Effects of Swine Manure Application on Bacterial Quality of Leachate from Intact Soil Columns

Excessive application of swine manure on agricultural lands is likely to increase water pollution. Potential impacts of swine manure management on bacterial contamination in subsurface drainage are often difficult to assess in the field. In this study, leachate from intact 20-cm (8-in.) diameter, 30-cm (12-in.) long soil columns receiving simulated fall and spring manure applications at 168 kg N/ha (150 lb N/ac) and 336 kg N/ha (300 lb N/ac) was analyzed for bacterial densities. The fall soil columns were frozen for 7 weeks between manure application and irrigation. Soil columns were collected in sterile galvanized tubing using a Giddings probe and 20-cm bit adapter. 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 the manure application rate and bacterial densities in the leachate water was observed, this effect was not generally statistically significant at the 10% level. However, an interaction between the application rate and timing was observed, suggesting that an increase in application rate is more likely to cause greater bacterial contamination in subsurface drainage for spring application than for fall application. Bacterial densities in leachate were most often significantly higher where manure had been applied in the spring at 336 kg N/ha, versus the other manure treatments. Additionally, less bacterial leaching was observed in fall manure-applied columns as compared to the spring manure-applied columns. 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 at the 10% level during the second, third, and fourth irrigation events.