Alterations in total microbial activity and nitrification rates in soil due to amoxicillin-spiked pig manure

Most veterinary drugs enter the environment via manure application. However, ecotoxic effects of antibiotics are varying as a function of their physicochemical characteristics and for most antibiotics it is still unclear how these substances interact with soil biota. It was the aim of the present study to investigate effects of manure containing different concentrations of the antibiotic amoxicillin (AMX) on microbial-community function in two different soils over an incubation time of 18 d. Therefore, soil respiration, potential nitrification, and the products of N turnover were measured. We could show that CaCl₂-extractable amounts of AMX in soil are low, even shortly after the application of high doses together with manure. Thus, not surprisingly basal respiration in soil was not influenced by the addition of the antibiotic with manure. In contrast, mainly shortly after manure addition the kinetic of substrate-induced respiration was clearly shifted by the treatments depending on the presence of AMX in the manure. Potential nitrification rates in the two different soils were not significantly affected when data were related to the overall incubation time by the application of AMX to the manure. However, shortly after the addition of the manure containing AMX, a tendency to lower turnover rates was visible compared to the application of pure manure.