15N Isotope Labeled Tracking of the Nitrogen Utilization of Apple under Water and Nitrogen Coupling Application in Arid and Semiarid Areas

Abstract

In order to solve the problem of water waste and environmental pollution in arid and semiarid areas, this study aimed to investigate the effects of different water and nitrogen treatments on the growth of apple leaves, photosynthetic physiology, nutrient uptake and nitrogen use efficiency. A two-factor experimental design was used in this experiment. The first factor was three levels of irrigation (40–50%, 50–65%, 65–80% RWC, relative water content) and the second factor was four levels of nitrogen application (0, 150, 300, 600 kg/ha), which were a completely randomized combination. The results showed that irrigation and nitrogen application had significant effects on the growth, photosynthetic rate, chlorophyl and mineral element contents of apple tree leaves, but excessive input of water and nitrogen would restrain the growth of apple tree leaves. The Ndff% of different organs for apple trees were evaluated by 15N isotope tracer technology, and the highest Ndff% value was found in leaves, ranging from 1.01–1.23‰. Next were roots with 0.29–0.43‰, and the lowest Ndff% was found in fruits with 0.03–0.08‰. The calculation results of 15N utilization in apple trees showed that nitrogen use efficiency (NUE) under the medium-water low nitrogen (W1N1) treatment had the highest value with 43.33%. In conclusion, considering the growth physiology and nitrogen utilization of apple trees, it is recommended that a water and fertilizer coupling combination scheme for apple trees in arid and semi-arid areas of the Loess Plateau should be that of a medium-water and medium-nitrogen mode (W1N2, 50–65% RWC, 300 kg/ha).