Agriculture Reference
In-Depth Information
improve the final fruit number or the yield of these crops, but reduced vegetative
growth. Continuous water stress throughout the season can also diminish leaf area,
fresh and dry weight, but did not hasten ripening, necessary for mechanical harvest,
but rather delayed fruit maturation in relation to other treatments. Water deficit, ei-
ther sustained or applied at the fruit ripening phase, was detrimental to commercial
yields of pepper (González-Dugo
2007
). Patanè et al. (
2011
) also reported that full
irrigation is required to maximize marketable yield in processing tomatoes cultivat-
ed in semi-arid climate conditions. The authors stated however that an adoption of
deficit irrigation strategies could be considered, especially in areas such as those of
the Mediterranean basin, where water resources are increasingly scarce. Indeed, be-
sides the conspicuous irrigation water savings (up to 48 %), full irrigation resulted
in a yield reduction proportionally less than the water deficit (Patanè et al.
2011
).
Oxygen in the Root Environment
Optimal root development requires a sufficient oxygen supply. In soilless cultures,
oxygen deficiency in the root environment causes root dysfunction, with negative
consequences for water and nutrient uptake (Morard and Silvestre
1996
; Gislerød
et al.
1997
). According to Schapira et al. (
1990
), the oxygen dissolved in the nutri-
ent solution of the cucumber crop was depleted within approximately 60 min (25 g
fresh roots per liter nutrient solution at 20 °C). This process, which is driven by root
respiration and microbial activity, is affected by factors such as the nutrient solu-
tion temperature, root biomass, light and CO
2
concentration (Schnitzler and Gruda
2002
) as well as the stage of plant growth. Whereas, for instance, young tomato
plants were able to adapt to hypoxia in the root environment and survive, mature
plants wilted 2 days after aeration interruption in a hydroponic system and conse-
quently died rapidly. Hypoxia in the root environment can result in decrease in leaf
photosynthesis, changes in the transpiration rates and efficiency of the photosystem
II and a slow change in leaf diffuse reflectance (Kläring and Zude
2009
).
Morard and Silvestre (
1996
) reported that root asphyxiation is difficult to carry
out in a substrate culture as plants exhibit considerable tolerance to temporary hy-
poxia and anoxia (several hours) and greenhouse growers have expressed concern
that the oxygen content of nutrient solutions may be sub-optimal for plant growth
(Ehret et al.
2010
). Ehret et al. (
2010
) investigated the oxygen enrichment of the
irrigation solution of cucumbers and pepper, grown in sawdust, and found that in
only one instance out of three trials enrichment increased the yield of cucumbers
and that there was no effect of enrichment on the pepper yield. Gruda et al. (
2008
)
reported that individual factors such as organic substrate, irrigation, and aeration
caused changes in CO
2
concentrations in the root zone of tomatoes and cucumbers.
