Though it may be tempting to complete planting as soon as possible, ultra-early and early soybean planting may yield more risks than rewards, according to soybean production experts.
Before heading to the field in March or April, growers need to weigh the odds for success.
"A certain amount of time is required for seed to emerge, when soybean seed is planted in soils that are less than 50 degrees," explains Keith Whigham, Extension soybean specialist, at Iowa State University. "We have found that if we plant in March, it could be three to four weeks before soil temperatures reach 50 degrees. By then, seed may not have the viability to emerge."
Ideally, soybeans are planted the last week of April through the middle of May for optimum production, depending on geography. Typically, yield losses have been seen with early-planted (before April 15) soybeans, as well as in soybeans planted after May 15.
Weather trends, the increasing size of farm operations and some reports of yield increases with early planting have lead growers to push the envelope on soybean planting dates.
"There has not been a lot of published research dealing with very early planting dates," says Jody Gander, agronomy researcher with Pioneer Hi-Bred International, Inc., in Princeton, IL. "We initiated research in 2001 to try to quantify the potential risks or benefits associated with planting soybeans early.
"There are a few risks in planting corn early, but it is generally desirable to do so. There are a lot more risks with soybeans. Cool, wet soil conditions associated with early planting are more conducive to seedling diseases such as phytophthora root rot, pythium and fusarium, which all lead to poor emergence and growth," he says.
"When it warms up in early April, and you are tempted to plant soybeans, it is important to remember the next week it could be raining and 40 degrees," Gander cautions growers.
Early planted soybeans also appear to be more susceptible to infection from sudden death syndrome (SDS), as evidenced by widespread, severe levels of the disease, in Illinois, during the 2000 growing season. That year, as much as 65% of the soybean crop had been planted by May 15, compared to the five-year average of 20%.
"Fusarium, the organism which causes SDS, is most damaging when soil temperatures remain at 55 to 65 degrees for a long period of time," explains Jim Trybom, soybean researcher with Pioneer, in LeRoy, IL. "In 2000, soil temperatures warmed to 68 degrees May 15, but they dropped and continued to fluctuate below 65 degrees through late May.
"In 2000, the soybean seedlings and roots were exposed to the ideal 55- to 65-degree soil temperatures much longer than normal, because the crop was planted earlier than normal," Trybom adds. "The result was significant disease pressure and yield losses from SDS."
Other downsides to early planting are the potential for frost damage, which can kill soybeans that have germinated and emerged; compaction of wet soils, which impacts the crop all season long; and greater exposure to high populations of early soybean insects, since there are fewer acres in each area to attract the bugs, Whigham points out.