Abstract
Water deficit and increasing pressure on water resources in semi-arid regions has led to the spread of irrigation with non-conventional water resources, such as desalinated seawater (DSW). The few existent studies to date, mainly carried out in Israel and Spain, have shown that suitable management of irrigation with DSW must be performed to avoid agronomic problems and reductions in crop productivity and fruit quality in the mid-long term. To the best of our knowledge, in the case of citrus, fruit production, and quality, information on the effects of DSW irrigation is not available. In this study, we evaluated the short-term agronomic and economic effects of irrigating a mandarin orchard during two crop cycles (2017–2019) with (i) fresh water (FW), (ii) desalinated seawater (DSW), and (iii) a mix of water composed of 50% FW and 50% DSW. Stem water potential (Ψs < −1 MPa) and gas exchange parameters (net photosynthesis; A > 6.5 µmol/m2/s and stomatal conductance; gs > 65 mmol/m2/s) indicated that trees were well irrigated throughout the experiment. The concentration of Na+ and B3+ in the DSW always exceeded the maximum thresholds for irrigation water proposed in the literature for citrus, and the concentration of Na+ in the leaves exceeded the maximum threshold in summer 2018. Nonetheless, symptoms of toxicity were not observed. Significant differences among treatments were not observed for Ψstem, A, gs, Na+, Cl−, and B3+ in leaves (except in the summer months), yield components, fruit quality, or the economic assessment. The lack of such differences was explained by the large standard deviations caused by the youth of the trees, with figures that on occasion could represent more than 100% of the mean value. These results may justify the agronomic and economic viability of the irrigation of young trees with DSW in the short-term, but further research, considering the effects on adult trees in the long term is still needed.
Highlights
Feeding nine billion people in 2050 will require increasing world food production by 70–100%, which will only be possible under intensive irrigated agriculture [1]
Ca2+, Mg2+, and SO4 2− in the desalinated seawater (DSW) were only 37.3%, 20.4%, and 8.0% of those measured in the fresh water (FW) from Oct-2017 to Sept-2018 and 50.9%, 33.7%, and 21.6% of those measured in the FW from Oct-2018 to June-2019
The boron concentration in the DSW was similar to that found in the FW, a circumstance that was attributed to the low selectivity for B3+ of the one-stage reverse osmosis (RO) process
Summary
Feeding nine billion people in 2050 will require increasing world food production by 70–100%, which will only be possible under intensive irrigated agriculture [1]. A clear example is the Segura River Basin (SRB), an irrigation area of 262,400 ha located in southeastern Spain, which supports an annual structural water deficit above 400 hm ; i.e., 1524 m3 /ha [3]. In this hydrologically stressed region, the compulsory allocation of water creates significant conflicts among aggravated users, with farmers being especially affected during drought periods. In the SRB, 184.3 hm of DSW is annually used for irrigation representing 74% of the total production of DSW in the basin and 11.9% of its agricultural demand [5]
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