Location: Water Quality and Ecology Research
Title: Fecal bacterial losses in runoff from conventional and no-till pearl millet fertilized with broiler litter Authors
|Nuti, C -|
Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 25, 2013
Publication Date: N/A
Interpretive Summary: Herbicide applications to recently planted fields often require that the herbicide is irrigated into the soil to prevent its loss during storm events. In conjunction with the herbicide application, manure is often broadcast as fertilizer. This agricultural practice of irrigating herbicides into the soil increases the surface soil water content that in turn can lead to increased storm water runoff and increased numbers of fecal bacteria into surface waters. USDA-ARS scientists at Tifton and Watkinsville, GA designed a rainfall simulation experiment to determine if differences in quantities of manure bacteria in storm water runoff from conventional tillage and no-till management practices would be observed after herbicides were incorporated into soil by irrigation. Although results of this experiment indicated that total runoff from the conventional tillage system was 3-times greater than runoff from the no-till system, the quantities of E. coli and Salmonella in runoff from the two tillage practices were not different. Percent recovery of Salmonella was, however, more than ten thousand times greater than recovery of E. coli. This disparity in recovery between these two fecal bacteria provides evidence that E. coli, as a standard indicator of pathogen contamination, may not be effective at indicating risk to public health. This is important information for state and federal environmental protection agencies and managers of watersheds impacted by agriculture.
Technical Abstract: Georgia farmers are increasing preemergence applications of soil residual herbicides to control glyphosate resistant weeds. To be effective these herbicides must be activated by post-application irrigation. Broiler litter is often applied to fields before these herbicides. This wetting-in practice increases surface soil water content and may increase runoff and transport of broiler litter borne fecal bacteria into surface waters during subsequent storm events. Our objective was to determine differences in loads of fecal bacteria, Escherichia coli and Salmonella spp., in runoff from conventional tillage (CT) and no-till (NT) systems after herbicides were watered into an Ultisol fertilized with broiler litter. To replicated 6 m2-plots (n = 3) variable rainfall intensity was simulated for 70 min with composite runoff samples collected every 5 min and analyzed for E. coli and Salmonella spp. Although total runoff from the CT plots was significantly greater than from NT plots, no differences in total load of E. coli and Salmonella were observed. No differences in percent of total loads of E. coli and Salmonella recovered in runoff between tillage systems were observed. Total percentage of Salmonella recovered in runoff from both tillage systems was, however, four log10 orders of magnitude greater than the percentage of E. coli that was recovered. Difference in percentage recovered between the fecal indicator bacterium, E. coli, and the pathogen, Salmonella, underscores an apparent difference in hydrologic transport characteristics of these two fecal bacteria and casts doubts on the efficacy of E. coli as an indicator of risk to public health.