Date of this Version
Agrosyst Geosci Environ. 2020;3:e20081.
Although the land application of livestock manure has numerous agronomic benefits, runoff from manured fields can degrade water quality. Setbacks instruct a minimum distance be maintained between manure application and surface waters. They are commonly used to manage nutrient contamination of surface waters; however, their utility for reducing microbial inputs remains unclear. Here we evaluated the efficacy of five setback distances in no-till wheat (Triticum aes- tivum L.) residue plots for reducing runoff fecal indicator concentrations from swine manure-amended fields. Also, since there is increasing interest in the use of water quality indicators to monitor antibiotic resistance in environmental sys- tems, Escherichia coli and Enterococcus isolates were collected, and evaluated for resistance to 12 antibiotics. Seven of the 12 antibiotics evaluated in this study are critically important to human health and another four of the antibiotics evaluated are highly important to human health, according to World Health Organization (WHO) guidelines. Significant differences existed in amounts of indicators from pre- and post-manure application time points; however, no significant dif- ferences were observed for any of the five setback distances measured (range 4.9– 23.2 m). Antibiotic-resistant E. coli and Enterococcus were isolated from pre- and post-application runoff, indicating presence of antibiotic-resistant fecal indicators in both manured and in non-manured soils, although the source manure had a higher percentage of isolates displaying resistance. It remains difficult to provide recommendations for concurrent reduction of nutrient and microbial contaminants.