Optimization of water and nitrogen management strategies for jujube under sand tube irrigation based on regression...

Sand tube irrigation (STI) is one of the most considerable irrigation techniques for increasing water productivity in arid areas. However, it is unclear whether there is still room for further improvements in jujube yield and water productivity under STI with different irrigation and nitrogen application levels.

To solve this problem, a two-year field experiment was conducted to investigate the effects of different irrigation and nitrogen applications on soil water storage, water consumption, jujube yield, and fruit quality, as well as water and nitrogen use efficiency under STI, and to determine the optimal irrigation and nitrogen application solution by the entropy weight-based TOPSIS method.

The results showed that irrigation very significantly (p < 0.01) affected average soil water storage under STI over the entire growth period. STI increased jujube yield significantly (p < 0.05) by 18.1% in 2021 and 15.5% in 2022 compared with surface drip irrigation at the same irrigation and nitrogen amount, respectively. Both irrigation and nitrogen very significantly (p < 0.01) affected crop evapotranspiration (ETa), jujube yield, and nitrogen partial factor productivity (NPFP) in both years. The jujube yield increased linearly with irrigation amount, while showing a unimodal trend with nitrogen application. A significant linear relationship (p < 0.01) between ETa and jujube yield was observed in both years. Nitrogen application significantly affected water use efficiency in both years. In addition, STI increased fruit vitamin C content and sugar-acid ratio to some extent compared with surface drip irrigation. However, the overall effect of irrigation water and nitrogen on each quality index was not significant under STI. Under the same irrigation and nitrogen conditions, STI increased average net income by 51.3% compared with surface drip irrigation in both years. Through a comprehensive analysis of the binary quadratic regression equation and entropy weight-based TOPSIS method, the optimal irrigation and nitrogen amounts were 3600 m³ ha^-1 and 370 kg ha^-1, respectively.

The research will provide technical support for the optimal agricultural water and nitrogen management of jujube in arid areas.