Optimization of water and nitrogen management for surge-root irrigated apple trees in the Loess Plateau of China

The Loess Plateau is one of the main regions for growing apple trees in China, but a shortage of water resources and low utilization of nitrogen have restricted its agricultural development. A 2-year field experiment was conducted which included three levels of soil water content (SWC), 90-75%, 75-60%, and 60-45% of field capacity, and five levels of nitrogen application (N-app), 0.7, 0.6, 0.5, 0.4 and 0.3 kg/plant. The treatments were arranged in a strip-plot design with complete randomized blocks with three replications. For both years, the water and N-app had significant (P<0.05) effects on leaf area index (LAI), yield, water use efficiency (WUE) and nitrogen partial factor productivity (NPFP) while the interaction effect of water and N-app WUE first increased, then decreased as N-app increased, while NPFP tended to decrease, but the trend of LAI with different N-app first increased, then decreased, but the yield showed different trends as the SWC increased. The dualistic and quadric regression equations of water and N-app indicate that the yield, WUE and NPFP cannot reach the maximum at the same time. Considering the coupling effects of water and N-app on yield, WUE and NPFP in 2017 and 2018, the SWC level shall be controlled in 75-60% of field capacity and the N-app is 0.45 kg/plant, which can be as the suitable strategy of water and N-app and other regions with similar environments.