Manhattan, Kansas, USA
September 20, 2011
Pod set in soybeans has been running later than the 5-year average across Kansas this year, in part because of the extremely high temperatures this summer during much of the time that beans were trying to set pods, said Kraig Roozeboom, K-State Research and Extension crop production specialist.
This may have an effect on yields, depending on how long pod set was delayed and when the first freeze occurs this fall, he said.
“Not only have the high temperatures and drought delayed pod set, these conditions have also slowed seed fill on beans,” he said. “Where pod set was delayed until mid-September, yields will probably be severely reduced. If pod set occurred in late August, soybean fill and yield also will likely be reduced for most locations.”
The reason for the lower yields is that seed size will likely be reduced where pod set was delayed, he explained.
“It typically takes about 60 days from flowering to maturity to fill soybean seed of a typical size – about 2,500 seeds per pound -- with average temperatures and rainfall. If soybeans have fewer days of seed fill than that, seed size will be reduced,” he said.
Producers can estimate for themselves whether their soybeans might have less time than needed for normal seed fill, he said.
“Take the average date of the first fall freeze, count back 60 days from that date, and see if your soybeans had set all or most of their pods by that date,” he said.
“For example, the average date of the first fall freeze in Chanute is October 24. If soybeans had started pod set by August 25, that would give them about 60 days of seed fill – assuming that the first freeze occurs at the normal time – and the potential for average seed size assuming average filling conditions. If pod set began any later than that, there’s the possibility for a shortened seed fill period, reduced seed size and lower yields,” Roozeboom said.
If the beans have been subjected to heat and extremely dry conditions, beans may not be filling at a normal rate, further reducing yields, he added.
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