Preparation of Microcapsules of Wood Distillate Coated with Chitosan and Micronized Biochar: A New Material with Potential for Sustainable Crop Protection and Precision Agriculture

Wood distillate (WD), also known as pyroligneous acid, is a liquid byproduct of charcoal production. It has antimicrobial and antifungal properties thanks to its combination of over 200 components, including organic acids, polyphenols, tannins and others. In this work, microcapsules containing WD coated with chitosan or chitosan and micronized biochar were developed, and their efficacy was tested against the soil-borne fungal pathogen Macrophomina phaseolina. The three products used fit into a circular economy model, and these bio-based microcapsules can be used to promote sustainable agricultural practices. The microencapsulation of WD was carried out via an ion-exchange gelation method, using sodium alginate as the polymer. WD microencapsulation and coating formation were successfully performed, resulting in microcapsules with a size between 600 and 700 µm when dried. Three types of WD microcapsules were produced: uncoated, chitosan-coated and chitosan–biochar-coated. Solubility tests were conducted by measuring the pH of each type of microcapsule in distilled water. It was observed that their solubilization trends were different depending on the type of microcapsules. In vitro growth of M. phaseolina on PDA plates was completely inhibited using WD concentrations of 3–5%. Furthermore, when WD microcapsules were added to a liquid culture medium, those coated with chitosan and biochar induced a significant reduction in M. phaseolina growth.