Coupling effects of irrigation and nitrogen levels on yield, water and nitrogen use efficiency of surge-root irrigated jujube in a semiarid region

Jujube (Zizipltus jujube MilL) is one of the most optimal fruit trees for economy and ecology in many semiarid regions. However, with water as a scarce resource, the strategy for irrigation and applied nitrogen (N-app) management need to be identified. The goal of this project was to determine the effects of irrigation and N-app on jujube yield, water use efficiency (WUE) and agronomic nitrogen use efficiency (ANUE), and the optimal level of soil water content (SWC) and N-app for jujube under surge-root irrigation (SRI) in a semiarid region. Experiments were conducted during the jujube growing seasons (May-October) of 2014 and 2015 in northern Shaanxi in China that included three levels of SWC, i.e. 60-85%theta (I-1) (mass water content, simplified as %0), 50-75%theta (I-2), 40-65%0 (I-3), and four levels of N(app )i.e. 0.75 (N-1), 0.50 (N-2), 0.25 (N-3) and 0.00 kg N plant(-1 )(N-4). The treatments were arranged in a strip-plot design with complete randomized blocks with three replications. For both years, irrigation and N-app, had significant (P < 0.05) effects on yield, WUE and ANUE, while the interaction effect of irrigation and N-app on WUE and ANUE was significant (P < 0.05), and significant on yield in 2014 but not in 2015. In both years, maximum yield (10.16 and 9.81 kg plant(-1), respectively) occurred in 60-85%0 and 0.50 kg N plant(-1) , maximum WUE were 3.75, 4.43kg(3) when SWC level and N-app were 40-65%0 and 0.50 kg N plant(-1), while maximum ANUE were 2.21, 2.88 kg kg(-1) when SWC level and N-app rate were 50-75%0 and 0.25 kg N plant(-1), respectively. The dualistic and quadric regression equations of irrigation amount and rate of N-app indicate that the yield, WUE and ANUE of jujube cannot reach the maximum at the same time. Irrigation-N app input optimization model shows that three combinations of likelihood functions can all be used for the comprehensive management of SRI for jujube. Considering the coupling effects of irrigation and N-app on yield, WUE and ANUE in 2014 and 2015, the SWC level shall be controlled in 50-75%8 and the N-app rate is 0.42 kg N plant(-1), which can be as the suitable strategy of irrigation and N-app management for the maximum comprehensive benefits of yield, WUE and ANUE for jujube under SRI in a semiarid region.