To address concerns regarding the potential impact of antibiotic use in animal husbandry on antibiotic resistance in humans, we conducted a greenhouse-based study examining uptake of the veterinary antibiotics oxytetracycline (OTC) and monensin (MON) by Tifton 85 Bermudagrass (T85), the most commonly grown forage grass in the southeastern U.S.A. Since oxytetracycline is used in both veterinary and human medicine, its accumulation in animal products could impact human resistance to this antibiotic. Monensin is not used in human medicine but has a high potential for accumulating in the environment. Our research examined antibiotic uptake by forage grass T85, the effect of dairy manure application on its uptake, and antibiotic retention in soil. We compared unspiked, wet dairy manure to wet dairy manure spiked with MON or OTC that was soil surface applied to pots or incorporated into soil. After 6 wk, plant stem/leaf and root tissue, as well as soil samples, were assessed for antibiotic residues using enzyme-linked immunosorbent assay (ELISA). Results confirmed Tifton 85 MON and OTC uptake. Six weeks after adding the antibiotics, the greatest plant matter OTC and MON contents were 157.9 ± 70.6 and 234.4 ± 19.6 µg kg⁻¹, respectively, and 17.6 and 369.5 µg kg⁻¹, respectively, for soil. When spiked with OTC, manure incorporation led to decreased OTC uptake by T85 tissue. Bioaccumulation of these antimicrobials in livestock and in the environment is a potential concern for animal, environmental, and human health.

Land application of manure, while beneficial to soil health and plant growth, can lead to an overabundance of nutrients and introduction of emerging contaminants into agricultural fields. Compared with surface application of manure, subsurface injection has been shown to reduce nutrients and antibiotics in surface runoff. However, less is known about the influence of subsurface injection on the transport and persistence of antibiotic‐resistant microorganisms. We simulated rainfall to field plots at two sites (one in Virginia and one in Pennsylvania) 1 or 7 d after liquid dairy manure surface and subsurface application (56 Mg ha^–1) and monitored the abundance of culturable antibiotic‐resistant fecal coliform bacteria (ARFCB) in surface runoff and soils for 45 d. We performed these tests at both sites in spring 2018 and repeated the test at the Virginia site in fall 2019. Manure subsurface injection, compared with surface application, resulted in less ARFCB in surface runoff, and this reduction was greater at Day 1 after application compared with Day 7. The reductions of ARFCB in surface runoff because of manure subsurface injection were 2.5–593 times at the Virginia site in spring 2018 and fall 2019 and 4–5 times at the Pennsylvania site in spring 2018. The ARFCB were only detectable in the 0‐to‐5‐cm soil depth within 14 d of manure surface application but remained detectable in the injection slits of manure subsurface‐injected plots even at Day 45. This study demonstrated that subsurface injection can significantly reduce surface runoff of ARFCB from manure‐applied fields.