Effect of different manure application methods on movement of faecal bacteria in surface and subsurface water and their fate in an agricultural tile drainage system
The application of livestock manure to agricultural lands is a common method of waste disposal and nutrient recycling. However, it is considered one of the major non-point sources of microbial contamination of potable and recreational waters. A research study was designed to assess different manure application methods for their ability to mitigate surface and subsurface movement of pathogenic bacteria in manure-amended soils and to assess the fate of these pathogenic bacteria in an agricultural tile drainage system. Soil and water samples from a field experiment treated with liquid swine manure were monitored for 'Escherichia coli, Clostridium perfringens' and ' Salmonella' to evaluate the effectiveness of different manure application methods for minimizing the potential contamination of surface and subsurface waters. The possibility of biofilm formation by manure-borne pathogenic bacteria in the tile drainage system subsequent to the land application of manure was assessed by laboratory-based experiments with an environmental strain of ' E. coli' isolated from liquid swine manure. The spring-manure application showed a rapid decline of 'E. coli' and 'Salmonella ' in all soils treated with manure. The prolonged persistence of ' C. perfringens' in soils in both the spring and fall manure applications suggested that it is not an appropriate indicator for recent faecal contamination. The die off rates of 'E. coli' after incorporation of manure were not significantly different from non-incorporation treatments. Manure applied on pre-tilled soil without incorporation appeared to have high initial concentrations of 'E. coli' and ' C. perfringens' concentrations within run off mixing zone (0-2 cm) compared to other application methods evaluated in this experiment. However, pre-tillage (without incorporation) was the most effective method for mitigating transport of manure-borne pathogens to subsurface waters during the initial contamination events. Since incorporation is recommended for reducing ammonia volatilization and for minimizing potential overland flow of faecal pathogens in heavy rainfall events, pre-tillage followed by incorporation is likely the best practice for environmental protection. This study also showed that manure-borne 'E. coli' tended to form biofilms on the surface of agricultural tile drains under temperature and nutrient conditions simulated to represent the environment prevalent in the tile drainage system after manure application.