Inappropriate strategies in water use and nitrogen (N) fertilizer application in apple production can decrease apple yield, water productivity (WP), nitrogen use efficiency (NUE), and quality, leading to severe environmental pollution. However, there is a lack of systematic analysis on the effects of water use and N fertilizer inputs on apple yield, quality, WP, and NUE at the global scale. Therefore, we conducted a comprehensive meta-analysis with 1834 observations from 72 published studies across 18 countries to assess the effects of water use and N inputs on apple yield, quality, WP, and NUE. We aim to quantify the potential for water-saving and N-saving for global apple production. Our results showed that the global average apple yield, organic acids (OA), total soluble solids (TSS), vitamin C (VC), firmness (FN), WP, and NUE were 34.7 t ha, 0.51 %, 13.9 %, 4.7 mg 100 g, 7.4 kg cm, 6.8 kg m, and 214.5 kg kg, respectively. Reducing above-optimal water input to optimal water input may increase apple yield by 19.4 %, WP by 36.1 %, OA by 12.5 %, TSS by 8.4 %, VC by 17.5 % and FN by 9.8 %, respectively. Reducing above-optimal N inputs to optimal N inputs may increase apple yield by 8.9 %, NUE by 48.1 %, OA by 10.7 %, TSS by 6.1 %, VC by 13.3 % and FN by 5.2 %, respectively. The overall global mean water-saving and N-saving potentials for apple production were 20.4 % (136 mm less water irrigated) and 37 % (203 kg ha less N fertilizer used), respectively. Our findings provide guidance for water use and N fertilizer management of apple production and can thus help to improve/ maintain yield and quality for greatly saving water and N fertilizer.

中文翻译：

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优化灌溉和氮肥管理以提高苹果产量、质量、水分生产率和氮肥利用效率：全球荟萃分析

苹果生产中水分和氮肥施用策略不当会降低苹果产量、水生产率（WP）、氮肥利用率（NUE）和品质，导致严重的环境污染。然而，全球范围内缺乏对水分利用和氮肥投入对苹果产量、品质、水分利用率和氮肥利用效率影响的系统分析。因此，我们对 18 个国家的 72 项已发表研究的 1834 项观察结果进行了全面的荟萃分析，以评估用水和氮输入对苹果产量、质量、可湿性水分和氮肥利用效率的影响。我们的目标是量化全球苹果生产的节水和节氮潜力。我们的结果显示，全球平均苹果产量、有机酸（OA）、总可溶性固形物（TSS）、维生素C（VC）、硬度（FN）、WP和NUE分别为34.7吨·公顷、0.51%、13.9%、4.7 mg 100 g、7.4 kg·cm、6.8 kg·m 和 214.5 kg·kg 分别。将高于最佳用水量减少至最佳用水量可分别使苹果产量增加 19.4%、WP 增加 36.1%、OA 增加 12.5%、TSS 增加 8.4%、VC 增加 17.5%、FN 增加 9.8%。将高于最佳氮输入量减少到最佳氮输入量可分别使苹果产量提高 8.9%，NUE 提高 48.1%，OA 提高 10.7%，TSS 提高 6.1%，VC 提高 13.3%，FN 提高 5.2%。苹果生产的全球平均节水和节氮潜力分别为 20.4%（减少灌溉水 136 毫米）和 37%（减少施用氮肥 203 公斤公顷）。我们的研究结果为苹果生产的水分利用和氮肥管理提供了指导，从而有助于提高/保持产量和质量，从而大大节省水和氮肥。