Fræðaþing landbúnaðarins - feb. 2010, Síða 227

MÁLSTOFA E – ERFðIR – AðBúNAðUR | 227
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Christina Stadler 1, Áslaug Helgadóttir 2, Magnús Á. Ágústsson 3, Monanitta
Riihimäki 4
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The extremely low natural light level is the major limiting factor for winter glasshouse
production in Iceland. Therefore, supplementary lighting is essential to maintain year
round vegetable production and this could replace imports from lower latitudes during
the winter months.
The positive influence of artificial lighting on plant growth, yield and quality of
tomatoes (Demers et al., 1998), cucumbers (Hao & Papadopoulos, 1999) and sweet
pepper (Demers & Gosselin, 1998) has been well studied. Photoperiod
recommendations for different species have been proposed and for instance for sweet
pepper photoperiods of 14 to 20 hours are recommended (Demers & Gosselin, 1998).
However, adequate guidelines for the suitable placement and light intensity are not yet
in place for sweet pepper production and need to be developed in conjunction with
plant density. Some fundamental research on these issues is reported in the literature.
It is often assumed that an increment in light intensity results in the same yield
increase. Marcelis et al. (2006) found that a 1 % light increment results in an increase
in yield of 0,71,0 % for fruit vegetables.
Traditionally, lamps are mounted above the canopy (top lighting), which entails, that
lower leaves are receiving limited light. Both old and more recent experiments (Hovi
Pekkanen & Tahvonen, 2008; Grodzinski et al., 1999; Rodriguez & Lambeth, 1975)
imply that lower leaves are also able to assimilate quite actively, suggesting that a
better utilization could be obtained by using interlighting (lamps in the row) in
addition to top lighting. Indeed, the benefits from interlighting in contrast to top
lighting alone have been confirmed with different vegetable crops. Interlighting
increased first class yield of cucumbers along with increasing fruit quality and
decreased unmarketable yield, both in weight and number (HoviPekkanen &
Tahvonen, 2008).
The influence of lighting is not considered as a separate growth factor in horticulture,
but rather as an integral part. It is assumed that at different lighting regimes an
adaption of the plant density may be useful. Modifying the plant or stem density is a
possible means to maximize light interception and yield. Based on a review of articles
of the influence of plant spacing on light interception in tomatoes, Papadopoulos &
Pararajasingham (1997) concluded that a greater fruit yield is possible in narrow
compared with wide plant spacing in greenhouse tomato, owning to increased
photosynthetic photon flux density interception, greater crop biomass and increased
availability of total assimilates for distribution to the fruits. Motsenbocker (1996)
reported that pepperoncini pepper resulted in lower biomass, lower yield/plant but