INSTANTANEOUS AND INTEGRATED LIGHT MEASUREMENTS WITHIN AN APPLE CANOPY

in HortScience

Integrative measurements of photosynthetically active radiation (PAR) were made at 30 `Delicious' canopy positions throughout the season to characterize the canopy light environment. Instantaneous measurements (IM) of PAR were made at the same positions with a quantum sensor on clear and overcast days and correlated with integrated seasonal PAR. Hourly (1100, 1200, 1300, and 1400 hrs) IM made on clear days were influenced b sunflecks and had variable relationships with integrated values (R2 = 0.52-0.90). This was improved by using the average of the four IM measured during the day (R2 = 0.92). Hourly IM on overcast days were consistent and highly correlated to integrated values (R2 = 0.97). IM from overcast days were reliable predictors of seasonal PAR and could be used to characterize the canopy light environment.

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