It is difficult to explain the real reasons about unstable yield of soybean in a lean year in south China but some clues have been indicated in this serial experiments.(1)The different soybeans has its own respective short-light criticals and limits and characteristics values of the basic vegetative period.These characteristics would be reflected in their growth and development in other circumstance.(2) The effect of light and temperature to the growth period presented a mutual promotion and mutual restrai...