| Appropriate manure application rates, timing, and methods are necessary to maximize nutrient utilization by plants from manure, while minimizing water resource pollution potential, including that of enteric organisms. A field study focused on the movement of fecal bacterial indicators to receiving tile drains through subsurface bacterial leaching. Specifically, the impacts of different manure management regimes on fecal coliform, fecal streptococcus, and Escherichia coli (E. coli) densities in subsurface tile drain water were examined for three years. Six swine manure treatments were compared with a control treatment where commercial urea ammonium nitrate was applied. Manure treatments included standard fall injection, spring injection, and late winter broadcast at application rates of 168 kg N/ha and 336 kg N/ha. Results indicated that the highest incidence of significantly elevated bacterial levels occurred where manure had been broadcast in late winter at a rate of 336 kg N/ha.; In a secondary soil column study, leachate from intact 20-cm diameter, 30-cm long soil columns receiving fall and spring manure applications at 168 kg N/ha and 336 kg N/ha was analyzed for bacterial densities. Fecal coliform, E. coli, and enterococci densities in leachate from the columns were determined for four weekly irrigation events following manure application. While a positive trend between manure application rate and bacterial densities in leachate was observed, this effect was not generally statistically significant at the 10% level. However, an interaction between the application rate and timing was observed, indicating that an increase in application rate is more likely to cause a greater increase in bacterial contamination in subsurface drainage with spring application than with fall application. Manure applied at 336 kg N/ha during the spring often resulted in significantly higher bacterial levels in leachate than other treatments. Bacterial densities in leachate from fall manure-applied soil columns were significantly lower in comparison with bacterial densities in leachate from the spring manure-applied soil columns during the second, third, and fourth irrigation events. |
