How is corn really doing in the middle of a drought?

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Minimal rain has scattered itself across the Corn Belt in the past month, and many farms are reporting only half of the normal amount of rainfall that could be expected so far in the growing season. With USDA crop progress reports again scheduled for Monday afternoon, most will show the majority of topsoil moisture in short to very short categories.  With a growing drought area, how is the corn crop really faring?

The quote of the week came from Purdue University’s corn specialist Bob Nielsen, and it was not about tulips or Tiny Tim, when he said, “We’re tip-toeing on the edge of something serious.” In comments quoted by the Purdue news service, Neilsen said, “Right now, it’s wait-and-see; it could go either way.” Discussing the drought impact on Indiana corn, Nielsen said, “Several areas of the state are under severe stress and, early in the growing season, there’s already concern about the impact it will have on yield. If we begin to get rain, the corn crop won’t recover completely, but it will be better than we thought.” But he said a return to hotter weather tips the scales.

Neilsen’s counterpart at the University of Illinois, Emerson Nafziger said the corn is growing, but is mediocre at best, particularly with the deficit of soil moisture. Nafziger says that means a reduction in photosynthetic activity and a reduction in dry matter production. As the plant grows, and leaf area expands, so does the opportunity for more moisture loss. Unfortunately for the plant, he says there may be 2-3 inches of water per foot of soil, but if the dry topsoil curtailed root development, the plant could not tap the water resources underground. Nafziger says that is the problem of rootless or “floppy” corn, which cannot stand up due to lack of brace roots.

But if there is minimal water in the soil, and roots have died back for lack of moisture, how can the corn plant be increasing in size?  Nafziger says that is happening at night, but at a cost, since he says the current dry period will result in reduced size of crops and grain, with a direct impact on yield.  He says plants grow with water causing expansion of cells at night when plants are not losing water through the transpiration process.  He says true growth occurs in daytime from photosynthesis, and is an increase in the plant’s dry weight, which includes grain. 

While the plant has been adding leaves, it has also been forming the tassel and shoot structure within the stalk, which has not been a friendly location for a lack of water. Ohio State University agronomist Peter Thomison says, “As early as the V4/V5 stage, ear shoot initiation is completed and the tassel is initiated on the top of the growing point. During the rapid phase of corn vegetative growth (which generally starts by V7), ear yield components are being determined. Kernel row numbers per ear are generally established by about V7. However, unlike kernel rows per ear, kernels per row can be strongly influenced by environmental conditions. Severe drought stress during the two weeks prior to pollination can reduce kernels per row and cut yield.”

Summary
With the dry soil there is no surprise that corn plants will be impacted negatively. Plants are growing larger, but only because cells expand at night when there is no transpiration. However, the plant is not accumulating dry matter since the lack of water impedes photosynthesis during the day time. The tassel and ear shoots are forming, but within a stalk that is lacking water.  The crop in many fields is on the edge of serious damage, and may be in trouble without some relief in the next two weeks.

Source: FarmGate blog



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