Specialist: Farmers facing replant still have time to stay with their intentions

Friday, May 12, 2017

COLUMBIA, Mo. -- Corn growers facing replanting decisions because of flooding and saturated soils have time to safely plant corn through the end of May and even into early June.

That is the advice from University of Missouri Extension agronomy specialist Greg Luce. He noted that growers vary in their regional situations, and, depending on their circumstances, some will decide to switch to soybeans earlier than others.

Three factors affect flooded fields most: length of flooding, temperature during flooding and drying rate.

Oxygen concentration drops rapidly in flooded fields, according to research. Oxygen depletes in 24-28 hours. Moderate water movement allows some oxygen to get to plants and causes less damage than standing water.

Young corn can survive flood conditions for about two days when temperatures are in the mid-70s or above, Luce said. They can survive four days or more when temperatures drop to 60 degrees.

Corn plants that have been flooded should show new leaves within three to five days after water recedes. Luce said soybeans can generally tolerate 48 hours underwater quite well. Flooding for four days or more significantly reduces stand, vigor and yield.

Prolonged flooding also restricts root development. This reduces the crop's ability to take up water and nutrients. This worsens root stress if a drought occurs.

Growth stage at the time of flooding also plays a key role in survivability, according to Luce. Smaller plants tend to survive underwater better than larger plants that need more oxygen, he said.

Lower air temperatures keep soil and water cooler, which actually improves the plant's chances of survival because metabolic processes slow down. However, cloudy conditions also slow drying of soil and water. Seed treatments for soybean have been beneficial, but with continued wet soils the chances of disease increase, even with treated seeds.

If cool, wet weather persists two to three weeks, poor crop stands can result.

Saturation and ponding in fields may have the same effect on seedling corn and soybean plants as flooding.

MU Extension specialists Bill Wiebold and Ray Massey offer considerations when deciding whether to replant.

Wiebold's years of research on how planting date affects yield shows that corn yields drop by 20 percent by May 26. Soybean yields drop only 2 percent when planting is delayed to May 15, but that increases to 7 percent by May 29.

He pointed out that his numbers are averages.

"No one can predict yield based upon a single year," he said.

Planting date is only one factor that determines yield, Wiebold said. Wiebold's research indicates that July and August temperatures and precipitation affect yield more than planting date.

"We've seen late-planted corn do well," Luce said. "Be patient. For now, staying with intended hybrids is the best choice."

Patience pays off for long-term soil condition also, he said. Soil conditions, rather than calendar date, should dictate when to plant.

"Don't jump into a field and compact it," he said. Compacted soil leaves less room for water, nutrients and oxygen to reach roots. Heavy farm equipment damages wet soils for years to come.

"Planting in cold, wet soils reduces seedling emergence and increases risk of soil compaction," Wiebold said. "Soil compaction limits root growth, and a healthy root system is key to withstanding hot, dry spells during summer."

Wiebold suggested that farmers review MU Extension guides when making decisions on replanting.

At times, replanting costs might exceed the value of extra yield, he said. Accurate estimates of seed costs, fuel, machinery, labor, pesticides and other costs factor into the analysis.

Cold rains right after planting cause low emergence, Wiebold said. Seeds contain 6-8 percent moisture at planting. They rehydrate with moisture from the soil. At low temperatures, the hydration process can rupture seed cell membranes. Cell contents can then leak out and become food for pathogens. This leads to seed injury or death. Damage during seed imbibition can knock out 90 percent of the stand.

The MU Extension guide "Corn and Soybean Replant Decisions" (G4091), which tells how to estimate dollar gain or loss from replanting, is available as a free PDF download at extension.missouri.edu/p/G4091.

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