Agriculture Reference
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tion of photosynthesis at chloroplast level, which is partly associated with reduced
chlorophyll concentration, and alterations in carbon allocation and utilization aimed
at the adaptation of plants to a saline environment. Grieve (
2010
) reported that
some plants can adjust osmotically within hours, where cell volumes and turgor
are restored, but irreversible damage has already been done. Cell elongation and
cell division are reduced, and, as a result, shoot growth decreases. Roots are also
reduced in length and mass. Moderate salinity levels, which are crop depended,
usually restrict growth without any overt injury symptoms and the plants appear
normal, but stunted.
Even in SCSs, high salinity levels can be detrimental to plant growth. Rouphael
et al. (
2008
) investigated the growth and quality of zonal geranium (
Pelargonium
×
hortorum
'Real Mintaka') in closed soilless systems, in order to evaluate the effects
of the irrigation system (drip and sub-irrigation) and nutrient solution concentration
under various conditions of radiation and temperature. The authors found that the
ECs during the spring season at the end of the growing cycle was two-fold higher
than that observed in the winter season, due to higher solar radiation and higher air
temperature, and was almost double in a full than in a half strength nutrient solu-
tion. Consequently, plant growth with sub-irrigation using a full strength nutrient
solution during spring season resulted in lower shoot biomass, growth and qual-
ity index than those grown using drip-irrigation. Similar results were obtained by
Santamaria et al. (
2003
) with cherry tomatoes and Rouphael and Colla (
2005
) with
zucchini squash. The increase of EC in the upper layer of the substrate reduced the
fruit yield of both crops cultivated in sub-irrigated systems. In other trials, however
closed-cycle sub-irrigation systems were successful for tomato production using
saline water (Incrocci et al.
2006
; Montesano et al.
2010
). According to Incrocci
et al. (
2006
), the process of fast water salinization made it necessary to flush out
the nutrient solution in six different occasions in a closed-loop aggregate culture
using the drip irrigation system, with a subsequent loss of water and fertilizers. On
the contrary, in sub-irrigation culture, the upward water movement in the substrate,
coupled with selective mineral uptake by the roots, caused salinity build-up and
sodium accumulation in the upper region of the substrate. Here the authors conclude
that sub-irrigation conducted with saline water can be a tool to reduce water con-
sumption and nutrient runoff in closed-loop substrate culture of tomatoes and retain
fruit yield and quality of tomatoes.
Improvement on Product Quality Due to a Moderate Salinity Stress
According to Grieve (
2010
), moderate salinity can improve the quality of vegeta-
bles, due to changes in two classes of phytochemicals: compatible osmolytes and
antioxidants. Many investigations have shown that using solutions with moderate
electrical conductivity, achieved by adding sodium chloride or nutrients, the first
one being more common due to economic concerns, can improve the tomato fruit
quality, in terms of organic acidity and total soluble solids (Mizrahi and Paster-
nak
1985
; Sonneveld and Welles
1988
; Adams and Ho
1989
). These results are
