Tailored release profiles of alginate and pectin beads by embedding compost-extracted humic substances

Humic Substances (HS) isolated from composted horticultural residues (HS-COM) or lignite (HS-LIG) were blended with alginate or pectin to synthesise novel beads with tuned release of phloroglucinol, a compound used to control plant pathogens. We observed that the physical-chemical and release characteristics of the beads depended on the chemical structure of HS and of the polysaccharidic matrix employed, as determined by Nuclear Magnetic Resonance Spectroscopy. Indeed, strong interactions between pectin backbone and HS-COM hydrophilic moieties resulted in beads with tightly packed structure and high resistance to internal pressure upon water adsorption. Conversely, due the hydrophobic nature of HS-LIG, more fragile pectin beads with disordered architecture and a higher phloroglucinol release were synthesised. A bead structure loosening was observed by HS addition to alginate, determining a lower bead resistance to mechanical stress and increasing phloroglucinol diffusion, regardless of HS nature. Overall, our study showed that horticultural residues can be valorised into high added value products, and that novel formulations are provided to sustain crop yields while reducing the agricultural inputs.