Research has shown that compared to traditional surface application, manure soil subsurface injection significantly reduces nutrient input to the aquatic environment; however, it is less known if it can reduce surface losses of manure-associated antibiotics. Two rainfall simulation field investigations were conducted, first in the fall when soil was dry due to limited rainfall and then in the following spring when the soil was moist due to frequent rainfall. The goal of these investigations was to monitor the field surface runoff and soil dissipation of four antibiotics commonly used in animal production. Dairy manure with antibiotics (pirlimycin, tylosin, chlortetracycline, and sulfamerazine) was applied at an agronomic N rate via surface application and subsurface injection. On each plot, a simulated rainfall (70 mmh<sup>-1</sup>) was conducted on days 0, 3, and 7 after manure application and 30-min runoff was collected. Soil samples (0-5 and 5-20 cm) were collected before, on the day of, and 5, 14, 60, and 150 days after the simulated rainfall. Target antibiotics in runoff water, runoff sediment, and soil were qualified and quantified using ultra performance liquid chromatography-tandem mass spectrometry (UPLC/MS/MS). Compared to manure surface application, manure subsurface injection reduced surface runoff loss of antibiotics by at least 47, 50, 57, and 88% for sulfamerazine, chlortetracycline, pirlimycin, and tylosin, respectively (<i>p</i>&lt;0.05). This reduction was more significant in the spring. The pirlimycin loss from subsurface-injected plots was 1.1±0.32% and 0.02±0.01% in the fall and spring, respectively, while that from surface-applied plots was 2.6±0.31% and 8.9±3.9%, respectively. Compared to manure application right before a rain event, application 3 or 7 days before a subsequent rainfall reduced surface runoff of antibiotics by 9 to 45 and 11 to 43 times when manure was surface applied and subsurface injected, respectively. More than 50% of all initially added antibiotics in soil via manure application dissipated within 14 days after application. To decrease input of manure-associated antibiotics to the aquatic environment, the following manure land management strategies are recommended: avoidance of manure application within 3 days before rainfall and subsurface injection especially during the spring season when there is frequent rainfall.

Environmental fate of antibiotics - impact of manure land application methods

255th National Meeting (2018)

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