University of California

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Remediation and Recovery Measures to Expedite Plant or Replant of Tender Greens Following Soil Contamination by Salmonella enterica

Adrian Sbodio (Department of Plant Sciences; University of California, Davis)Jeremy Roland (Department of Plant Sciences; University of California, Davis)Janneth Pinzon (Department of Plant Sciences; University of California, Davis)Chelsea Kaminski (Department of Plant Sciences; University of California, Davis)Renee Leong (Department of Plant Sciences; University of California, Davis)Trevor Suslow (Department of Plant Sciences; University of California, Davis)

Contamination by soil amendments, flooding, contaminated irrigation water, or other sources has resulted in substantial losses of abandoned tender leafy greens for packaged salads.

We hypothesize that short-duration, low-residue cover crops, solarization, or a combination will be effective in the practical elimination of Salmonella enterica contamination in soil.

Replicated 2 x 5 m plots were inoculated with chicken manure/litter containing an attenuated Salmonella at 10^3 or 4 CFU/g. Plots were treated using solarization or by cover crops. For solarization, plots were covered with clear polymer for 36 days. Cover crops (Buckwheat, Mustard and Canola) were grown up to 50 days. Following incorporation, soil was sampled before plots were replanted with baby spinach.

Trials in clay loam soil revealed limited difference between the fallow controls and cover cropped plots. Unlike our preliminary trials in a high organic matter soil, the die-off of inoculated S. enterica occurred within 30 days. This represented greater than 3-log reduction from applied inoculum levels, intentionally low to reflect a ‘real-world’ natural contamination incident. For solarization, Salmonella enterica was not detected in any covered plot at 39 days whereas 100% of the non-solarized plots were positive for the applied Salmonella. Temperatures at 6 cm under the polymer row covers reached 42-45C during daily cycles while non-covered plots did not exceed 33C. In plots where baby spinach was re-planted, no contamination was detected at harvest.

To determine the practical strategy that will enhance remediation of Salmonella contaminated soil and prevent subsequent product contamination following replant of leafy greens.

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