Optimizing Anaerobic Soil Disinfestation through Soil Fermentation Experiments and Modelling

Anaerobic soil disinfestation, a soil pest/pathogen control method where soil is amended with labile organic matter, saturated with water, and covered with plastic film to induce anaerobic conditions to suppress soilborne fungal, oomycete, bacterial, and nematode pathogens, was developed as an alternative to chemical fumigation, which has severe ecological and human health hazards. Known mechanisms of ASD include anaerobic soil conditions, release of toxic volatile fatty acids (VFAs) such as acetic, propionic, butyric, and isovaleric acid under low soil pH; and increased soil solution Fe²⁺ and Mn²⁺ concentrations. However, little is known about the interactive effects of VFAs, dissolved Fe²⁺ and Mn²⁺, and lime applications in suppressing soilborne fungal pathogens. In this study, aqueous incubations of Fusarium oxysporum (Fo) chlamydospores and conidia in solutions containing VFAs and reduced metals followed by similar incubations in water-saturated soils of different textures amended with varying concentrations of different VFAs, Fe²⁺ or Mn²⁺, both with and without CaCO₃ lime was done to examine any interactive fungicidal effects of these substances. This was followed by ASD experiments in which soils of different textures and liming conditions were amended with varying ratios of protein-rich and carbohydrate-rich amendments in centrifuge tubes followed by strawberry pot studies that involved performing ASD treatments using various amendments (dried molasses, wheat bran, spent brewer’s yeast, and Azolla meal) on both Fo suppression and overall strawberry health. Overall, higher VFA and reduced metal concentrations were associated with greater Fo suppression while liming and finer soil texture decreases ASD efficacy. In addition, it was found that healthy and diverse root-associated fungal communities played at least as important a role in safeguarding strawberry health as suppression of Fo by ASD did.