Effect of Saving-water Drip Irrigation and Nitrogen Reduction on Growth and Photosynthetic Characteristics of Young Apple Tree

【Objective】 Reducing water and fertilizer application is critical to developing sustainable agriculture worldwide. This paper investigates the optimal water-saving drip irrigation and nitrogen-reducing fertilization for cultivation of young apple in arid and semi-arid regions in northwestern China. 【Method】 The two-year experiment consisted of three irrigation treatments by keeping soil water content at 75%~90% (W1), 60%~75% (W2) and 45%~60% (W3) of the field capacity. For each treatment, there were four fertilizations by applying N-P2O5-K2O to each plant at 18-12-6 g (F1), 15-12-6 g (F2), 12-12-6 g (F3), and 9-12-6 g (F4). For each treatment, we measured the growth, photosynthetic traits, and water use efficiency of the trees. 【Result】 F2+W2 combination gave the highest plant growth, basal stem growth, and leaf area, demonstrating that a moderate water deficit and fertilization reduction was beneficial to the tree growth. Leaf SPAD started to increase from the budding and flowering stage, with the impact of fertilization on it ranked in the order of F1 > F2 > F3 > F4, and the influence of irrigation ranked in the order of W1 > W2 > W3 at the fruit-set and ripening stages. The F1+W1 combination gave the highest leaf SPAD. Photosynthesis and transpiration increased with the increase in fertilization and irrigation amount. Maximum water use efficiency was achieved in F1+W2 and F2+W2, with its value being 5.16 and 4.81 μmol/mmol, respectively, which were 8.6% and 5.3% more than those in F1+W1. Irrigation amount affected tree growth more than fertilization, and strong correlations were found between growth, leaf area, SPAD, and photosynthetic traits of the trees. 【Conclusion】 The comparative results show that F2+W2 is optimal for young apple tree under drip irrigation. It indicates that a moderate reduction in irrigation and fertilization did not result in a noticeable effect on tree growth and can be used as an improved agronomic practice for apple production in arid and semi-arid regions in Northern China and areas with similar climates.