Effect of chicken manure containing enrofloxacin on soil respiration, microbial biomass, and population of some beneficial bacteria

The concentration of antibiotics in the soil increases with the addition of fresh or composed chicken manure containing antibiotics and may affect the microbial community of the soil. The purpose of this study was to evaluate the effect of adding enrofloxacin containing chicken manure to soil on the population of Azotobacter spp, Pseudomonas putida and Pseudomonas fluorescens, as well as microbial biomass and respiration of soil. An experiment was conducted in a laboratory for 45 days with 7 treatments and three replications including fresh and composted chicken manure containing enrofloxacin in two levels of high (26.2 mg kg-1) and low (4.23 mg kg-1) concentrations and manure without any antibiotic based on a completely randomized design. The results showed that the application of chicken manure containing enrofloxacin reduced the population of Azotobacter spp (28 percent), Pseudomonas fluorescens (73 percent) and Pseudomonas putida (14.6 percent) in the soils. However, the composting of chicken manure, although reducing its negative effect, still led to a decline in population. Application of fresh chicken manure led to a 127 percent increase in microbial respiration of the soil compared to control but between other treatments there was no meaningful difference. The use of chicken manure without antibiotic significantly increased the microbial biomass (95 percent). The presence of high concentration of enrofloxacin in poultry manure had a negative effect on the microbial biomass increase, especially at the beginning of the period.