Long-term physiological and agronomic responses of mandarin trees to irrigation with saline reclaimed water

•Saline reclaimed water did not affect leaf gas exchange nor plant water status.•Long-term irrigation with saline reclaimed water increased soil salinity.•Long-term irrigation with saline reclaimed water reduced yield.•Saline reclaimed water did not affect fruit quality. In this study, the physiological and agronomic responses of commercial ‘Citrus Clementina cv. Orogrande’ mandarin trees to irrigation with saline reclaimed water (RW) (electrical conductivity≈3.5dSm−1) were evaluated during six consecutive seasons (2008–2013) and compared with those observed in trees irrigated with fresh water from Tagus-Segura” water transfer canal (TW). Irrigation with saline RW significantly increased soil salinity with remarkably substantial increases from the third season onwards, especially in summer measurements. Even though RW had high concentrations of Na, Cl− and B, only leaf B concentrations showed higher values than those of TW treatment, although none of them exceeded the maximum toxic threshold marked in leaves for citrus trees. Stomatal conductance, net photosynthesis and plant water status were not affected by the use of RW. However, irrigation with RW led to a reduction of the vegetative growth, which was greater from the third season. During the first three seasons, RW led to reductions of crop fruit load, which were often associated with an increase in fruit weight, hence maintaining yield and water productivity. However, since 2011, the reductions of crop fruit loads were more prominent and yield and water productivity were significantly reduced. In short, medium to long-term irrigation with saline RW in semiarid conditions negatively affected the soil and trees performance, and hence, suitable management practices should be implemented to ensure the sustainability of soils and mandarin yields subjected to long-term use of these non-conventional water resources.