Purpose: This study examined bacterial transport in runoff from manure-amended soils subjected to rainfall simulation events.
Methods: A rainfall simulation study assessed Salmonella and E. coli in surface runoff from Othello silt-loam soil packed in stainless-steel boxes (0.00002 ha) amended with dairy slurry (DS), liquid swine manure (LSM), poultry litter (PL), and composted PL, (surface-applied, 3 mt/ha), and one treatment of incorporated poultry litter. Four rainfall-simulation events (7 cm/h for 40 minutes each) were conducted at weekly intervals. Salmonella and E. coli were enumerated from collected runoff water.
Results: Initial Salmonella and E. coli populations in DS-amended boxes were 4.60 and 6.61 log CFU/g, respectively, whereas in LSM the populations were 4.08 and 5.08 log CFU/ml, respectively. Salmonella was not detected in PL or PL-compost runoff; E. coli was detected in runoff from PL-compost-amended soil (0.40-1.15 log CFU/ml), and in significantly (P<0.01) greater amounts in runoff from broadcast than incorporated PL-amended soil after rainfall events 2 and 4. Salmonella and E. coli populations detected in runoff water from dairy slurry- and liquid swine manure-amended soil during the first rainfall simulation event ranged from 2.0-3.2 log CFU/ml and 4.0-4.3 log CFU/ml, respectively. E. coli populations in both manure slurries were comparable (2.6 log CFU/ml); Salmonella was not detected in runoff water from the second rainfall simulation event.
Significance: This study shows that manure type influences pathogen concentrations and persistence in surface runoff water collected immediately after manure application and rainfall in comparison to concentrations several days later. This indicates that soil retention or bacterial die-off could have contributed to pathogen reduction in the interim.