2018 ASHS Annual Conference

Soybean (Glycine max L.) is a short-day plant, requiring a controlled photoperiod to produce seeds in a greenhouse environment year-round. The purpose of this experiment was to define the duration (number of weeks) of short-days soybean plants need to stimulate reproductive growth in order to not revert back to vegetative growth after exposure to long-days(16 h). Two determinate soybean varieties, within the same maturity group, were sown into 32-cell flats filled with a peat-based soilless substrate, and placed in a greenhouse with a 16-h photoperiod. After 3 weeks, plants were transplanted into 22.8-cm-diameter plastic pots, and transferred to a photoperiod controlled greenhouse. The day/night temperature set points were 26.6/21.1 °C. The soybean plants were then subjected to a 14-h photoperiod for 2 weeks. Upon completion of the 2nd 14-hour week, the 7 treatments of the experiment began. Plants were treated with 1, 2, 3, 4, 5, 6, or 7 weeks of a 12-h photoperiod after which plants were returned to 16-h photoperiod. A control group received a 12-h photoperiod beginning with other treatments but remained at that photoperiod for the remainder of the experiment. Number of nodes with pods, cycle time, and yield were recorded. Both varieties and all treatments showed just as good or better yield, cycle time and number of nodes with pods compared to the control. Based on the data from this experiment, photoperiod control past one week at 12-hours does not have any negative impacts on yield, cycle time or number of nodes with pods for the two varieties tested.