Fræðaþing landbúnaðarins - Feb 2010, Page 228

| FRæðAÞING LANdBúNAðARINS 7, 2010228
more yield/m2 and fuits/m2 as plant density increased, considering that average fruit
weight was unaffected. Also in experiments from Rodriguez & Lambeth (1975)
lighting and wide spacing increased yield of tomatoes by increasing fruit size and
number. They concluded that the higher yields were due to less overlapping and
shading of leaves, better light penetration to the basal leaves, less competition for
light, water and nutrients, and higher and more efficient CO2 fixation.
The objective of this study was to test if (1) light intensity is affecting yield and outer
quality of sweet pepper, (2) this parameters are subject to modification by different
stem densities, and (3) the placement of the lights is affecting results. This study
should enable to strengthen the knowledge on the lighting regime and give vegetable
growers advice how to improve their sweet pepper production.
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
An experiment with sweet pepper ( L. cv. Ferrari) was conducted in
the experimental greenhouse of the Agricultural University of Iceland at Reykir.
Plants (two stems per plant, double rows) were transplanted at two stem densities (6
and 9 stems/m2) in four replicates. Sweet pepper was grown under highpressure
vapour sodium lamps either with only top lighting (TL, 600 W bulbs) or additional
interlighting (IL, 250 W bulbs) at four different lighting regimes:
1. TL 160 W/m2,
2. TL 120 W/m2 + IL 120 W/m2,
3. TL 240 W/m2,
4. TL 160 W/m2 + IL 120 W/m2
Light was provided for 16 / 18 hours (high / low solar irradiation), but the lamps were
automatically turned off when natural incoming illuminance was above the desired
setpoint. Temperature was kept at 2223°C / 1819°C (day / night) and ventilation
started at 24°C. Carbon dioxide was provided (800 ppm CO2 with no ventilation and
400 ppm CO2 with ventilation). Sweet pepper received standard nutrition through drip
irrigation. During the growth period green and red fruits (>50 % red) were regularly
collected and classified.
SAS Version 9.1 was used for statistical evaluations. The results were subjected to
oneway analyses of variance with the significance of the means tested with a
Tukey/ramer HSDtest at p0.05. Regression and correlation analyses were
calculated using the SAS procedure “proc reg” and “proc corr”.
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
Marketable yield of sweet pepper increased with light intensity (Fig. 1). At the lowest
light intensity the accumulated marketable yield was not influenced by stem density.
However, with higher light intensity the positive effect of a higher stem density was
becoming obvious and with the highest light intensity marketable yield was
significantly higher with 9 stems/m2 than with 6 stems/m2. This effect was developed
during the low natural light level, whereas from the middle of April (and involved
increasing solar irradiation) neither a higher stem density nor a higher light intensity
was reflected in a significant yield increment. Placement of lamps (240 W/m2 either
as top lighting alone or subdivided into top lighting and interlighting) did not affect
marketable yield (Fig. 1).