Effects of nitrogen management on yield, sugar content and nitrogen use efficiency in rainfed and irrigated sugar beet in China: A meta-analysis

Sugar beet ( Beta vulgaris L.) is a globally significant sugar crop. Although water and nitrogen (N) jointly regulate sugar beet growth, a quantitative understanding of their interactive effects on rainfed and irrigated systems at a regional scale remains limited. In this study, we synthesized 287 datasets from 42 field experiments in China through a meta-analysis to quantify the effects of N management on taproot yield (TY), sugar yield (SY), sugar content (SC), and nitrogen use efficiency (NUE). The results showed that N application significantly increased TY by 29.3% and SY by 23.3%, while SC reduced slightly by 4.5% ( p >0.05). Irrigated systems exhibited greater yield benefits, with increases of 30.8% in TY, and 26.8% in SY, accompanied by minimal SC loss (-1.5%), outperforming rainfed systems, in which SC decreased by 11.2%. For rainfed systems, the optimal practice involved N application rate of 50-100 kg N ha -1 combined with high-frequency topdressing (≥3 times). In contrast, for irrigated systems, omitting basal N and splitting 200-250 kg N ha -1 into two topdressing events was optimal for achieving both high yield and high NUE. Subgroup analyses and Random Forest modeling further identified distinct key regulatory factors. In rainfed systems, annual precipitation and planting density were the primary regulators of TY, whereas K 2 O application rate and mean annual temperature were crucial for SC. In irrigated systems, irrigation amount and soil organic matter determined variations in TY, while N application rate and frequency were the major factors influencing SC. Overall, this study provides region-specific strategies to achieve high yield, quality, and NUE in sugar beet production.