The final stages of yield determination occurs during the grain fill period. The grain fill period begins with the initiation of kernel development following pollination and ends approximately 60 days later when the kernels are physiologically mature.
A stress-free grain fill period can result in record yields (e.g., 1992), while severe stress during grain fill can kernel abortionor lightweight grain. The serious pupil of corn will want to track the progress of grain fill in fields, so here is a crib-sheet on kernel development stages.
About 10 to 14 days after silking, the developing kernels are whitish 'blisters' on the cob and contain abundant clear fluid. Some starch is beginning to accumulate in the endosperm. The ear silks are mostly brown and drying rapidly. The radicle root, coleoptile, and first embryonic leaf have formed in the embryo by the blister stage. Severe stress can most easily abort kernels at pre- blister and blister stages. Kernel moisture content is approximately 85 percent.
About 18 to 22 days after silking, the kernels are mostly yellow and contain 'milky' white fluid. The milk stage of development is the infamous 'roasting ear' stage, that stage where you will find die-hard corn specialists out standing in their field nibbling on these delectable morsels. Starch continues to accumulate in the endosperm. Endosperm cell division is nearly complete and continued growth is mostly due to cell expansion and starch accumulation. Severe stress can still abort kernels, although not as easily as at the blister stage. Kernel moisture content is approximately 80 percent.
About 24 to 28 days after silking, the kernel's milky inner fluid is changing to a 'doughy' consistency as starch accumulation continues in the endosperm. The shelled cob is now light red or pink. By dough stage, four embryonic leaves have formed and about 1/2 of the mature kernel dry weight is now in place. Kernel abortion is much less likely once kernels have reached early dough stage, but severe stress can continue to affect eventual yield reducing kernel weight. Kernel moisture content is approximately 70 percent.
About 35 to 42 days after silking, all or nearly all of the kernels are denting near their crowns. The fifth (and last) embryonic leaf and lateral seminal roots form just prior to the dent stage. Severe stress can continue to limit kernel dry weight accumulation. A distinct horizontal line appears near the dent end of the kernel and slowly progresses to the tip end of the kernel over the next 3 weeks or so. This line is called the 'milk line' and marks the boundary between the liquid (milky) and solid (starchy) areas of the maturing kernels. Severe stress can continue to limit kernel dry weight accumulation. Kernel moisture content at the beginning of the dent stage is approximately 55 percent.
About 55 to 65 days after silking, kernel dry weight usually reaches its maximum and kernels are said to be physiologically mature and safe from frost. Physiological maturity occurs shortly after the kernel milk line disappears and just before the kernel black layer forms at the tip of the kernels. Severe stress after physiological maturity occurs has little effect on grain yield, unless the integrity of the stalk or ear is compromised (e.g., ECB damage or stalk rots). Kernel moisture content at physiological maturity averages 30 percent, but can vary from 25 to 40 percent grain moisture.
While not strictly a stage of grain development, harvest maturity is often defined as that grain moisture content where harvest can occur with minimal kernel damage and mechanical harvest loss. Harvest maturity is usually considered to be near 25 percent grain moisture.
Return to The Corn Growers Guidebook , a WWW resource for corn management systems in Indiana and the eastern CornBelt.
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