Soybean growers in Manitoba and Saskatchewan often say certain varieties are more sensitive to changes in day length, which hastens their development and progress toward maturity.


Scientists and soybean breeders take the opposite perspective, saying varieties that mature more rapidly in northern latitudes are insensitive to shortening day lengths.


Soybeans mature more quickly under hot and dry conditions, but they also respond to day length. They don’t transition from vegetative to the reproductive stage until a critical day length arrives.


“Soybean maturity genes function to delay flowering and maturity with long days,” said Elroy Cober, a soybean breeder with Agriculture Canada.


“Moving from the Midwest to Manitoba, you’re getting longer days. If you have late genes, those longer days will really delay flowering and maturity even more.”


Put another way, long days on the Prairies retard soybean development. A variety appropriate for southern Illinois might not flower in Russell, Man., until late August.


Early maturing varieties suitable for Western Canada, known as the 00 group, are less sensitive to day length, which is why they can be grown above the 49th parallel. 


“The day length question, in some of these varieties, has been bred out of soybeans,” said Horst Bohner, a soybean specialist with Ontario’s agriculture ministry. “Not bred out, but (it’s less) predominant than it was.”


Aaron Glenn, an Agriculture Canada scientist in Brandon, said growers and scientists don’t agree on the terminology.


“The language is different. I’ll say something is photoperiod sensitive if it takes those shortening days to flower,” Glenn said, while growers often describe beans that mature more quickly as day length sensitive.


“Scientifically, that’s incorrect.”


The scientific term is photoperiod insensitive, meaning beans are less dependent on shortening summer days to flower and progress toward maturity.