May 22, 2011 by Jacob Bates, CCA
Over the last week we have begun to see our corn crop emerge from the soil. Overall the conditions have been fairly warm and dry throughout much of our region. These conditions would lead you to believe that emergence would also be fairly uniform. Unfortunately, we are seeing a lot of uneven emergence across Western Iowa. I first saw this in great detail on Tuesday in north central Iowa. Since then I have seen these same symptoms and received phone calls describing this across much of Region 7's territory.
Most of the uneven emergence that we are seeing now is for corn planted April 29th to May 7th. The majority of our crop was planted during this stretch. So far fields have tended to be field cultivated and from the road, emergence may look okay. However, once you get out into the field you will begin to notice gaps like the picture below.
Cause of Uneven Emergence
These gaps in stand I am attributing to pockets of extremely dry soil. Remember that corn needs to absorb 30% of its weight in water before emergence will begin. The dry weather that we experienced between April 29th and May 11th allowed us to get a lot of work done. In that stretch there was a couple very warm days on May 9th and 10th...someplaces touched 100 degrees. These temps coupled with strong winds dried things out very quickly. Seeds that sat in dry soil did not begin to sprout like others in moist soil and are now behind. From taking stand counts, I would say that 10-15% of the kernels in some fields are late emerging due to dry soil.
For the most part the rain we began receiving on May 11 & 12th helped greatly. Without that rain we could be looking at some very serious issues. Currently the seeds that didn't emerge at first are sprouting and beginning to come through the surface. The picture below is the same spot as above but now I scraped away the soil to show the 3 other seedlings emerging. For the most part, the late emerging seeds look healthy and should make it. However, in some instances you may find some that leafed out under ground. I am attributing this to a dramatic change in temperature. Most areas touched 95-100 degrees on Tuesday, May, 10th. On Sunday, May 15th temps in most areas got down to the upper 30's. That's a change of 50-60 degrees in 5 days.
Effects on Yield
The long term effects that this uneven emergence will have on yield are still somewhat up in the air. Fields will need to be re-scouted next week to see how much difference there is in plant size. The forecast looks like we will get some heat along with the rain showers over the next few days and that is what we need. I am hopeful in a weeks time these fields will look much improved. However, in fields where there is a severe difference in plant stages, yield could suffer. Every year many different factors can take away yield. Depending on how the remaining growing season turns out this may be a non-issue or it could take the top end off of some of our fields. Continue to scout fields over the next week to get a handle on how severe this is in your area.