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Replant or not? If so, with what?

By Staff | Jul 16, 2010

Soybean fields such as this one, at the intersection of Iowa Highway 17 and County Road D56 in Hamilton County, are common sites throughout the Farm News coverage area. Growers are considering if they should replant at this late date, even if they get a reduced yield, to avoid what agronomists call fallow syndrome.

While some farmers are choosing to replant soybeans where standing water wiped out the initial crop, the biggest impact to farmers will likely be from diminished yields in areas where roots are waterlogged.

Dean Coleman, a Humboldt farmer, said about 10 percent of his soybean crop was underwater, but he was able to replant nearly 80 percent of that by July 3, just a day shy of his self-imposed deadline of replanting by the Fourth of July. “They’re up already. They’re about an inch tall,” he said, referring to the replanted beans. “With warm weather, if it maintains, we should at least get something out of those beans.”

Mark Licht, an Iowa State University Extension field agronomist for west central Iowa, said replanting soybeans in early to mid-July carries a risk, but farmers can still harvest part of a crop in replanted areas. “There is data that shows soybeans planted as late as mid-July can yield as much as 35 to 55 percent yield potential,” he said. “But there is a lot of risk replanting that late.”

In a July 1 news release, Pioneer agronomists suggested growers replant water-damaged fields to avoid “fallow syndrome,” even if some yield loss may occur. Growers who do not plant still need to till or spray fields for weed control.

The fallow syndrome is a condition that can severely limit the growth of corn and small grains. The young root systems are colonized by vesicular arbuscular mycorrhizae, which assist in nutrient uptake, primarily associated with phosphorus and zinc. The VAM population is substantially reduced when non-host crops or fallow precedes corn and small grains in rotation.

—Mark Licht ISU field agronomist

Licht said in the central Iowa counties of his territory only about 5 percent of fields were flooded, but a much higher percentage of crops are showing stress from saturated soils. “There are many more acres that are being stressed by the 20 inches of rain that fell in June. Saturated soils do make a difference. Soybeans don’t like wet feet,” he said. “Above the ground isn’t going to grow if the roots aren’t getting oxygen. This year you’re just not seeing the biomass that you usually do I think the damage has been done.”

Jim Stillman, an Emmetsburg farmer, decided not to replant the flooded areas of his fields, because there simply was too much water for the fields to dry. He estimates about 12 to 15 percent of his crop was lost. “I haven’t seen this much water in a long time,” Stillman said. “I’d say it’s the worst since about 1993.” He recorded nine inches of rain in one week in June at one of his fields and another two inches fell within the past week.

The saturated soils also make soybeans more susceptible to diseases, such as root rot and sudden death syndrome.

Even with the poor areas of fields, area farmers say much of their crop would still rate as good to excellent condition. “The good spots are really good and the rings around the wet spots are really struggling. We’ll have to wait until October to see how good the good spots are,” Coleman said.

“Those fields that are well drained or didn’t get the standing water, those crops look excellent,” Stillman said.

Contact David DeValois at dwdevalois@yahoo.com.

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