Using desalinated water from solar stills to irrigate green beans (Phaseolus vulgaris L.) in different water regimes with an application of 15N stable isotope

POT EXPERIMENT in the open field was conducted to evaluate the performance of a green bean crop under different irrigation water regimes and two types of solar still (Active and Passive). Irrigation water was applied at regimes of 170, 142, and 114 mm in season, representing T1 (100% WHC), T2 (80% WHC), and T3 (70% WHC) from water holding capacity (WHC), respectively. During the measurement months, the average monthly output of active solar still productivity is 1790 ml m -2 with an average overall thermal efficiency (η active ) of 5.9%, while in the passive solar still productivity is 1308 ml m - 2 with an average overall thermal efficiency (η passive ) of 17.6%. The results indicated that desalinated water applied at T1 enhanced growth characteristics, yield, and improved water productivity (WP) and water use efficiency (WUE) compared to T2 and T3 deficit water regimes. Similarly, increasing irrigation water availability to plants improved NPK nutrient uptake by various plant parts. The 15 N/ 14 N ratio analysis revealed that under all irrigation water regimes, the absolute values of the N portion derived from fertilizer were higher in pods, followed by shoots, and then roots. In contrast with the nitrogen derived from fertilizer (Ndff), the absolute values of Ndff in pods, shoots, and roots seem significantly higher under T1 than those indicated at either the T2 or T3 regimes. In this respect, the nitrogen use efficiency (NUE) reached nearly 64% and 51% for pods and shoots under the T1 regime, while those for roots were still negligible. These percentages of NUE in pods and shoots tended to decrease gradually with increasing water deficits (T2 and T3).