000			02024nab a22003497a 4500
001			39649
003			CO-PlCIA
005			20130510185006.0
040			_aCO-PlCIA _cCO-PlCIA
041			_aeng
245			_aEffective day lengths for the study of photoperiod sensitive reactions in plants
100			_aFrancis, Charles Andrew
008			120511t1970 000 0seng d
300			_a62(6):790-792
520			_aThe number of hours with a light intensity above the critical level for photoperiod sensitive reactions in plants is greater than the number of sunglight hours. In temperate latitudes, dark periods calculated from time of sunset to sunrise are nearly 1 hour longer than the effective dark period with an intensity less than 1 ft.-c.; conversely, the effective photoperiod is longer by 1 hour. The length of the twilight period was used to calculate the number of "photoperiod effective" hours above critical intensities of 10, 5, 2, and 1 ft.-c. (108, 54, 22, and 11 lux). These photoperiodic day lengths are presented for latitudes from 70 degrees N to 60 degrees S and all months of the year. Heavy cloud cover reduces the effective photoperiod, while scattered high clouds may reflect enough light from the sun below the horizon to lengthen the day slightly. These physical day lengths may be used to predic plant response for different planting dates in a given location when critical intensities of light and critical photoperiods which influence reactions in each crop sciences are known _9eng
650			_aPhotoperiodicity _9eng
650			_aDaylight _9eng
650			_aCrops _9eng
650			_aAdaptation _9eng
650			_aFotoperiodismo _9spa
650			_aLuz del día _9spa
650			_aCultivos _9spa
650			_aAdaptación _9spa
653			_aThompson _9spa
653			_aCIAT Autor _9spa
653			_aRJ _9spa
773			_tAgronomy Journal (USA) _d1970
998			_aCATAL
998			_aBICIAT
653			_aArticles in Refereed Journals _9eng
942			_2lcc _cJA
999			_c88632 _d88632