Purpose: This study sought to investigate the effect of a particular farm practice, cover cropping, along with meteorological factors on the survival of generic Escherichia coli and Listeria innocua in organic and transitional organic produce fields.
Methods: Five cover crop and one bare ground (no cover crop) control plots were inoculated with indicator bacteria generic E. coli and L. innocua in fall 2013 and 2014. Soil samples were collected periodically and were enumerated for E. coli and L. innocua by a modified MPN method. Survival analysis and Poisson regression were applied to determine the effects of cover crop, farming system, and meteorological factors on the survival of E. coli and L. innocua in soil.
Results: Survival analysis indicated that cover crop treatment was not a significant factor affecting survival of E. coli in soil. Interestingly, Cox regression revealed that survival of E. coli in soil was significantly associated with precipitation (P<0.001) and farming system (P=0.007). Increasing precipitation increased the survival of E. coli; and, the survival of E. coli in organic plots was longer than in transitional organic plots. For L. innocua, population levels were significantly higher in transitional organic plots as compared to organic plots. Significantly higher population levels were also observed under higher monthly precipitation, relative humidity, and temperature.
Significance: Our analyses revealed that while the effect of cover cropping is minimal, survival of food safety indicator bacteria are influenced by farming system. Moreover, increasing precipitation and humidity may prolong the survival of E. coli and persistence of L. innocua in soil in regions with cold weather.