Fulvic acid modification with phenolic precursors towards controllable solubility performance

Abstract

Fulvic acids possess important properties for soil improvement and take part in processes such as complexation, chelation, buffering, transport of vitamins and minerals, as well as pH effects. However, their high solubility in water results in rapid runoff through soil especially when applied on sandy soils, allowing fulvic acids only a short-term amendment activity. To address this problem, commercial fulvic acid, which has high-water solubility, was modified to tune solubility performance through acid-catalyzed condensation with phloroglucinol and glyoxylic acid. Phloroglucinol acts as a source of aromaticity and as a reactive aromatic compound while glyoxylic acid possesses an aldehyde function, which plays the role of formaldehyde in classical phenol-formaldehyde condensation, and a carboxylic acid functional group, which provides necessary acidity for the self-catalyzed condensation process. The formation mechanism of such oligomers was investigated through NMR, GPC and CPMAS. By modifying commercial fulvic acid using sustainable methods, its solubility can be tuned, enabling controlled and prolonged delivery of beneficial properties to soils, thereby enhancing soil improvement while minimizing rapid runoff and optimizing resource utilization.