Purpose: This study evaluated the survival of E. coli and naturally occurring Salmonella in field-grown watermelons in unamended soils and soil amended with poultry litter (PL).
Methods: Two trials of 12 individual plots were sampled from May-November 2015. Seedless Exclamation and Liberty watermelons were planted on plastic mulch in soil or in soil amended with one of two types of PL (cake and total clean out) applied at 6725 kg/Ha. In each trial, one half of the plots were inoculated with non-pathogenic E. coli (TVS 355). Soil samples collected weekly (n=1032) and watermelons collected at harvest (n=120 on days 70, 77, and 84) were analyzed for E. coli populations by colony count or MPN, and for Salmonella by enrichment using a modified FDA BAM procedure. Data were analyzed using two-way ANOVA in JMP Pro-11.
Results: Composite soil samples and weather parameters were collected weekly. On day 2, E.coli levels were significantly (P<0.0001) greater in amended soils (7.04 log CFU/g) compared to unamended (4.94 log CFU/g), and remained that way throughout the study. Type of PL did not affect E. coli populations. By day 133, E. coli populations in PL-amended soils were significantly greater (0.51±1.15 log MPN/g) compared to those in unamended plots which were below the detection limit (-0.6 log MPN/g). Salmonella spp. was detected in 36% of soil samples and with increased frequency during July-August (P<0.05). Over the study, more samples taken adjacent to the plastic mulch were positive for Salmonella compared to samples from under mulch (P>0.05). Approximately 50% of watermelons sampled were positive for E.coli with a highest recovery of 2.14 log (MPN/g) from amended-soils. Salmonella spp. was detected on watermelons (16/120) grown in both amended and unamended soils.
Significance: Incorporation of poultry litter provided conditions conducive to survival of E. coli and introduced Salmonella into soil and on watermelons.