Make Good Soybean Management Decisions

June 22, 2008 07:00 PM
Sara Muri, Farm Journal Crops Online Editor
In the scramble to plant corn this spring, soybean planting might have been bumped down on the to-do list. As of June 15, 84% of U.S. soybeans have been planted, that compared to the five-year average of 94% planted by this date.
Palle Pedersen, assistant professor of agronomy at Iowa State University, offers the following suggestions to combating the many soybean-production problems currently facing farmers.
Beans still in the bag
While later-planted soybeans typically fair better than late-planted corn, delayed planting will still cause yield reductions. "Yields are dropping off very fast,” Pedersen says.
How to cope: He says with every day planting is delayed past May 15, yield loss increases rapidly. He says his state, for example, farmers planting soybeans in mid-June can expect:
  • 60% yield potential in Central/Northern Iowa
  • 80% yield potential in Southern Iowa
If planting is delayed until early July, farmers can expect:
  • 33 to 50% of their maximum yield
He also advises farmers to remember that delayed soybean planting equals delayed harvesting. "If Iowa soybeans are planted in early July, they will be set to harvest around Oct. 15,” he says. "And the freeze potential starts on average around Oct. 3.”
Flooded fields
Some soybean growers in Iowa, Missouri, Indiana, Ohio and other parts of the U.S. have soybeans swimming in flooded fields. Even if flood waters recede before killing the plants, Pedersen says other problems may surface.
How to cope: "It is important to remember that fields subjected to flooding also are more susceptible to nutrient deficiencies and to some root rot diseases,” Pedersen says. In addition, he notes silt deposits and other crop residue can collect on the plants and reduce photosynthesis and increase the potential of non-manageable bacterial diseases later in the growing season.
Skimpy stands
Pedersen says while farmers may be worried about small plant populations in their soybean fields, it is good to consider all the factors before replanting. He says ISU studies have shown that a final stand as low as 73,000 plants per acre has consistently yielded more than 90 percent of the optimum plant population. That population is a little bit more than two plants per foot of row in 15-inch row spacing and a little bit more than four plants per foot of row in 30-inch row spacing.
How to cope: He says it is important to wait several days (three to five) after a crop has been damaged (or has emerged) before replanting. "Injury can look very serious the day after the event but recovery may be possible.”
Weeds gone wild
"No-till fields look like pastures right now,” Pedersen says. He says weeds are coming in quick in the growing soybean fields.
How to cope: "Be aggressive,” he says "if weeds have a head-start then the yield loss from delaying planting could be even larger”
Other general soybean production management guidelines:
  • Seedbed conditions are still important when planting late. Make sure proper conditions exist before planting.
  • Plant shorter-season soybean varieties.
  • Plant a fungicide-treated seed if you are replanting a field.
  • Use a split-row planter or bean drill (don't plant wide rows using a corn planter)
 "Time is running away from us,” he says "we need to make some critical agronomic decisions.”
For More Information, visit Iowa State University's Soybean Extension and Research Program

You can e-mail Sara Muri at

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