The transmission of global and photosynthetically active radiation within a dwarf apple orchard

Abstract

SUCKLING, P. W., J. A. DAVIES, and J. T. A. PROCTOR. 1975. The transmission of global and photosynthetically active radiation withinadwarfappleorchard. Can. J. Bot. 53: 1428-1441. Measurements of incoming global radiation, K J , beneath a dwarf apple orchard canopy were made with a traversing sensor and a randomly located set of 10 stationary sensors. The location of the latter was changed once during the period of the experiment. On a daily basis, satisfactory agreement between the two sets of measurements was attained only for the second network location.Above-canopy and track measurements were used to calculate diurnal and daily values of canopy transmissivity, absorptivity, and reflectivity. Average values for the whole period were 0.53,0.28, and 0.19. Analogous coefficients were obtained for photosynthetically active radiation (PAR). Extracanopy values of PAR were evaluated from PAR = 0.49 KJ on 'bright' days (days with cloud cover less than 6 / , , ) and PAR = 0.5 KJ for cloudy days. These relationships were obtained by regression from sample measurements of PAR and KJ. Average PAR transmissivity, absorptivity, and reflectivity were evaluated as0.42,0.51, and 0.07. SUCKLING, P. W., J. A. DAVIES et J. T. A. PROCTOR. 1975. The transmission of global and photosynthetically active radiation within adwarfapple orchard. Can. J. Bot. 53: 1428-1441. Les auteurs ont mesurt I'irradiation incidente globale, K J , sous le couvert d'un verger de pommiers nains, I'aide d'une cellule photosensible se d t p l a~a n t a travers le verger et d'une batterie de 10 cellules stationnaires distributes au hasard. La position de ces dernikres a t t i changte une fois au cours de la ptriode d'observations. Sur une base quotidienne, ce n'est que dans cette deuxikme position que les rtsultats obtenus avec les deux types de cellules ttaient suffisamment concordants. Les mesures obtenues au-dessus du couvert et celles obtenues avec le senceur mobile ont kt6 utilistes pour calculer les valeurs diurnes et quotidiennes de la transmittance, de I'absorbance et de la rtflectance du couvert. Des valeurs moyennes de 0.53,0.28 et 0.19 ont CtC obtenues pour toute la ptriode d'observation. Des coefficients analogues ont e t t obtenus pour la radiation active sur la photosynthkse (PAR). Les valeurs de PAR ii I'exttrieur du couvert ont kt6 CvaluCes a PAR = 0.49 KJ pour les jours ensoleillts (moins de 6jours sur 10 Ctaient couverts), et a PAR = 0.5 KJ pour les jours couverts. Ces relations ont Ctt obtenues par rtgression a partir d'tchantillons de mesures de PAR et KJ.. En moyenne, la transmittance, I'absorbance et la rtflectance de PAR etaient de 0.42,0.51 et 0.07.[Traduit par le journal]

Atmospheric effects on insolation in the Brazilian Amazon: Observed modification of solar radiation by clouds and smoke and derived single scattering albedo of fire aerosols

“…The record of scientific literature based on empirical results is of varied opinion on this matter. Several studies have suggested a moderate or large increase in PAR fraction under cloudy conditions [ Blackburn and Proctor , 1983; Rodskjer , 1983; Rao , 1984], while other studies indicate small or negligible increases of 2 percent or less [ Suckling et al , 1975; Papaioannou et al , 1993, 1996].…”

The Effect of Supplemental HPS Lighting during Propagation on Rooting and Quality of ‘White Marble’ Cut Chrysanthemums1

“…Ambient radiation was measured in langleys/day at the Research Station in Elora, Ontario using an Eppley pyranometer. Ambient PAR within the greenhouse was calculated assuming that 50% of the radiation measured was in the visible range (12) and that 60% of this was transmitted into the greenhouse (5). To facilitate comparisons with the levels of HPS irradiance the langleys/day values were also converted to MJ m 2 day'1.…”

The Carbon Budget of a Young Apple Tree1

“…Since radiation interception by leaves on shoots is dependent on both canopy architecture and the radiation regime complete and detailed analysis would be extremely complex. Much of the information required for such analysis is lacking for apple trees but some progress has recently been made (5,6,12,17).…”