Submitted to: American Society of Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 8/4/2010
Publication Date: 10/31/2010
Citation: Unger, I.M., Goyne, K., Kremer, R.J. 2010. The Effects of Veterinary Antibiotics On Soil Microbial Community Function in Vegetative Buffers and Cropland [abstract]. American Society of Agronomy. 2010 CDROM. Interpretive Summary:
Technical Abstract: Antibiotics administered to livestock for therapeutic or prophylactic uses often pass intact through the G.I. tract of the animal. These antibiotics are often introduced to agricultural ecosystems via land application of animal waste from confined animal feeding operations. Subsequently, the antibiotics enter soil, surface water and groundwater and may pose a risk to environmental processes. Agroforestry and grass buffer systems may mitigate the distribution or may enhance the degradation of veterinary antibiotics. In particular, root exudates, by providing an additional carbon source, may reduce effects of introduced antibiotics by enhancing microbial growth and potential degradation of the antibiotics. However, shifts in microbial community characteristics may occur as those species sensitive to antibiotics are suppressed. Because little information is available on effects of antibiotics applied to soil, we examined the impacts of different concentrations of oxytetracycline and lincomycin on microbial activity in soil managed under agroforestry, grass buffer, and cropping systems. Soils were collected from 0-10 cm depth from agroforestry sites, grass buffers, and cropped fields located at the University of Missouri Greenly Memorial Research Center, Novelty MO (40°01’N, 92°11’W). Bulk soil samples were moist sieved and then divided into individual jars for each treatment combination. Soils from each land management type were amended with oxytetracycline hydrochloride, lincomycin hydrochloride, or no antibiotic; each antibiotic was applied at three concentrations (5 mg kg-1 soil, 50 mg kg-1 soil and 200 mg kg-1 soil) and all treatment combinations were replicated four times. The amended soils were incubated at ambient temperature and samples were collected at 0, 3, 7, 14, 21, 28, 35, 49 and 63 days. Each sample was tested for soil microbial function using Biolog ECO microplates and dehydrogenase and fluorescein diacetate hydrolytic enzyme assays. Although results from the complete incubation study will be reported, a surprising preliminary observation suggests that the microbial community associated with the agroforestry system metabolizes oxytetracycline hydrochloride applied at 200 mg kg-1 soil. This was an unexpected response, however, few tests of this nature have been conducted with oxytetracycline. Further analyses will allow detection of changes in the microbial community that might account for metabolism of oxytetracycline at high concentrations in soil. Overall, our results provide initial guidance for selecting certain management practices that may help minimize potential detrimental effects of antibiotics reaching the environment through application of animal manures.