Crushed, squeezed, or pressed? How extraction methods influence sap analysis

Background. Sap analysis provides a fast and promising approach to diagnosing plant nutritional status. However, methodological gaps remain a crucial obstacle to its widespread adoption. Understanding how different extraction methods influence sap composition is key to improving the consistency and diagnostic reliability of this technique. Methods. Five extraction methods were compared based on a range of chemical and physical parameters of broccoli petiole sap. Multiple statistical approaches were used to evaluate method effects on individual parameters and their inter-relationships. Results. The extraction method had a significant impact on sap chemical parameters, affecting mean values as well as variability and distribution shapes. Conversely, the physical ones, such as sap color and dry matter attributes, showed a lower degree of variation across methods. Relationships among these traits were observed; however, the consistency of patterns varied depending on the method. Integrating all data improved models fit compared to independent analyses, while raising concerns about aggregation bias driven by method-specific effects. Overall, these results suggest that refining method selection could enhance both diagnostic reliability and the depth of interpretive analysis. Conclusion. Despite the critical impact of extraction methods on diagnostic outcomes, their importance has been historically overlooked in the design of sap analysis protocols. Neglecting these methodological aspects may compromise the integrity of research findings and undermine fertilizer management decisions in real-world scenarios. This study calls for rethinking current sap analysis practices, raising awareness of methodological variability and encouraging the development of robust, standardized approaches for reliable and comparable sap-based diagnostics.