Effect of Anaerobic Soil Disinfestation on Salmonella Concentration Using Different Soil Amendments

Salmonella has been shown to survive in soils for extended periods. Anaerobic soil disinfestation (ASD) represents a promising alternative to fumigation used to manage soilborne diseases and pests; however, little is known about ASD's impact on Salmonella. The study aimed to compare Salmonella die-off following inoculation in ASD and non-ASD processed soil and compare Salmonella die-off in amended and non-amended soils following ASD. Two independent experiments were arranged in randomized complete block designs (four replications per treatment). Sandy-loam soil was inoculated with a Salmonella cocktail (5.5±0.2 log CFU/g) and amended with field-applicable rates of rye (R), rapeseed (RS), hairy vetch (HV), or pelletized poultry litter (PPL). Non-amended, anaerobic (ANC) and non-amended, aerobic controls (AC) were performed in parallel. Soils were irrigated to saturation and covered with plastic mulch. ASD was terminated by removal of plastic (3-weeks). Triplicate soil samples were collected pre-ASD and 0, 1, 2, 3, 7, 10, 14, 21, 28, 31, 35, 38 and 42d post-ASD. Post-ASD soil was irrigated weekly. Salmonella was quantified using standard methods and a modified MPN enrichment protocol. Concentrations between treatments and time-points were analyzed for significance (P≤0.05). Separate log-linear models were used to examine effect of amendment and irrigation on Salmonella die-off during ASD and post-ASD. Salmonella concentrations decreased in all treatments during ASD with the greatest decrease being observed in ASD and non-ASD controls. Among ASD-processed, amended soil, the rye and rapeseed amendments had the greatest decrease in Salmonella concentrations. Salmonella concentrations decreased by ~1 log between pre-ASD and post-soil saturation (95% Confidence Interval (CI) =-1.31, -0.99), and by approximately 2 logs between pre-ASD and termination of ASD (CI=-2.14, -1.83). Salmonella concentrations were ~1 log higher in ASD-processed, pelletized poultry litter-amended soil, compared to the ASD control (CI=0.81, 1.26). The average daily die-off rate of Salmonella post-ASD was -0.05 log per g (CI=-0.05, -0.04). Following irrigation, Salmonella concentrations were 0.14 log greater, compared to no irrigation within 7 d (CI=0.05, 0.23). Salmonella serovar distribution differed by treatment, with >70% survival of Newport in pelletized poultry litter. ASD does not eliminate Salmonella concentrations in soil; instead some amendments may enhance Salmonella survival.