Temperature Control of Time Intervals Between Vegetative and Reproductive Events in Soybeans1

An attempt was made to develop general relationships quantitatively describing the effect of temperature on growth and development of a soybean Glycine max (L.) Merrill shoot. The time required for emergence and expansion of cotyledons and the appearance of the first pair of unifoliolates and of subsequent successive trifoliolate leaves on the main shoot was measured in controlled environments in a phytotron. For plants in greenhouses in midsummer, degree‐days per trifoliolate on the main shoot was fairly constant between 12 and 30 C. In the 30 C greenhouse the rate of trifoliolate emergence was much less in late fall than in early spring, suggesting that photosynthate supply was limiting in late fall. Increasing photosynthate supply by enriching the CO 2 level around the plants in growth cabinets did not greatly affect the rate of trifoliolate emergence. This kind of data may permit the logical development of programs that simulate soybean growth.