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 N0 and N2 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.
Understanding the interactions of plant soil environment and rhizosphere microbial changes are necessary to develop
new strategies for the sustainable agriculture. A field experiment with combination of three water levels and three
nitrogen rates was conducted to investigate the effect of water and nitrogen management on the changes of soil
microbial properties in non-rhizosphere and rhizosphere soils of spinach. Non-Rhizosphere and rhizosphere microbial
diversities were affected by water and nitrogen applications. Evenness index in the no-nitrogen treatment was more
than that of 85 and 170 kg ha–1 nitrogen treatments in the non-rhizosphere or rhizosphere soil. Microbial biomass
carbon in non-rhizosphere soil or rhizosphere soil decreased with the increase of nitrogen application, but showed
the highest value in 16.5% of soil water content, followed by 12.5% and 20.5% of soil water content. Soil microbial
biomass phosphorus content of 85 kg ha–1 nitrogen treatment in the non-rhizosphere soil or rhizosphere soil was
significantly different for 0 and 170 kg ha–1 nitrogen treatments. Nitrification rate increased with the increase of soil
water content in 0 and 170 kg ha–1 treatments. Our results demonstrated that water and nitrogen could impact the
soil fertility and microbial activity of spinach.