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

Abstract

Jujube (Ziziphus jujuba 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 (Napp) management need to be identified. The goal of this project was to determine the effects of irrigation and Napp on jujube yield, water use efficiency (WUE) and agronomic nitrogen use efficiency (ANUE), and the optimal level of soil water content (SWC) and Napp 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%θ (I1) (mass water content, simplified as %θ), 50–75%θ (I2), 40–65%θ (I3), and four levels of Napp, i.e. 0.75 (N1), 0.50 (N2), 0.25 (N3) and 0.00 kg N plant−1 (N4). The treatments were arranged in a strip-plot design with complete randomized blocks with three replications. For both years, irrigation and Napp had significant (P < 0.05) effects on yield, WUE and ANUE, while the interaction effect of irrigation and Napp 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%θ and 0.50 kg N plant−1, maximum WUE were 3.75, 4.43kg m−3 when SWC level and Napp were 40–65%θ and 0.50 kg N plant−1, while maximum ANUE were 2.21, 2.88 kg kg−1 when SWC level and Napp rate were 50–75%θ and 0.25 kg N plant−1, respectively. The dualistic and quadric regression equations of irrigation amount and rate of Napp indicate that the yield, WUE and ANUE of jujube cannot reach the maximum at the same time. Irrigation−Napp 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 Napp on yield, WUE and ANUE in 2014 and 2015, the SWC level shall be controlled in 50–75%θ and the Napp rate is 0.42 kg N plant−1, which can be as the suitable strategy of irrigation and Napp management for the maximum comprehensive benefits of yield, WUE and ANUE for jujube under SRI in a semiarid region.