Growth Characteristics, Water and Nitrogen Use Efficiencies of Spinach in Different Water and Nitrogen Levels

Water deficit and environmental pollution owing to excessive nitrogen use have caused considerable attention. In a field experiment, a combination of three water levels (20, 40 and 60 cm) and nitrogen fertilizer rates (0, 85 and 170 kg ha^-1) was applied. The main objectives of this study were to optimize water and nitrogen application and exploit their interactive effects on the growth characteristics, yield and water and nitrogen use efficiency of spinach. The results showed that water and nitrogen significantly influenced average plant height and leaf area. Total aboveground biomass (TB) was affected by nitrogen fertilizer and TB decreased in water deficit. Adding nitrogen fertilizer amount resulted in higher leaf chlorophyll content and chlorophyll content obtained the maximum value in N2 treatment, but chlorophyll content was not affected by water deficit. Spinach yield was higher at N1 compared with N 0 and N 2 at all water levels. Abundant water supply resulted in the highest spinach yield, but yield reduced at lower water level (W3). The correlation analysis between spinach yield and leaf number was relatively weak (R²=0.58). On the contrast, the correlation analysis between spinach yield and leaf weight showed a correlationship (R²=0.91), indicating that leaf weight was the primary reason for yield increase in all treatments. Nitrogen fertilization significantly decreased NUE in all the treatments. WUE of spinach increased with adding nitrogen application in most conditions.