Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: 4/13/2016
Publication Date: 4/27/2016
Citation: Stocker, M.D., Pachepsky, Y.A., Hill, R., Shelton, D.R. 2016. Remval of fecal indicator bacteria from manured soils under simulated rainfall events spaced in time. BARC Poster Day. 27th Annual Beltsville Poster Day, National Agriculture Library, April 27, 2016..
Technical Abstract: Available information about the release of bacteria from manure under rainfall is obtained predominantly from experiments with freshly applied manure. In reality, manure may stay on fields for some time before being plowed in. Several rainfalls may occur during this time. Rainfalls subsequent to the first one lead to the release of bacteria both from manure and from the thin mixing layer (0-1cm) on the soil surface where bacteria accumulate after the first rainfall. It is not known whether the numbers of fecal indicator organisms released during subsequent rainfalls are larger or smaller than the numbers released during the first rainfall. Two phenomena affect subsequent release. On one hand, it was found that E. coli can experience substantial growth in field-applied manure during the first week or two. On the other hand, manure left open to elements ages and may become crusted which hampers release. We designed laboratory experiments to observe both phenomena in detail. Soil-filled boxes were treated with either dairy cow slurry or solid manure and then received simulated rainfall. Runoff and infiltration samples were collected at 5-minute intervals for one hour. Soil boxes were then stored at a greenhouse for either one or two weeks before receiving a subsequent rainfall application. Soil cores were taken before and after rainfall at depths of 0-1, 1-2, 2-5, and 5-10 cm and then for one month following the final rainfall event. Preliminary results indicate a near 10-fold reduction in concentrations of bacteria removed in surface runoff in the second rainfalls. E. coli concentrations in infiltration waters appear similar between the 1st and 2nd release events. Differences in release patterns were observed for slurry and solid manures. However, with both manure consistencies, concentrations of E. coli in the soil grew between rainfall events whereas enterococci populations experienced immediate exponential decline. Aging appears to be a factor that leads to the decrease of bacteria removed from manured areas despite growth of E. coli in the soil.