Agriculture Reference
In-Depth Information
greenhouses (Baille and Tchamitchian,
1993). Increasing the relative fraction of dif-
fuse radiation in greenhouses contributes to
higher radiation uniformity within the
greenhouse (Kurata, 1992) and to yield
increase, due to higher radiation efficiency
(Baille, 1999). The increasing use of highly
diffusing cover materials (mainly PE films)
in the Mediterranean area contributes to
less direct solar radiation inside the green-
house, and thus more diffuse radiation
(Cabrera
et al
., 2009); this increase in dif-
fuse radiation usually results in higher yield
(Magán
et al.
, 2011).
Crops such as fruit vegetables with a
high plant canopy utilize diffuse radiation
better than direct radiation, as diffuse radi-
ation penetrates the middle and lower lay-
ers of a high-canopy crop and results in a
better horizontal radiation distribution in
the greenhouse (Hemming
et al
., 2008). For
this reason, as stated by Cabrera
et al
. (2009),
starting with the pioneering work of Deltour
and Nissen (1970), laboratory studies aimed
at characterizing the diffusive properties of
greenhouse cladding materials have become
of paramount interest (Pearson
et al
., 1995;
Wang and Deltour, 1999; Montero
et al
.,
2001; Pollet
et al
., 2005).
We may distinguish between external
quality, which includes those visible attributes
(shape, colour) and internal quality (flavour,
shelf life) which cannot be evaluated at a
glance (Kader, 2000). Several aspects of qual-
ity are measurable (analytical quality) whereas
some others are subjective (emotional qual-
ity). This emotional quality is, sometimes,
related to the mode of production, such as
integrated or organic production (Vonk-
Noordegraaf and Welles, 1995).
Sometimes, in tomato, a certain decrease
in production may be compensated for by an
increase in the organoleptic quality of the
product (Adams and Ho, 1995; Schnitzler
and Gruda, 2003), maintaining or even
increasing the economic return.
For the consumer, the appearance is the
most important qualitative criterion when
buying (at least, until the product is con-
sumed), so the size, the shape and the uni-
formity, the colour and the absence of visible
defects are the aspects most usually consid-
ered as qualitative elements when choosing
the product (Urban, 1997a). Although fre-
quently their contribution to the decision-
making power in the distribution chain is
limited, at least in the short term, in relation
to other agents of the chain, such as the pur-
chasing managers.
For more information about quality see
Chapters 15 and 16.
6.10
Production Quality
6.10.1
Introduction
6.10.2
Effects of climate factors
on quality
Besides the fresh weight of the harvestable
products, their quality determines the yield
of greenhouse vegetables. Quality is a combi-
nation of attributes, properties or character-
istics which give each product a value,
depending on its use (Kader, 2000). Quality
may be defined as the group of characteris-
tics by which the product and the produc-
tion mode satisfy the demand of the buyers,
traders and distributors, and the expecta-
tions of the consumers (Vonk-Noordegraaf
and Welles, 1995). The quality criteria, obvi-
ously, are not the same throughout the distri-
bution chain, from the grower to the
consumer, varying depending on the product
and the way it is consumed (Kader, 2000).
A high rate of photosynthesis affects the
production of sugars and acids, which are
very important compounds in the flavour of
fruit vegetables (Vonk-Noordegraaf and
Welles, 1995). High radiation favours the
sugar content and decreases the acid con-
tent (Janse, 1984) while it limits the harm-
ful
accumulation
of
nitrates
in
leafy
vegetables.
The external quality is also affected by
the light, at first through photosynthesis,
since with higher photosynthesis levels
(under proper conditions of competition
between organs) larger fruit sizes are
expected (Cockshull
et al.
, 1992). In addition,
