Abstract: Typical varieties from the main ecological regions and of different maturity stages in China were chosen for studying the post-flowering photoperiodic responses to day length in soybean (Glycine max (L.) Merr. ). The results indicated that the response to post-flowering photoperiod existed among all varieties with different maturity stages. The response was not due to of temperature effects, duration of photosynthesis or pre-flowering 15hotoperiodic after-effect Instead, it was typical photoperiodism. The response was found not only at the stages of flowering and podding but also at the stage of seed filling. Experimental results proposed that the photoperiodic demand for flowering and fruiting in soybean was a continuous process. The regulation of photoperiod on growth lasted from emergence of seedlings to maturation. There were some common basis in photoperiodic effects on both flowering induction and maturation promotion. However, the effects of photoperiodic induction had after-effect and were reversible.

Key words: Soybean, Photoperiod, Growth period