Effect of Deficit Irrigation with Treated Wastewater on Water Use Efficiency, Nutrient Uptake, and Growth of Pistachio Seedlings in an Arid Area

Yazd province is one of the most important centers for pistachio and seedling production in Iran due to its geographical location and climate. However, this province is also one of the arid and semi-arid regions, facing the serious problem of water shortage. The use of wastewater and deficit irrigation techniques is, therefore, very important for irrigating pistachio seedlings in this arid region. For this purpose, this study was conducted to investigate the effect of deficit irrigation with treated wastewater on water use efficiency, leaf nutrient uptake, and growth of 1-year-old pistachio seedlings. This study was performed as factorial experiment based on a completely randomized design with three repetitions; irrigation water quality was addressed in four levels of treated wastewater (W1), groundwater (W2), 50% treated wastewater and 50% groundwater (W3), and intermittent irrigation with treated wastewater and groundwater (W4). Also, four irrigation levels including deficit irrigation based on 100% (S1), 80% (S2), 60% (S3), and 40% (S4) field capacity were considered. At the end of the experiment, some morphological and physiological traits, such as SPAD in the leaves, relative water content (RWC), electrolyte leakage (EL), stem height and diameter, number of green leaves and leaf area, root fresh and dry weight, water use efficiency (WUE) and the leaf nutrient uptake, were evaluated. Statistical analyses showed that all morphological parameters were higher when irrigation was done with treated wastewater rather than groundwater. The results also suggested that water quality was more effective than deficit irrigation levels on the morphological traits. Also, while SPAD was affected by water quality, RWC and WUE were more under the influence of deficit irrigation levels. Further, physiological growth was higher in those seedlings irrigated on W1S1, whereas the highest WUE was obtained in W1S3. The analysis of variance also showed that the main effects of irrigation water quality and different levels of deficit irrigation, as well as the interaction of these treatments, were statistically significant at the level of 1% on all nutrients uptake in the investigated pistachio seedlings. According to the obtained results, wastewater could compensate for the negative effects of deficit irrigation in the moderate levels of deficit irrigation. The use of wastewater, along with the application of deficit irrigation techniques, can be, therefore, recommended as an important step to solve water shortage problems and increase water use efficiency in arid areas. The results of this study could provide information helpful for establishing orchards by using wastewater under water shortage conditions, especially in arid zones.