The current scenario of water scarcity leads to a seek for new irrigation strategies that maintain agricultural productivity while reducing the pressure on freshwater resources, especially in the Mediterranean region, which has a structural deficit of water sources. In this study, the effects of irrigation with water from different origins were assessed over six consecutive years in soil salinity indicators, tree physiology and yield of mandarin trees in south east Spain. The following treatments were considered: i) freshwater from the “Tagus-Segura” water-transfer canal (TW or Control); ii) reclaimed water from a wastewater-treatment plant (RW); iii) irrigation with TW, except in stage II of fruit development when RW was used (TWc); and iv) irrigation with RW except in stage II when TW was used (RWc). Soil salinity indicators increased in all treatments with respect to Control, except for TWc in winter. However, this increase only led to reductions in net photosynthesis and stomatal conductance in the RW treatment, while gas exchange parameters of trees from TWc and RWc were not negatively affected. Tree vegetative growth was only affected in the long-term, with trees from the RWc treatment having greater canopies. Yield was increased in the TWc and RWc treatments by 23.1 % and 29.5 %, respectively; while it was reduced by 23.5 % in RW when compared to TW. Likewise, differences among treatments in fruit quality traits were also detected. Our results suggest that combining water from different sources could be a viable alternative for irrigating mandarin trees under semiarid conditions with savings of approximately 50 % of fresh water, although the sustainability of soil health should be ensured. In addition, further research is needed to adapt these strategies to other species and cultivar-rootstock combinations.

中文翻译：

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再生水和淡水结合对柑橘树性能的长期影响


当前水资源短缺的情况导致人们寻求新的灌溉策略，以保持农业生产力，同时减轻淡水资源的压力，尤其是在水源结构性短缺的地中海地区。在这项研究中，连续六年评估了不同来源的水灌溉对西班牙东南部柑橘树土壤盐分指标、树木生理学和产量的影响。考虑了以下处理：i） 来自“Tagus-Segura”输水渠（TW 或 Control）的淡水;ii） 来自废水处理厂 （RW） 的再生水;iii） 用 TW 灌溉，除了在果实发育的 II 阶段使用 RW （TWc）;iv） 用 RW 冲洗，除了在第二阶段使用 TW （RWc）。与对照相比，所有处理的土壤盐分指标均有所增加，冬季 TWc 除外。然而，这种增加只导致 RW 处理中净光合作用和气孔导度的降低，而来自 TWc 和 RWc 的树木的气体交换参数没有受到负面影响。树木的营养生长仅在长期内受到影响，RWc 处理的树木具有更大的树冠。TWc 和 RWc 处理的产量分别提高了 23.1 % 和 29.5 %;而与 TW 相比，RW 降低了 23.5%。同样，还检测到不同处理间果实品质性状的差异。我们的结果表明，在半干旱条件下，混合来自不同来源的水可能是灌溉柑树的可行替代方案，可节省约 50% 的淡水，但应确保土壤健康的可持续性。 此外，还需要进一步的研究来使这些策略适应其他物种和栽培品种-砧木组合。