Direct solar radiation penetration into row crop canopies in a lean-to greenhouse

Abstract

Experiments were conducted using model row crop canopies inside a model lean-to greenhouse (ratio 1 : 15) under artificial light to investigate the relations between row orientations and amount of direct solar radiation received by the canopy leaves. The model leaves were round in shape, horizontal in leaf inclination. The difference between the azimuthal directions of every two vertically neighbouring leaves was 90°. The east–west (E–W) and north–south (N–S) row canopies consist of 110 (5 rows × 22 plants/row) and 98 (14 rows × 7 plants/row) plants, respectively, and both gave a leaf area index of 1.16. Solar cells, each with a detecting area of 1.0 cm × 1.0 cm, were set on the surface of the upper 10 leaves of each measuring plant to detect the solar radiation reaching it. At 35°N, E–W row canopy showed higher normalized daily canopy irradiance than that of N–S row canopy during the winter and early spring months, while the results became the opposite for the rest of the year. At 45 and 55°N, on the other hand, N–S row canopy showed higher normalized daily canopy irradiance than E–W row canopy throughout the year. Moreover, magnitude of the differences in normalized daily canopy irradiance between row orientations was bigger in summer and late spring months than in winter and early spring months. Further analyses showed that the differences between E–W and N–S row canopies mentioned above were mainly due to the differences of normalized canopy irradiance during almost the whole day in spring and summer, and the differences in the integral value over the day of normalized canopy irradiance in winter.