Agriculture Reference
In-Depth Information
a relatively lower peak in the blue region, Mitchell et al. (
2012
), demonstrated the
use of LEDs in emitting photon colors that match the absorbance peaks of important
plant pigments, such as the red and far-red-absorbing forms of phytochrome, or
the red and blue peaks of leaf photosynthetic action spectra. Combining the far red
and blue light rate due to LEDs not only avoids the negative effects of assimilation
lighting in greenhouses related to changes in carbohydrate metabolism, but also
contributes to a reduction of the supply of fertilizer and chemical control, due to an
aimed shortening of the vegetation period, bud/flower induction or improvement in
plant morphology.
The spectrum of assimilation lighting has recently become more important. The
use of LED lamps in a green leaved rose crop increased instantaneous crop photo-
synthesis per incident photon by up to 12 % and for a crop with reddish leaves up to
17 %, compared to HPS lamps (Paradiso et al.
2011
). Moreover, an increased red/
far red ratio on rose generally reduced plant height and increased leaf chlorophyll
content (McMahon and Kelly
1990
) and the number of flowers (Roberts et al.
1993
;
Girault et al.
2008
; Paradiso et al.
2011
).
The addition of color to plastic films or porous nets can affect various crop pro-
cesses (Shahak
2008
; Stamps
2009
). Due to a targeted application, e.g. by using
of covering films, the induction of a range of secondary metabolite accumulation
could affect the plant morphology, e.g. the plant height of transplants, as well as the
internal quality. Far red light absorbing films seem to be effective in reducing stem
elongation, and decreasing the incidence of tipburn of lettuce and blossom end-
rot of tomatoes. Recently, Patil and Moe (
2009
) reported that screening daylight
through light quality selective plastic film with a red/far-red ratio of 1.6 in combina-
tion with DIF (for more information concerning DIF, see the temperature-section in
this chapter) reduced stem, hypocotyl and internode length in the cucumber plants
by 45-50 % compared to the control film with a red/far-red ratio of 1.1, indicating
an interaction between DIF and the spectral light regime.
Changing the light intensity of different colored shade nets can affect the internal
quality of tomatoes. For example Ilić et al. (
2012
) reported higher lycopene content
in greenhouse tomatoes integrated with red shade, in comparison to field-grown
tomatoes. By contrast, shaded fruits have a lower content of β-carotene.
High Light Radiation Intensity
Two different aspects regarding light intensity include the “light compensation
point” and the “light saturation point”. The “light compensation point” is reached
when photosynthesis and respiration are in balance. The “light saturation point”, is
reached when the light intensity is increased to a point where it is no longer a factor
limiting the overall rate of photosynthesis. Extreme light intensity combined with
excessive radiation can, adversely affect plant growth and quality leading to disor-
ders in the development and appearance. Such is the case for sunscald (Fig.
10.5
).
