Global synthesis and multi-site field experiments reveal context-dependent benefits of boron fertilization for sugar beet yield and sugar content

Context Boron deficiency frequently constrains sugar beet growth, root yield, and sugar accumulation, yet the overall magnitude of crop responses to boron fertilization, the conditions under which these responses are maximized, and their agronomic relevance under field conditions remain insufficiently resolved at the global scale. Methods We conducted a global meta-analysis using 2283 paired observations from 76 field studies published between 1959 and 2025 to quantify the effects of boron fertilization on sugar beet root yield, sugar content, and sugar yield, and to identify the major climatic and soil factors associated with response variation. In addition, we carried out multi-site field experiments across 32 sites in Heilongjiang Province, China, to evaluate the agronomic relevance of the global synthesis under practical production conditions. Results Across all studies, boron fertilization increased sugar beet root yield by 10.25% and sugar content by 4.15% relative to the non-boron control. The derived indicator of sugar yield increased by 14.28%, reflecting the combined improvement in root yield and sugar content. Response magnitude varied markedly with environmental and edaphic conditions, with generally larger benefits observed under lower soil boron availability and in relatively cool and moist environments. Subgroup analysis and meta-regression further showed that response patterns differed between fertilization methods, with 1.65–3.00 kg boron ha −1 identified as an agronomically effective range for soil application and 0.25–0.50 kg boron ha −1 for foliar application. The multi-site field experiments in China confirmed an overall positive response of sugar beet productivity to boron fertilization, although the magnitude of response differed substantially among sites. Conclusion Boron fertilization can improve sugar beet productivity by increasing both root yield and sugar accumulation, but its benefits are strongly context-dependent. The main contribution of this study is to define global response patterns and practical application ranges across contrasting environments, thereby providing a quantitative basis for site-specific boron management in sugar beet production.