**6. Fertigation**

Principally, soilless crop cultivation is highly susceptible to fluctuations in water availability due to the restricted rhizosphere volume and the risk of rapid salinization processes. In contrast, this technology easily permits collection and reuse of the drainage water. Irrigation water quantity varies from 3 to 6 mm day−1, depending on the current daily weather and evapo-transpiration conditions. The electric conductivity (EC) of the drainage water is carefully monitored, as it is a good indicator for the maintenance of an optimum drainage coefficient of about 50%; a drainage EC increment above a certain predetermined threshold above the irrigation water EC indicates the occurrence of salinization and a need to raise the daily irrigation and the drainage rates, and *vice versa*. To avoid transient water shortage during the day, the daily amount is supplied through three to four pulses. Drip lines, with 1.6 l h−1 emitters every 20 cm allocate the irrigation water along the growbags, and the coir medium provides the hydraulic conductivity required for uniform water distribution among plants.

Strawberries are highly sensitive to salinity. Yield depletion occurs already at EC of 1 dS m−1, with a yield decrease rate of 33% per every further unit of EC increase [21, 22]. Chloride ions are the major salinity component causing damage [23], suggesting not to exceed irrigation water EC of 1.2 dS m−1 and 1% Cl of the leaf dry matter. Therefore, when growing strawberries in warm arid climates, the highest water quality, as well as the lowest EC possible are recommended. Following a few failures with various mixtures of local brackish and fresh water, we exclusively use desalinated water at 0.5 dS m−1. However, in recycling hydroponic systems using greater water rates, where the risk of salinization is reduced higher EC levels may be considered [24, 25].

The alkalinity of the desalinated water used for irrigation is relatively high (pH 7–8), above the optimum pH for strawberry. Alkaline growth media restrict the absorption of essential micronutrients (e.g., Fe, Mn, Zn, and Cu), resulting in vegetative and reproductive growth retardance and poor yield and quality [26]. Earlier attempts to resolve this problem included the use of high- <sup>+</sup> *NH*4 fertilizers; however, the combination of those with occasional high temperature was followed by gradual plant deterioration, which was related to a cascade of rapid sugar depletion and anoxia during <sup>+</sup> *NH*4 metabolism in the roots [27]. This was overcome using a micronutrient-fortified composite liquid fertilizer with sulfuric acid to adjust for the desired pH. In the recent years, we apply commercial liquid composite fertilizer comprised of 4:2.5:6+6 (N:P:K) with a N– <sup>−</sup> *NO*<sup>3</sup> :N– <sup>+</sup> *NH*4 ratio of 9:1, fortified with 600, 300, 150, 22, and 16 mg kg−1 of Fe, Mn, Zn, Cu, and Mo, respectively, plus Ca and Mg at 2% and 1%, respectively. Fertilizer concentration varies from 60 to 150 ppm of N, adjusted to plant size and crop stage. The fertilizer is applied through the irrigation system (fertigation) constantly in every irrigation pulse and provides a stable pH at the desired range of 6–7.

In order to save water and fertilizer and reduce environmental consequences of the drainage water, considerable attempts have been made to recycle the irrigation water. Nevertheless, obtaining this goal requires a careful Nano-filtration of the water to avoid the spread of diseases, as well as continuous monitoring and adjustment of water quality and nutrient concentration and composition. The technological challenge and the subsequent costs did not justify the benefits, so far. Therefore, the drainage water are monitored, collected, and utilized to irrigate other crops, nearby, thus increasing greater use efficiency.
