2019 ASHS Annual Conference

Anaerobic soil disinfestation (ASD) has proven to be a promising and environmentally friendly alternative to chemical soil fumigation for controlling soilborne pathogens in a variety of crops. The change in soil microbial communities is considered one of the contributing factors for effectiveness of ASD. However, there is limited information about soil microbial ecology as affected by ASD in tomato production systems especially under low soilborne disease pressure. A field trial was conducted to assess the ASD effects on soil microbial communities during field tomato production in Citra, FL. A randomized complete block design with four replications was used, and the ASD treatments included two rates of molasses (6.9 m³ ha^-1 in ASD0.5 and 13.9 m³ ha^-1 in ASD1.0) and composted poultry litter (11 Mg ha^-1 in ASD0.5 and 22 Mg ha^-1 in ASD1.0), along with the chemical soil fumigation (CSF) control. Phospholipid fatty acid analysis was used to assess changes in soil microbial community composition during the production season at 0, 36, 76, and 99 days after transplanting (DAT) and at two soil depths of 0-15 cm and 15-30 cm. Total microbial biomass, Gram negative bacteria (G-), and G+:G- ratio were significantly impacted by the soil treatment × soil depth, soil treatment × time interactions, while actinobacteria, G+ bacteria, general fungi, and arbuscular mycorrhizal fungi (AMF) were significantly affected by the 3-way interaction between soil treatment, sampling time, and soil depth. Significantly lower concentrations of total microbial biomass and G- bacteria were found in CSF compared to the ASD treatments at both soil depths with greater differences at the 0-15 cm soil depth. Total microbial biomass and G- bacteria also showed higher concentrations in the soil at 0-15 cm than at 15-30 cm in both ASD treatments, but the depth difference was not observed in CSF. General fungi and G+ bacteria exhibited significantly higher concentrations in both ASD treatments than CSF at 0 DAT in 0-15 cm. The concentration of AMF in ASD0.5 at 36 DAT and ASD1.0 at 99 DAT in 0-15 cm was significantly higher than CSF at 36 and 99 DAT in both depths. The spatial and temporal changes in soil microbial community might also be impacted by soil nutrient availability. Overall, ASD could result in the preservation of greater beneficial microbial functional groups compared to chemical soil fumigation. Further research using high-throughput DNA sequencing may help identify key soil microbial functional groups.