When to Terminate Corn Irrigation

  • Plants need moisture to achieve optimum plant growth and yield potential.
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  • Proper irrigation management can help to increase and stabilize crop yield potential from year to year.
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  • Irrigation should be applied until a crop reaches physiological maturity. Irrigation applied after maturity will not contribute to increased yield potential, making the application an additional expense.
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Terminating Irrigation for Corn Production

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To help achieve optimum corn yields, moisture should be available to corn plants until physiological maturity. Water requirements decrease as the plant gets closer to maturity, but maintaining proper soil moisture levels until maturity can minimize plant stress. For corn, physiological maturity occurs when the abscission layer, commonly known as the black layer, forms at the base of the corn kernel.1 Kernels will continue to accumulate seed weight until the black layer forms.

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Figure 1

Figure 1. Pictured is the milk line, the border between the dark yellow hard starch layer and the light milky dough layer.

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The maturing process begins as the hard starch layer starts to develop at the top of the kernel. The borderline separating the hard starch layer and the dough layer is referred to as the milk line (Figure 1).2 The progression of the milk line can be monitored by breaking a corn cob in half and observing the flat side of the corn kernel. The milk line separates the darker yellow hard starch layer from the dull light yellow soft dough layer.

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At complete physiological maturity (R6) the hard starch layer has reached the kernel base, the abscission layer has formed, and the plant no longer needs water for growth. At this point, kernels have attained their maximum dry weight and should have a moisture content of 28 to 35 percent. To confirm the presence of the black layer, the seed coat at the tip of the kernel can be rubbed off. The black layer should be visible at the kernel base on the opposite side of the embryo.

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Black layer formation occurs progressively from the tip of the ear (furthest from the stalk) to the base (closest to the stalk).1 To verify total black layer formation always check the youngest kernels on the ear.

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Table 1. Corn Growth Stages
R1 Silking - (silk is visible outside the husk) pollen grains fall onto the silk to fertilize the ovule
R2 Blister - (10-14 days after silking) kernels are white in color and resemble a blister in shape
R3 Milk - (18-22 days after silking) kernel is yellow on the outside with a milky white fluid inside
R4 Dough - (24-28 days after silking) liquid inside kernel thickens to a pasty consistency, cob remains white
R5 Dent - (35-42 days after silking) kernels are dented or denting and cob has turned red in color
R6 Physiological Maturity - (55-65 days after silking) kernels have reached maximum dry weight, black layer has formed where kernel attaches to the cob