Fræðaþing landbúnaðarins - feb. 2010, Side 231

MÁLSTOFA E – ERFðIR – AðBúNAðUR | 231
in winter and spring. Then the environmental conditions in the greenhouse were more
easily controlled due to lower outdoor temperature, e.g., CO2 concentration could be
kept at a higher level, as the need of ventilation was lower than during the
summertime (Hovi et al., 2006). But, the difference between different lighting regimes
became smaller as the proportion of artificial light of total light energy received by
plants decreased by increasing natural light and lower use of artificial lighting (Hovi
et al., 2006), such as Näkkilä et al. (2007) reported that after midsummer, different
lighting regimes were equally productive.
In the literature, several studies can be found, where top lighting together with
interlighting increased yield compared to top lighting alone. For instance, top lighting
and interlighting (163 W/m2, 24/48 % of the lamps mounted between the rows at 1,30
m height) increased the annual yield of cucumbers compared to top lighting alone
(170 W/m2) in weight mainly due to higher fruit weight, as there was no significant
effect on the total yield in number (HoviPekkanen & Tahvonen, 2008). But, also in
sweet pepper, interlighting (50 % of top lamps and 50 % of lamps mounted vertically
between the single plant rows) was shown to enhance productivity, increasing both
the total (23 %) and first class (15 %) fruit yield of sweet pepper and number (18 %)
(Hovi et al., 2006). Beside that, improved interlighting (compared to top lighting) the
energy use efficiency (HoviPekkanen & Tahvonen, 2008). Gunnlaugsson &
Adalsteinsson (2006) observed a variety dependent yield advantage effect of
interlighthing: The amount of interlighting (22/45 %, 250 W bulb) did not affect the
tomato yield of the variety “Geysir” whereas “Espero” gave the highest yield when
illuminated with 45 % interlights and the lowest yield when only top lights (238
W/m2, 600 W bulb) were used. This effect may also be the reason for the not
advantageous effect of interlights in the present study.
It was observed that interlighting reduced outer quality of sweet pepper due to a
higher amount of fruits with blossom end rot besides damages of fruits through
burning by interlighting. Also Hovi et al. (2006) reported that blossom end rot was
slightly increased in interlighting and increased in each treatment with increasing
natural light and temperature during the summertime. In contrast, interlighting in
cucumbers decreased the unmarketable yield in weight and number compared to top
lighting, increased chlorophyll concentration of fruit skin in each stand and visually
greener fruits and slightly extended the postharvest shelf life of fruits (Hovi
Pekkanen & Tahvonen, 2008). This may indicate that some vegetable crops are more
sensitive to interlighting than others and interlighting may have in crops or varieties
an advantageous effect on yield as well as on quality.
Incorporating a higher light intensity means also that an adaption of the stem density
may be useful, like it was shown in this study. Also, for example Heuvelink et al.
(2006) reported that with supplemental lighting an increase in planting density of
cucumbers of 1% improved yield with 0,5% without a reduction of quality. However,
a higher light intensity is not converted as efficient as a lower light intensity into
yield. Therefore, not only the yield but also the profit margin seems to be necessary to
be examined more closely.