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Grain fill period critical to final yieldGrain fill period critical to final yield

Corn Illustrated: A good early start has set the stage for high yields.

Dave Nanda

July 3, 2018

2 Min Read
GRAIN FILL MATTERS: Sixteen rows of plump kernels around each ear will add up to top yields. How plump and heavy kernels are depends on weather conditions during grain fill.

Early growth of corn seedlings this year was possibly the fastest we’ve ever seen. In one cornfield planted April 28, I observed seedlings with five collars on May 25 — just 28 days after planting. Sometimes it takes three weeks for seedlings to emerge.

In North America, this May was the warmest May in history since weather records have been kept. With sufficient moisture and nutrients, corn experienced fast growth. What effects could this have on grain fill and yield? Conditions were relatively dry in late May and early June, which helped root development. There were virtually no seedling diseases. Rains in mid-June certainly helped fast-growing corn plants. This fast start means the table is set for high corn yields — perhaps record-high. However, whether those yields are achieved will depend on weather during pollination and grain fill.  

For the grain fill period, it takes 50 to 60 days after pollination to reach physiological maturity, depending on relative maturity of the hybrid and temperatures. This is the payoff time for the corn plant, when the primary focus is to develop kernels fully. Corn likes cooler temperatures and sufficient water during this critical period for optimum yields. Any stresses during the grain fill period will have a negative effect on yield. Corn plants try to develop and mature as many kernels as possible.

Potential problems
If pollination of some ovules isn’t successful due to stress, it could result in incomplete kernel set. Certain insects such as Japanese beetles or corn rootworm beetles, which feed on pollen that falls on silks, can interfere in pollination and reduce kernel set. If there’s severe heat, lack of moisture or disease stress during grain fill, plants may start to cannibalize stalks and leaves to fulfill the growing needs of their progeny. Heat and drought stress can delay silk emergence and cause pollination problems. Late-emerging silks may not find any pollen left for fertilization.

As you know, the first silks to emerge come from the butt of the ear, and the last silks emerge from the tip of the ear. Kernels near the tip are more prone to be left out of pollination. That’s why you might consider planting your cornfields with hybrid pairs in alternate strips that are two to three days apart in pollen-shed dates. When pairing hybrids, try to make sure they differ in days to pollen shed.   

Plants don’t like to produce runts. If there’s stress during grain fill, plants start to abort the youngest kernels, causing tip die-back, so remaining kernels can fully develop. Physiological maturity, or black  layer, occurs at 32% to 35% grain moisture, depending on the hybrid. Stress before this period can cause kernel abortion and light test weight. If plants divert nutrients from stalks to “feed” the kernels, it can lead to premature death and susceptibility to stalk rot diseases.

Nanda is president of Agronomic Crops Consultants LLC. Email him at [email protected] or call 317-910-9876.

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