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Dr. Dan Talks Agronomy
Friday, August 28, 2015 10:56AM CDT

By Dan Davidson
DTN Contributing Agronomist

Driving around parts of the Corn Belt the last two weeks, I have seen fields of corn going into their end game. Many of them seem to be aging a bit prematurely -- taking on a light yellow appearance, which indicates senescence is probably just around the corner. My guess is it's also denting prematurely after laying down a bit less starch.

It has been quite the season with a lot of rain early on that delayed planting, and for a long while, it seemed it would be our constant companion all summer. However, that changed this past month for many areas of the Midwest when the weather got drier and warmer.

You've all heard that rain makes grain, but the overabundance of it this year has influenced corn in some not-so-subtle ways. One of the first visual clues we saw was yellowing due to loss of nitrogen from leaching and denitrification. Some corn yellowed prematurely and stayed that way pretty much the whole season. In other fields, this premature loss of some nitrogen didn't show up until grain fill in August.

However, I think the biggest culprit in this early dying corn is likely rooting depth. When it rains a lot in June and July, crops can get all the water they need near the soil surface. When conditions turned drier and warmer in August, the plants had already transitioned to reproduction, and producing and maintaining roots was no longer a priority. A corn plant that didn't deep root by Aug. 1 is no longer inclined to do so. The agronomist in me wishes each year for just enough rain in June to maintain the crop while forcing it to put down deeper roots. This early investment in roots in June pays off in August during grain fill.

I asked University of Illinois agronomist Emerson Nafziger for his opinion on the early die off in corn. "We've had about 2,700 GDD (growing degree days) since April 1 here, and there are some earlier hybrids that were planted early enough to be at or approaching maturity now," Nafziger said. "If a whole field is uniformly losing canopy color, I suspect that's what's happening."

However, he added that if yellowing is only appearing in parts of fields, he attributes that to undersized root systems in the more drought-prone parts of fields. "I expect kernel size and weight has been reduced by this in fields where there are still areas with some green husks or leaves. The cool weather this week might extend this difference longer than if it were hot and dry."

Shallow-rooted corn will likely have a reduction in starch deposition in the kernel and some reduced test weight and yield. Earlier-planted corn got a head start on root development and probably weathered this phenomenon better than corn planted in a more conventional timeframe.

For some other thoughts on why corn dies prematurely go to: http://www.ipm.iastate.edu/…



Dan Davidson can be reached at AskDrDan@dtn.com

Follow Dan Davidson on Twitter @dandavidsondtn


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