Impact of setback distances on transport and antibiotic resistance profiles of fecal indicators from manure-amended fields

Authors: Durso, Lisa; Gilley, John; Meyers, Morgan; Miller, Daniel; LI, XU - University Of Nebraska; SCHMIDT, AMY - University Of Nebraska

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2020
Publication Date: 9/22/2020
Citation: Durso, L.M., Gilley, J.E., Meyers, M.A., Miller, D.N., Li, X., Schmidt, A.M. 2020. Impact of setback distances on transport and antibiotic resistance profiles of fecal indicators from manure-amended fields. Agrosystems, Geosciences & Environment. 3:e220081. https://doi.org/10.1002/agg2.20081.
DOI: https://doi.org/10.1002/agg2.20081

Interpretive Summary: As livestock production operations become larger and more concentrated cost-effective manure application becomes an increasing challenge, and there is pressure to maximize the amount of land to which manure is applied. One management strategy that has been widely used to address environmental and water quality issues is the use of setback distances. Setbacks are guidelines instructing a minimum distance be maintained between manure application and surface waters. They are commonly used to manage nutrient contamination of surface waters, however the utility of setbacks for reducing microbial inputs remains unclear. Here we evaluated the efficacy of five setback distances in no-till wheat residue plots for reducing runoff fecal indicator concentrations from swine manure-amended fields. Also, because there is increasing interest in the use of water quality indicators to evaluate antibiotic resistance in environmental systems, E. coli and Enterococcus isolates were collected, and evaluated for resistance to twelve antibiotics. Although there were significant differences in the runoff from pre- and post- manure application time points, no significant differences were observed for any of the five setback distances measured (range 4.9-23.2m), even though differences had been observed for nutrients at these same distances. Antibiotic resistant E. coli and Enterococcus were isolated from the manure, pre- and post-application runoff, indicating presence of antibiotic resistant fecal indicators in both manure and in non-manured soils. Source attribution remains difficult, although manure had a higher percentage of isolates displaying resistance.

Technical Abstract: Although the land application of livestock manure has numerous agronomic benefits, runoff from manured fields can degrade water quality. Setbacks are guidelines instructing a minimum distance be maintained between manure application and surface waters. They are commonly used to manage nutrient contamination of surface waters, however the utility of setbacks for reducing microbial inputs remains unclear. Here we evaluated the efficacy of five setback distances in no-till wheat residue plots for reducing runoff fecal indicator concentrations from swine manure-amended fields. Also, because there is increasing interest in the use of water quality indicators to evaluate antibiotic resistance in environmental systems, E. coli and Enterococcus isolates were collected, and evaluated for resistance to twelve antibiotics. Although there were significant differences in the runoff from pre- and post- manure application time points, no significant differences were observed for any of the five setback distances measured (range 4.9-23.2m), even though differences had been observed for nutrients at these same distances. Antibiotic resistant E. coli and Enterococcus were isolated from the manure, pre- and post-application runoff, indicating presence of antibiotic resistant fecal indicators in both manure and in non-manured soils. Source attribution remains difficult, although manure had a higher percentage of isolates displaying resistance.