Unravelling the mechanism of pathogen inactivation during anaerobic soil disinfestation

Anaerobic soil disinfestation (ASD) for the control of multiple soilborne pathogens is a viable alternative to the application of biocides and soil steaming. ASD implies soil wetting, incorporation of fresh organic matter, and covering with airtight plastic foil for several weeks. To speed up the whole process, Thatchtec has developed a procedure based on defined agricultural products (referred to as Herbie). To further optimize ASD, the mechanism of pathogen inactivation should be unraveled. Therefore, we performed an incubation experiment in 11-L polypropene containers with 6 soil types (glacial sand, dune sand, river clay, marine loam, peat soil, and an artificially composed soil lacking any organic matter) in triplicate. After wetting the soil to field capacity, Herbie was added to it (equivalent to 4 g crude protein L-1 soil) and containers were filled with soil (8 L, head space 3 L). A similar treatment without Herbie served as control. Nylon mesh bags containing cysts of potato cyst nematode (PCN; Globodera pallida) were added and the containers were sealed off. Destructive sampling was performed 3, 7, 14, and 28 d after start of the experiment and biotic (cyst content survival, free-living non-plant parasitic nematode community, total and functional groups of bacteria, fungi and protozoa) and abiotic (organic matter, pH, nutrients, EC, fatty acids) parameters measured. Additionally, concentrations of several gases (O2, H2S, CH4, CO2, NH3, N2O) were measured in the head space before each destructive sampling. Survival of eggs within the cysts declined in all treatments to level