Photoperiodicity is the physiological reaction of organisms to the length of day or night. The total amount of energy is unimportant as long as it exceeds some low minimum level required to trigger changes in phytochrome. Response to photoperiodic stimuli include flowering, tuber and bulb formation, bud dormancy, seed germination etc. Since the relationship between the daily succession of light and dark periods frequently influences flowering and fructification of plant species, photoperiod appears as a major contributing factor in limiting areal plant species and associations. Knowing the variation of the daily light period duration and requirements of various plants in different growing phases according to the day light is useful in agricultural practice in order to determine the period of plant cultivation, crop rotation and duration of lighting in protected areas (greenhouses, solariums) in the case of using additional sources of illumination. Establishing successive vegetable cultivation and instalments will be both depending on their requirements according to day length and on the purpose for which plants (leaves, underground organs, inflorescences, etc.) are being cultivated. Since the change in the duration of daily light depends on the location this paper presents a calculation method in order to determine the period of the year with a certain minimum amount of daylight duration depending on the latitude value of the location expressed in degrees and minutes.

photoperiodicity; duration of daily light; location in degrees

Presentation: oral