CALCULATION OF THE PHOTOPERIOD LENGTH

This paper describes an algorithm for calculating the photoperiod leng th (daylength as intercepted by plants) with special emphasis on its u se in models describing plant growth and development. The ability to c alculate simply and exactly the length of the day for different locati ons is essential not only for the models describing photoperiodic effe cts on plant development but also for the simulation of the daily sum of the produced photosynthates or the calculation of the average daily temperature. Two previously published algorithms for calculation of p hotoperiod length were compared with ours, based on the system of equa tions describing movement of earth around the sun. The curve gained wh en plotting daylengths calculated by our algorithm against a particula r date is asymmetrical with respect to daylength in equinoxes, while t he curve showing the data calculated by both compared algorithms is ap parently symmetrical. The differences between our algorithm and the ot her two algorithms increase with increasing latitude: at 50 degrees N they are in the range of 6.9-13.8 min. We have also demonstrated an ef fect of location height, geographical longitude and a year on calculat ed daylength of a particular day.