Microbial Transport In Surface Runoff From Manure-Amended Soils.

Surface application of manure to agricultural soils can contribute pathogens to runoff water. This rainfall simulation study assessed Salmonella and E. coli in surface runoff from packed stainless-steel soil boxes (100 cm long x 20 cm wide x 5 cm deep) amended with dairy slurry, liquid swine manure, poultry litter, and composted poultry litter. Two rainfall-simulation events were conducted four days apart with manure-amended soil (surface applied at a rate of 150 kg N ha^-1) and rainfall was delivered at 7 cm h^-1 for 40 minutes. Runoff water was collected from soil boxes and analyzed for the presence of Salmonella and E. coli. These bacteria were not detected initially in poultry litter or poultry compost, but E. coli was detected in runoff water from poultry compost-amended soil in a range of 0.40-1.15 log₁₀ CFU ml^-1. However, initial concentrations of Salmonella and E. coli in dairy slurry were 4.60 and 6.61 log₁₀ CFU g^-1, respectively, whereas initial concentrations of these bacteria in liquid swine manure were 4.08 and 5.08 log₁₀ CFU ml^-1, respectively. Salmonella and E. coli were both detected in runoff water from dairy slurry- and liquid swine manure-amended soil during the first rainfall simulation event at concentrations of 2.0-3.2 log₁₀ CFU ml^-1 and 4.0-4.3 log₁₀ CFU ml^-1, respectively. Salmonella was not detected in runoff water from the second rainfall simulation, but E. coli was detected at concentrations of approximately 2.6 log₁₀ CFU ml^-1 from the manure-amended soils. Results showed that manure type and initial concentrations of pathogens affected pathogen concentrations in surface runoff water. In addition, pathogen concentrations were greater in runoff water immediately after manure application in comparison to concentrations four days later. This indicates that soil retention or die-off could have contributed to pathogen reduction in the interim.