Agriculture Reference
In-Depth Information
Salinity also limits the leaf expansion
(Hsiao, 1973) and increases the incidence of
blossom end rot (BER) in the fruit (Dorais
et al
., 2001a).
In the majority of crops the minimum
average concentration of the nutrient solu-
tion required is in the order of 1.5 dS m
−1
(Sonneveld, 2003), although the production
of high quality vegetable fruits may require
EC levels as high as 2.5-3.0 dS m
−1
in the
nutrient solution (Pardossi, 2003), or even
higher (Dorais, 2001a, b, 2008) under cer-
tain conditions. The postharvest useful life
of some fruits, such as tomato or cucumber,
improves if they are cultivated at high salin-
ity (Welles
et al
., 1992), which is not the
case for pepper.
The negative effect of salinity on crops
can be mitigated by limiting the transpira-
tion rate, by means of VPD and radiation
reduction (Li
et al
., 2001), for which under
Mediterranean conditions positive effects
have been observed with shading (Lorenzo
et al
., 2003) and fogging (Montero
et al
.,
2003), although this may involve an increase
of BER in fruits like tomato.
Drain
Drain
Drain
Drain
Fig. 10.4.
Different arrangements for drainage
collection in substrate-grown crops.
is an index of the quality of the irrigation
water. The main effect of salinity in the
water or the nutrient solution is osmotic,
because the higher the salt content the higher
is the osmotic pressure of the solution.
10.4
Changes in the Management
of the Root Medium
Osmotic pressure (MPa)
= 0.33 EC (dS m
−1
) (10.1)
As the osmotic pressure increases, the water
stress increases as the water is less available
for the plants. The effects of salinity in the
production, both quantitatively and qualita-
tively, are complex as they are influenced
also by different growing conditions
(Sonneveld, 1988). Other salinity effects are
those influencing the nutrition as the
absorption of specific ions is altered, such
as the antagonism of sodium with calcium
and magnesium, or generating toxicity, in
the case of ions without osmotic relevance
(Dorais
et al
., 2001b; Sonneveld, 2003).
The salinity decreases the size of the
fruits and the fresh weight production,
because the high osmotic pressures hinder
the water supply to the fruits (Ehret and Ho,
1986), although in crops like tomato it con-
tributes to improving its organoleptic qual-
ity (Magán, 2003; Dorais
et al
., 2008).
Traditionally, the root medium fulfilled
three main functions: (i) water storage;
(ii) nutrient supply; and (iii) plant support
(Dasberg, 1999a). These three functions
have lost relevance in modern greenhouse
production systems.
The plants are not supported by the
root system, but with a complex framework
of threads and training nets. The nutrient
and water supply is regulated more and
more by the grower (and his or her comput-
ers) in substrate growing systems in accord-
ance with the changing needs of the plants.
These conditions made possible the reduc-
tion of the variability in the root medium,
relative to conventional soil cultivation, but
need continuous monitoring and control.
There is a clear trend towards the use
of water and fertilizers using closed
systems (recirculating) aimed at limiting
