Optimization of nitrogen fertilizer application enhanced sugar beet productivity and socio-ecological benefits in China: A meta-analysis

Nitrogen (N) fertilizer is a key driver for improving sugar beet production, however, the comprehensive effect of the N application rate on beet yield and socio-ecological benefits across various sugar beet-producing regions in China is remains unclear. To address this issue, a comprehensive meta-analysis was conducted on 256 data sets from 87 studies published between 1980 and 2024. The goal was to optimize nitrogen fertilizer management for sugar beet production. The analysis revealed a clear correlation between nitrogen application and improved sugar beet yield in China. Nitrogen application led to an average increase in beet yield by 26.93 % and sugar yield by 17.74 %, emphasizing its key role in boosting productivity. The highest increase in beet yield (31.10 %) and sugar yield (21.65 %) were achieved with nitrogen application rates between 100 and 200 kg N ha⁻¹. However, the benefits of increasing nitrogen rates diminished beyond this range, as indicated by reduced agronomic efficiency and partial factor productivity. This suggests a threshold where additional nitrogen offers little yield improvement. Interestingly, the optimal N application thresholds are lower in North China as compared to Northeast and Northwest China. Ecological and social benefits were maximized at nitrogen application rates of 169–188 kg N ha⁻¹, with a clear reduction in diminishing returns. Excessive N application can lead to reduced ecological and social benefits. Site-specific factors, such as soil pH of 6.5–7.5, total N ≤ 1 g kg⁻¹, and available potassium ≤ 150 mg kg⁻¹, further enhanced beet yield by 36.24 %, 33.84 %, and 35.37 %, respectively. Sugar yield was improved by 27.74 %, 26.13 %, 14.98 %, and 21.84 %, respectively, with optimal conditions including total N ≤ 1 g kg⁻¹, soil pH ≤ 6.5, alkali-hydrolyzable N > 120 mg kg⁻¹, and available phosphorus 20–40 mg kg⁻¹. This study provides valuable insights for optimizing N fertilizer usage in sugar beet production, enhancing environmental sustainability, and advancing green agricultural practices, with potential implications for global sugar beet nitrogen management.