2018 ASHS Annual Conference

Anaerobic soil disinfestation (ASD) is a non-fumigant pre-plant soil disinfestation technique proposed for the management of soilborne pests and diseases. In Florida, ASD is applied by amending the soil with sugarcane-molasses (C-source) and composted poultry-litter (CPL), irrigation to soil saturation, followed by mulching with totally impermeable film (TIF). While ASD may provide higher yields compared to the standard chemical soil fumigation (CSF), its large-scale application is currently limited by the cost of the C-source. Moreover, there are concerns regarding the fate of the nutrients applied with the amendments combined with soil saturation, especially in terms of nitrous oxide emissions and nutrient leaching. Therefore, a study was performed in Immokalee, FL on fresh-market tomato during the 2015 fall-season to investigate nutrient dynamics. Standard CSF with Pic-Clor 60 was compared with ASD application using two rates of organic amendments: ASD1 (13.86 m³ ha^-1 molasses and 22 Mg ha^-1 CPL) and ASD0.5 (6.93 m³ ha^-1 molasses and 11 Mg ha^-1 CPL), in combination or not with the pre-emergence herbicide halosulfuron-methyl. Treatments were arranged in a split-plot design with four replications. The objective of the study was to determine the impact of the treatments on soil redox-potential, plant growth, fruit production, and nutrient fate. During the three-week treatment, both ASD treatments achieved similar anaerobic conditions, regardless of herbicide application. Nitrous oxide emissions were minimized by the TIF during the three-week treatment, and only immediately after punching were higher with CSF than with ASD. At the same time, both ASD1 and ASD0.5 increased the availability of K in the soil solution compared to CSF. Conversely, 7 days after treatment (DAT), NO₃^- concentrations in the soil solution were 86% lower in ASD compared to CSF. At transplanting (21 DAT), ASD increased P and K soil content compared to CSF, and increases were proportional to amendment rate, regardless of herbicide application. At 58 days after planting, above-ground total plant dry-weight was 82% and 41% higher with ASD1 and ASD0.5 than CSF, respectively; while herbicide application had no effect. Consequently, plant nutrient accumulation was positively affected by ASD and by increasing amendments rate, but it was not influenced by herbicide application. In conclusion, ASD showed lower risk of N loss compared to CSF, while it increased the availability of P and K for the crop. Therefore, the crop fertilization program should be adjusted considering the input of nutrients associated with the application of molasses and CPL.