Optimizing irrigation and nitrogen management enhances yield, resource efficiency, and fruit quality in global citrus systems: A meta-analysis

Inefficient irrigation and excessive nitrogen fertilization undermine citrus productivity, fruit quality, and resource efficiency (Total Water Productivity, TWP; Total Nitrogen Productivity, TNP), while exacerbating environmental risks such as nutrient runoff and eutrophication. Despite extensive research on drip irrigation and integrated water-fertilizer strategies, a global synthesis of water-nitrogen interactions in citrus systems remains elusive due to regional disparities in climate, soil, and farming practices. This study conducts a comprehensive meta-analysis of 1208 experimental observations from 78 peer-reviewed studies across 11 major citrus-countries, which are predominantly characterized by subtropical and Mediterranean-type climates. This study systematically quantifies the effects of optimized water and nitrogen management on citrus yield, fruit quality, TWP, and TNP. At the global scale, citrus production systems exhibit an average yield of 40.4 Mg ha−1, with corresponding TWP and TNP values of 4.0 kg m−3 and 213 kg kg−1, respectively. Key quality parameters exhibited marked regional variation: juice content (20.9—73.5%), total soluble solids (TSS: 6.3—18.7%), maturity index (MI: 1—27), and single fruit weight (17.5—523 g). Optimizing resource inputs significantly enhances crop productivity and quality. Our global dataset analysis revealed that optimizing water input increased yield by 1.7% and TWP by 33.6%. More importantly, reducing nitrogen applications from common excessive levels to an optimal rate boosted yield and TNP by 12%. Both strategies concurrently improved fruit quality. Analysis of the global dataset suggests that mean input levels of 937 mm water and 163 kg ha−1 nitrogen are associated with relatively high productivity and resource use efficiency in the pooled dataset, indicating a balance between maintaining yield and avoiding excessive input use. While these values should not be interpreted as prescriptive recommendations, they provide a useful reference for evaluating current management practices. At these approximate levels, projections indicate potential for 12% water savings (153 mm) and 19% nitrogen reduction (46 kg ha−1) relative to prevailing inputs. Notably, regions such as Pakistan (16% water savings) and the U.S. (10% nitrogen savings) illustrate how resource-saving opportunities vary across contexts. These findings highlight broad patterns that can inform region-specific precision management, rather than universal thresholds. By aligning management practices with crop requirements, this study advances the dual goals of sustainable citrus production—enhancing economic returns through improved yield/quality while mitigating environmental footprints through resource conservation.