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Put Corn Myth to Rest

Put Corn Myth to Rest
A lesson in corn growth physiology may serve you well in the future.

Why understand how to stage corn growth? Why spend time studying how corn develops after pollination, and outlining the various stages it goes through? Bob Nielsen, a Purdue University corn specialist, believes the answer is relatively simple. The more you know about how your crop grows the better informed you will be when it comes to making management decisions which may impact the crop, including final yield.

Weather holds the ultimate ace to determining yield. But even in years like 2009 and 2010 when weather throws extreme conditions at the crop, corn goes through defined stages of growth and development. It may go through them faster or slower, and that may affect things such as yield and moisture content at harvest, but it will go through the stages all the same.

One common myth is that in unusual years, or in years when it frosts before late-planted corn matures, corn does not reach the black layer stage. That's the point at which the crop is considered to be physiologically mature.

"That's simply not true," says Nielsen. "Corn will always black layer. The moisture content at which it happens may vary, but a black layer will always form at the base of each kernel. It's the point at which the kernel is physiological mature. After that point the kernel can't receive any additional starch from the plant."

Here's why a black layer always forms, Nielsen explains. The black layer is simply a group of cells, sometimes referred to as placental cells, that form as corn finishes its' life cycle. Somewhat like in animals, these placental cells form after the embryo at the tip of the kernel is complete. The embryo will form the new seedling once the seed is placed in the proper conditions for germination to occur.

"You will find in various books that the moisture content of corn at black layer can vary from 25 to 40%," Nielsen says. Last year it was probably closer to 25%, he says.

When the crop reaches black layer on a calendar basis depends upon weather conditions within the season. The last two seasons were polar opposites, with the black layer forming early in 2010, but very late in 2009. "It bumped October when the black layer formed in many fields in 2009," Nielsen recalls. "The black layer formed, but as far as moisture dry-down, once you get to October and outside temperatures are cooler, it's much tougher for corn to dry down in the field."

Some people commonly believe that if a frost should occur and stop corn development, the black layer never forms. That's simply myth, Nielsen insists. The kernel shuts down off the signal that the plant is shutting down, and a black layer still forms. Kernels and test weight may be light in that case because the black layer formed before the plant was ready to quit pumping nutrients into the kernel.

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