Assessment of weak organic acid-based universal soil extractants for determining plant-available cations and phosphorus

Rapid and accurate assessment of plant-available nutrients is essential for effective soil fertility management and can be facilitated by a universal extractant capable of simultaneously solubilizing multiple nutrients and enabling rapid chemical determination.Many conventional universal extractants, however, are constrained by the inclusion of nutrient ions or strong chelating agents that can interfere with subsequent measurements.In this study, we evaluated weak organic acids (0.01 M oxalic, citric, lactic, and acetic acids) as potential universal extractants for plantavailable cations and phosphate.None of the acids interfered with chemical determination, and ion concentrations in these extracts were substantially higher than in water (5-35 times higher on average) primarily due to the release of exchangeable cations and the dissolution of phosphate and divalent cation precipitates.Plant ion concentrations exhibited pronounced species-specific variability.In addition, broad correlations among multiple ions were observed in weak organic acid extracts (e.g., between orthophosphate and K + , Ca 2+ , and Mg 2+ ) but not in water extracts, indicating that these acids can function as effective universal extractants for rapid, precise, and onsite nutrient assessment.