Photoperiodic Alteration of Dry Matter Partitioning and Seed Yield in Soybeans1

Soybeans [Glycine max (L) Merr. ‘Ramsom’] were grown in controlled environment rooms to evaluate the effects of photoperiod during the seed‐fill period on dry motter partitioning and seed yield at maturity. Plants were grown in sand culture with a complete trient solution and at day/night temperatures of 22/18, 26/22, and 30/26 C. Initially, plants were grown under non‐inductive long‐day photoperiods. At the sixth node stage of development, the plants were moved to inductive short‐day photoperiods for 25 days until the beginning of podfill. Four plants at each temperature were then returned to the long‐day photoperiod until full pod maturity and four were retained under the short‐day period until maturity. At all temperatures, the ratio of vegetative to reproductive weight at full pod maturity was increased under the long‐day photoperiod. Pod weight was unaffected by photoperiod but seed weight and total seed yield were restricted by the long‐day photoperiod at the two higher temperatures. However, seed size and yield were greater for the long‐day photoperiod at the 22/18 C temperatures.