Effects of different levels of water, salinity and nitrogen fertilizer on growth indices and water use efficiency of spinach

The aim of this study was to evaluate the effects of salinity of irrigation water in interaction with different levels of irrigation water and nitrogen requirements on growth characteristics and water use efficiency of spinach. A combination of five salinity levels (1, 4, 7, 9 and 11 dS/m) with three levels of water requirement including (75, 100 and 125% of irrigation water requirement) and four levels of nitrogen from the source of urea with a purity of 46% (0, 100, 150 and 200 mg/kg soil) under controlled greenhouse conditions in three repetitions were considered as the studied factors. The results showed that salinity in combination with water stress and nitrogen deficiency caused a significant reduction in plant growth. Yield in treatments 75 and 125% of water requirement was 22.7 and 10.8% less than 100% of water requirement, respectively. Salinity in the treatment of 75 and 100% water requirement had a significant effect on leaf area index; such that the treatment of 75% of water requirement with the salinity level 11 ds/m decreased the leaf area index 46% tward control treatment. By increasing the application of fertilizer at the optimal level of 150 mg N/kg soil, plant growth and yield for all salinity levels showed a significant increase. Water use efficiency increased in W1, W2 and W3 treatments at salinity levels 4, 7 and 4-7 ds/m, then decreased significantly with increasing salinity for all treatments of water requirement and nitrogen levels. Also, 125% treatment caused a further reduction in water use efficiency compared to 75% and 100% water requirement treatments for all salinity levels. Finally, the best treatment in terms of water use efficiency was observed in the treatment of 75% of water requirement at moderate salinity levels (4- 7 dS/m).