| Summary: | Two field experiments were conducted to investigate the effects of three drip irrigation regimes (G<sub>1</sub>: 120% crop evapotranspiration (ETc), G<sub>2</sub>: 100% ETc, and G<sub>3</sub>: 80% ETc) and four nitrogen (N) source treatments (S<sub>0</sub>: non-fertilized; S<sub>1</sub>: urea, S<sub>2</sub>: ammonium nitrate, and S<sub>3</sub>: ammonium sulfate on water consumption use, water utilization efficiency, chlorophyll, yield and tubers quality of potato (<i>Solanum tuberosum</i> L.; cv Diamond) under a drip irrigation system during two successive winter seasons (2015/16 and 2016/17)). Nitrogen fertilization was applied at 380 kg ha<sup>−1</sup> as standard application for potato in the investigated area. The highest tubers yield was obtained from potato grown with G<sub>1</sub> S<sub>2</sub> (65.8 Mg ha<sup>−1</sup>), G<sub>1</sub> S<sub>3</sub> (63.6 Mg ha<sup>−1</sup>), G<sub>2</sub> S<sub>2</sub> (64.1 Mg ha<sup>−1</sup>), and G<sub>2</sub> S<sub>3</sub> (62.4 Mg ha<sup>−1</sup>), while the lowest tubers yield was obtained from potato grown with G<sub>3</sub> S<sub>0</sub> (10.1 Mg ha<sup>−1</sup>) and G<sub>2</sub>S<sub>0</sub> (17.4 Mg ha<sup>−1</sup>). Different treatments of N source resulted in a significant increase for water use efficiency (WU<sub>t</sub>E) compared with unfertilized treatment. For the interaction effect, the highest WU<sub>t</sub>E was obtained from potato grown with G<sub>3</sub> S<sub>2</sub> (18.1 kg m<sup>−3</sup>), followed by G<sub>3</sub> S<sub>3</sub> (17.6 kg m<sup>−3</sup>), while the lowest WU<sub>t</sub>E was obtained from plants grown with G<sub>3</sub>S<sub>0</sub> (3.0 kg m<sup>−3</sup>). However, the highest chlorophyll content was obtained from plants grown with G1 and any N source, followed by G<sub>2</sub>S<sub>1-3</sub>, while the lowest chlorophyll content was obtained from those grown with G<sub>3</sub>S<sub>0</sub>. The highest N, S, protein, and P contents in tubers were obtained from plants grown with G<sub>3</sub>S<sub>3,</sub> G<sub>3</sub>S<sub>2</sub>, and G<sub>2</sub>S<sub>2</sub>, while the highest K content in tubers was obtained from plants grown with G<sub>1</sub>S<sub>1</sub> and G<sub>1</sub>S<sub>2</sub>. In concussion, the integrative effects of G<sub>1</sub> or G<sub>2</sub> with S<sub>2</sub> or S<sub>3</sub> is recommended for high productivity, while the integrative effects of G<sub>3</sub>S<sub>3</sub> and G<sub>3</sub>S<sub>2</sub> are recommended for high quality tubers.
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