Purpose: To investigate the effects of irrigation, fertilization and planting practices with/without stakes or polyethylene mulch on Salmonella contamination of tomatoes in the field.
Methods: Experiment A was conducted by split plot design with irrigation sources as main plots and planting practices as sub-plots with 720 plants in total. Subplot planting practices included staked with mulch (SP), staked without mulch (SW) and non-staked without mulch (NW). For experiment B, a randomized complete block design was used with four fertilization/planting practices (conventional/SP, poultry litter ash/SP, poultry litter/SP and poultry litter/NW) in each of the four blocks with 960 plants in total. Irrigation water, plant rhizosphere, branches, and fruits were sampled for Salmonella detection. Bacterial population was measured by the most probable number method (MPN).
Results: In experiment A, no Salmonella were isolated from well irrigation water or the corresponding field plants. Salmonella populations (MPN/l) in pond irrigation water were higher in August and September (0.34 and 0.54) than October and November (0.068 and <0.033). Similarly, Salmonella population/contamination ratio of plant rhizosphere/branches increased from August to September and fell thereafter. In experiment B, no Salmonella were isolated from conventional or ash amended soils or the plants grown on them. The bacterial population in the rhizosphere of plants grown on poultry litter amended soils decreased from 480 to 0.34 MPN/kg during the study. In both experiments, rhizosphere Salmonella population was highest in SP plots, while Salmonella was only isolated from the branches of NW plants. No contaminated fruits were detected.
Significance: These field experiments provide insights into the control of Salmonella contamination on tomatoes and statistical data for risk analysis.