Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2009
Publication Date: 10/1/2009
Citation: Guber, A.K., Pachepsky, Y.A., Shelton, D.R., Yu, O. 2009. Fecal Coliform Interaction with Soil Aggregates: Effect of Water Content and Bovine Manure Application. Soil Science. 174(10):543-548. Interpretive Summary: Land-applied manures may contain pathogenic bacteria, which if transported to surface or groundwater can cause public health problems. Transport of bacteria in the environment is strongly affected by their association with soils. Experiments on bacterial attachment to soil are traditionally carried out with sieved soil or with soil primary particles. In reality, bacteria enter soil through relatively large pores and interact with soil particles arranged into larger structural units called aggregates or peds. Although the importance of soil structure for bacterial transport has been widely recognized, limited information exists regarding bacterial interaction with soil aggregates. We found that the interaction of fecal bacteria with soil aggregates strongly depends on whether the aggregates are wet or dry. Many more bacteria became associated with dry aggregates. Also, the presence of dilute manure drastically decreased the number of bacteria associated with aggregates. These results show that the association of bacteria with soil needs to be evaluated using soil aggregates and manure. Furthermore, transport studies conducted with sieved soils in the absence of manure soil may seriously underestimate pathogen transport potential in manure contaminated environments.
Technical Abstract: Aims: To test the hypothesis that fecal coliform (FC) interaction with soil aggregates is affected by aggregate size, water content and bovine manure application. Methods and Results: Tyler loam soil aggregates were separated into fractions of 3.35-4.75 mm, 4.75-7.93 mm and 7.93-9.5 mm. Air-dry and water-saturated aggregates were submerged in water-FC and water-manure-FC suspensions with concentrations of 102, 103, 104, or 105 CFU ml-1 for 24 h. The maximum FC amount was associated with air-dry aggregates in the water-FC suspension; no measurable FC amount was associated with the saturated aggregates in the same suspension. In the water-manure-FC suspension, about 2.5 times more FC was associated with the air-dry soil aggregates than with the water-saturated aggregates. FC amount, associated with air-dry aggregates in the water-manure-FC suspension was about 300 times less compared with amount in the water-FC suspension. FC interaction was not affected by aggregate size. Conclusion: Increased water content of soil aggregates and presence of manure in water-FC suspensions resulted in decreased of FC associated with soil aggregates. Significance and Impact of the Study. Because FC transport in soil generally occurs through interaggregate pores after rainfalls following manure applications, a decrease in bacteria-soil interaction, as a result of soil saturation and presence of suspended or dissolved manure components, can enhance bacterial mobility and increase risk of ground water contamination.