Agriculture Reference
In-Depth Information
increased light, whereas carotenoid content in fruit decreased two to threefold under
the same conditions. Similarly, Brandt et al. (
2006
) reported that the production of
lycopene was inhibited by excessive sunlight. Helyes et al. (
2006
) also found that
the lycopene content of greenhouse grown tomatoes was 40 % higher than tomatoes
grown in the open field and the more direct sunshine the fruit were exposed to, the
higher the surface temperature, leading to a lower fruit lycopene content.
Comparing light intensities between field and greenhouse structures is not easy
and as a consequence comparisons are difficult to make. Dumas et al. (
2003
) gen-
erally stated that the level of intercepted light may have affected the carotenoid
content, but interactions may also have occurred with high temperatures occurring
under protected growth conditions. Keyhaninejad et al. (
2012
) concluded that al-
though there were many differences between the field and greenhouse settings in
the above-mentioned study, which could explain the differences in fruit carotenoid
accumulation, there were very few differences between the shaded and unshaded
greenhouse settings, besides the reduced light.
Light intensity can also affect shelf life of greenhouse grown vegetables. The
postharvest shelf life of the long cucumber (
Cucumis sativus
) is generally related
to fruit greenness upon harvest. Indeed, the lower the light intensity incident on a
cucumber, the shorter its shelf life (Lin and Jolliffe
1996
; Heuvelink et al.
2006
;
Hovi-Pekkanen and Tahvonen
2008
).
Artificial Lighting
Artificial lighting mitigates the adverse influence of low and short radiation levels
and creates optimal growing conditions for protected crops. Differences in season-
al light levels can sometimes be very high where in mid-Europe the average day
length in the end of June is about 16 h, whereas in December, day length drops to
less than 8 h, while the light intensity is approximately 5 times lower.
According to Mitchell et al. (
2012
) artificial crop lighting is an energy-intensive
necessity of the greenhouse industry, particularly with increasing latitude north or
south of the equator, and can result in significant changes in seasonal photoperiod.
Greenhouse lighting requirements typically fall into these general categories: pho-
tosynthetic and photomorphogenic lighting for propagation and transplant produc-
tion; photoperiodic lighting to induce early or out-of-season flowering, and supple-
mental lighting to enhance photosynthesis for crop production, especially when
grown during light-limited periods of the year (Mitchell et al.
2012
) and where
replacement lighting that is usually used in growth rooms or chambers. However,
only supplemental assimilation lighting (SAL), which is considered the most cost-
effective form of lighting when a naturally low ambient photosynthetic daily light
source is required, or when crops are grown at a high density, will be discussed in
this section.
The main reasons for using SAL are certainly the enhanced plant growth and
crop production. Marcelis et al. (
2002
) reported yearly production increase of 55 %
