November 11, 2016
Some of you saw a good number of damaged kernels in the combine hopper at harvest this year. A favorable environment for late-season diseases in parts of the Corn Belt led to more ear rots than normal. Diplodia was a major culprit. Even ear rots that move from the cob end of the kernel out turned up this year in some fields.
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Even without disease, there will be differences in how kernels look from hybrid to hybrid. Each has the same basic parts, but there can be variations in how hard the starch is inside the kernel, the color of the outside of the kernel, and the size and shape of the kernel. All these factors can impact grain quality and possible use.
Here is a short refresher on what a kernel should look like at harvest. Part of this information comes from the Purdue University Corn and Soybean Field Guide. Thanks to Dave Nanda, a crops consultant, for demonstrating how to split a kernel and identifying the parts inside.
Black layer. Once kernels reach physiological maturity, a black layer forms at the tip. It’s more visible if you split a kernel lengthwise, as shown here. Physiological maturity technically occurs just before the black layer forms. The black layer itself is made up of placental cells that die and collapse over the opening to the kernel. At this point, the door is closed for transport of photosynthetic materials in or out of the kernel.
Sometimes it’s beneficial to know if kernels have reached black layer if a frost is threatening. If corn matures before a frost occurs, there won’t be an effect upon yield. Across most of the Midwest in 2016, frost wasn’t a concern. The first killing frost occurred extremely late in many areas.
Moisture level. Some people were checking for black layer in early fall in 2016 because they suspected stalk rot would be an issue and wanted to harvest early. It became an issue in some fields, Nanda says. People often say moisture content is 30% to 32% at black layer. The Purdue guide says it can actually vary from as high as 40% to as low as 25%.
Embryo. Placental cells collapsing over one another form the black layer. The term "placental" applies because the plant is nurturing a "baby." The embryo inside the kernel makes up the bottom third or so of most kernels. Each embryo has the ability to form a tiny plant once conditions are right for germination.
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Starch component. The majority of the inside of the kernel, except for the embryo, is starch. It provides kernel weight, is the foodstuff that generates ethanol, and is the energy source when corn is ground into livestock feed. The type of starch and hardness of the starch is largely controlled by genetics. That’s why it can vary from hybrid to hybrid.
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