Flowering in soybean is initiated by short daylength. There are several investigations exploring the genetic basis of the photoperiodic response in crop plants. However, such studies in soybean are quite limited.
"Research notes: Inheritance of time of flowering under short-day conditions,"
Soybean Genetics Newsletter: Vol. 5
, Article 29.
Available at: http://lib.dr.iastate.edu/soybeangenetics/vol5/iss1/29