Comparison of relative illuminance, relative photosynthetic photon flux and relative cumulative amount of global solar radiation in apple tree canopy

Abstract

Relative light intensities in an apple (Malus domestice Borkh.) tree canopy were determined by measuring light quantity:photometrically (illuminance, lx), radiometrically (radiation, W · m-2), and in quantum terms (photosynthetic photon flux, μ mol · m-2 · s-1). There was a strong positive correlation between relative illuminance and relative photosynthetic photon flux, measured on an overcast day. Relative photosynthetic photon flux was, however, 6.0% higher than relative illuminance. A strong correlation was also found between relative illuminance and relative cumulative photosynthetic photon for one day; the latter was higher by 6.7% on an overcast day and 6.8% on a clear day. There was a strong positive correlation between the relative cumulative photosynthetic photon and the relative cumulative amount of global solar radiation for one day, while that of relative cumulative photosynthetic photon was 11% lower than relative cumulative amount of global solar radiation.