Effects of sulfadiazine-contaminated fresh and stored manure on a soil microbial community

The response of soil microorganisms to manure contaminated by veterinary antibiotics is not well understood. Therefore, a 57-d incubation experiment was performed to investigate effects of sulfadiazine (SDZ) contaminated manure on soil microorganisms. Manure was either obtained directly from medicated pigs or subsequently stored for six month. We hypothesized that SDZ-contaminated manure changes functions and structural composition of soil microorganisms and that manure storage reduces antibiotic effects. Rates of potential nitrification and N mineralization as well as PLFA (phospholipid fatty acid) patterns were determined. Addition of uncontaminated manure to soil affected N cycle processes and the microbial community structure, and effects differed between fresh and stored manure. The rates of potential nitrification, ammonification and N mineralization and ratios of bacteria/fungi and gram-negative/gram-positive bacteria derived from PLFA were lower in soil treated with stored compared to fresh, uncontaminated manure. SDZ-contaminated manure affected N cycle processes with slight differences due to manure storage, whereas PLFA(tot) and the derived bacteria/fungi ratio were only reduced by stored, contaminated manure. SDZ reduced rates of nitrification and N mineralization, while ammonification increased. Effects of SDZ on soil microorganisms were significant although the bioavailable SDZ fraction (CaCl2-extractable) rapidly declined. We conclude that conventional manure storage is unsuited to reduce risks from sulfonamide antibiotics in the soil environment. (C) 2010 Elsevier Masson SAS. All rights reserved.