Agricultural and Forest Meteorology 100 2000 243–253
Direct solar radiation penetration into row crop canopies in a lean-to greenhouse
S. Li
∗
, K. Kurata, T. Takakura
Department of Biological and Environmental Engineering, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan Accepted 1 November 1997
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 plantsrow and 98 14 rows × 7 plantsrow 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.
©2000 Elsevier Science B.V. All rights reserved.
Keywords: Row crop canopy; Direct solar radiation; Lean-to greenhouse; Scale-model experiment
1. Introduction
In greenhouse production, effective utilization of the transmitted solar radiation by the crop canopies
inside is an important research subject. Generally, the quantity of direct solar radiation intercepted by a row
canopy mainly depends on its row orientation, plant- ing density and geometric structure, provided that
the amount of transmitted solar radiation is a con-
∗
Corresponding author. Present address: Department of Horti- culture, Clemson University, Clemson, SC 29634-0375, USA.
stant. As for the row orientation, in recent years more practical cases of north–south N–S row canopies
could be found in vegetable productions inside the lean-to greenhouses, the predominant greenhouse de-
sign used in central and northern China regions of about 35–45
◦
N, though this is the case based on no scientific reasoning and no experiment or analysis has
been made so far. Many analyses on the effects of canopy structures
on solar radiation interception by row canopy Allen, 1974; Iwakiri and Inayama, 1974; Lang and Shell,
1976; Mann et al., 1980; Mutsaers, 1980; Nederhoff,
0168-192300 – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 9 2 3 9 9 0 0 0 4 4 - 1
244 S. Li et al. Agricultural and Forest Meteorology 100 2000 243–253
1984; Myneni et al., 1986; Whitfield, 1986; Goudri- aan, 1988; Kurata et al., 1988; Gijzen and Goudriaan,
1989; Yang et al., 1990a, b have been done in the past. However, only a few studies dealing with the effect of
row orientation on solar radiation interception by the row canopy can be found among them. Allen 1974
conducted a study on direct-beam radiation penetra- tion into a wide-row crop canopy the dimensions of
the canopy were: width of inter-row W
ir
= 60 cm, row height H
r
= 80 cm, row width W
r
= 40 cm of field sorghum and concluded that there were 37
and 44 daily interceptions for east–west E–W and north–south N–S row orientations, respectively 17
August, 40
◦
N. Iwakiri and Inayama 1974 made nu- merical calculations on the characteristics of direct so-
lar radiation penetration into cucumber row canopies the dimensions of the canopy were: W
ir
= 100 cm,
H
r
= 150 cm, W
r
= 80 cm grown in a plastic green-
house based on the understanding of the canopy geometric structures through experimental measure-
ments. Their results showed that E–W row canopy gave a higher percent sunlit leaf area FlFt: where
Ft indicates leaf area index LAI and Fl the sunlit LAI on the winter solstice and the vernal equinox,
but a lower value on the summer solstice than the N–S row canopy 35
◦
N. Mutsaers 1980 carried out computer simulations to investigate the effect of row
orientation, season and latitude on light absorption by row crop canopies the dimensions of the canopy
were: W
ir
= 50 cm, H
r
= 100 cm, W
r
= 50 cm. His re-
sults showed that at latitudes of 35–55
◦
N, daily direct light absorption is highest with N–S row orientation
during the summer months and with E–W orientation for the rest of the year. Kurata et al. 1988 utilized
fisheye photography to analyse the effect of row ori- entation on the direct solar radiation interception by
tomato row canopies and obtained results similar to those of Iwakiri and Inayama 1974. For example,
in winter E–W orientation gave a higher value of daily canopy absorptance ratio of daily integral of
intercepted direct solar radiation to daily integral of incident direct solar radiation than N–S orientation,
but in summer E–W orientation showed lower daily canopy absorptance than N–S orientation 35
◦
N. However, these analyses seem to have diffi-
culty in giving satisfactory explanations to the above-mentioned practical case being conducted in
the lean-to greenhouses in China. Furthermore, almost all the research on solar radiation penetration into crop
canopies conducted so far was based on mathematical models, and no report was found in the literature on
direct measurement of the solar radiation reaching the leaves’ surfaces of the row crops. This is mainly
because of the very complicated geometric structures of the crop canopies, which makes it almost impos-
sible to conduct complete measurements inside them. Moreover, in respect to solar radiation environments
of a row crop canopy cultivated in greenhouses, no work dealing with both the effects of row orienta-
tion and the greenhouse structure has been reported. The above-mentioned analyses made by Iwakiri and
Inayama 1974 and Kurata et al. 1988 came from research on greenhouse row canopies, but the effects
of greenhouse structures were not included in their results.
In the present study, model row crop canopies, for which some simplifications on the geometric struc-
tural parameters were made, were put into a model greenhouse, and experimental measurements were
conducted under artificial direct solar radiation. The purpose of this study was to investigate the effect of
row orientation on direct solar radiation interception by the row canopies.
2. Materials and methods
