Extraction of fulvic acid by citric acid–ethanol method and its biochemical activity

Abstract BACKGROUND With the widespread application of fulvic acid (FA) in agriculture, improving the industrial yield of FA has become an urgent priority. Therefore, it is particularly important to explore efficient and clean process conditions for the factory production of FA from low‐rank coal, as undertaken in this study. Additionally, an in‐depth study of the biological activity of FA was performed to provide a theoretical reference for its practical application. RESULTS Results showed that, when the reaction temperature was 70 °C, the ratio of citric acid to coal was 0.03:1, the ratio of liquid to solid was 10:1 and the concentration of ethanol was 15%, the average yield of FA was about 80‰. Seed soaking with FA promoted seed germination and improved seedling quality. As the concentration of FA for seed soaking increased, the germination potential, amount of reduced tetrazole and root length were reduced, but the relative electrical conductivity and chlorophyll content were increased. CONCLUSION Coal‐based FA was effectively extracted by the citric acid–ethanol method and the yield of FA was relatively high under the optimum conditions. The treatment of cucumber seeds and seedlings with different concentrations of FA effectively promoted seed germination and seedling growth. © 2021 Society of Chemical Industry (SCI).