, "You can row the corn!" This has nothing to do with braiding hair. Here's the way I understand the use of those words:
Rowing corn - A definition: The ability to observe rows of freshly emerged corn from the end of the field or as you drive by at 25, or even 55, miles per hour. It is a remote measure of crop growth.
Perhaps it's a big deal because it denotes a milestone for the crop and marks, hopefully, the end of the planting season at least for that specific field. Certainly it tells us there are enough plants emerged together to display long lines of green converging on the horizon. An amazing sight. No pun intended!
Figure 1. You can 'row' the corn, Story County, IA; 19 May 2011.
Time to walk fields
But, don't let the beauty of the long straight rows of freshly emerged corn lull you into contentment. This is the time to walk your fields. If something catches your eye or looks amiss, put on your CSI (crime scene investigation) hat and check it out. Count the emerged plants. Look for 'wild' variability in plant to plant spacing — small differences are less important than achieving proper plant populations. (See the articles on Planter Speed and Uniformity on the Planting page on the Iowa State University agronomy corn production Web page). Look for variation in plant emergence and size. Uniform plant emergence and plant population are far more important than plant spacing in most fields.
Dig slow-to-emerge plants or kernels in skips and compare them to earlier-emerged, neighboring plants. Ask why are they different? The answer may surprise you. Check planting depth, sidewall compaction, surface compaction, residue proximity, surface crusting, germination failure, insect feeding, mesocotyl rot, weed competition; and the list can go on and on. (See the articles on Crop Establishment and Appearance on the Early Season tab on the ISU agronomy corn production page). Perhaps the planter speed was too fast, the seed bed too wet, etc.?
Figures 2 and 3 show a row segment with four plants at different stages ranging from germinating, to VE, to V1. It takes 90 to 120 growing degree day units (GDD) from planting to emergence and another 84 GDD for every new leaf from VE to V10. With this in mind, there is about 150 GDD difference between the first plants to emerge — positions 1 and 4 - and the seed in position 2 which is just sprouting. As of week ending May 20, although normal GDD accumulation is about 13 per day, we've only accumulated about seven per day in the last week.
This slow heat unit accumulation will handicap un-emerged plants relative to those that emerged earlier and set up lower yield potential on the late emerging plants. Seed depth and/or surface residue of the two later seeds/plants - positions 2 and 3 in Figure 3 - may have differed from that of plants 1 and 4 and slowed their emergence. Fortunately there were less than 5 percent un-emerged plants in this Story County field.
The conclusions you reach during your CSI investigation may not help you now or for that matter anytime this growing season. But it will help you next year. Plan ahead!
Now is the time to walk your fields!
Figure 2. Top view of a short segment of corn row with three emerged plants (positions 1, 3 (barely emerged), and 4 (emerged) and one not yet emerged (position 2). Story County, Iowa; 19 May 2011.
Figure 3. Seeds and plants from positions 2, 3, and 4 from Figure 2.
Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production. He can be contacted by email at firstname.lastname@example.org or (515) 294-6655.