ENVIRONMENTAL IMPLICATIONS OF THE LAND APPLICATION OF MANURE CONTAINING ANTIMICROBIALS TYLOSIN AND CHLORTETRACYCLINE

Antimicrobial and antibiotic compounds are used in therapeutic doses in the agricultural industry to prevent disease and at sub-therapeutic levels to enhance growth promotion and feed efficiency. These compounds are specifically designed to poorly adsorb into the gut of the animal, and as a result > 90% of the antibiotic parent compound can be excreted from the animal in a biologically-active form. The predominant pathway for these antibiotics to enter the environment is through land application of antibiotic-laden manure. The purpose of this research was to ascertain how land application of antimicrobial swine manure could impact soil-microbe interactions that naturally exist within common eastern South Dakota soils. The research consisted of two phases: soil-manure batch reactors and manure loading soil column experiments. The objective for the batch reactor experiments was to determine the impacts of CTC and tylosin containing manure on aerobic soil microbial respiration rates. For the soil column experiments, the objective was to determine whether and how CTC and tylosin containing manure affects the migration or transformation of essential crop nutrients nitrogen, phosphorous, and carbon within a simulated A soil horizon. Batch reactor experimental results indicated that soils amended with the tylosin manure reduced CO₂ production compared to CTC and no antimicrobial containing manures. Tylosin was further found to inhibit biological carbon mineralization within the soil columns at rates similar to the no manure control. CTC was found to have limited impacts on both aerobic respiration rates and nutrient transport and transformation within the soil columns, suggesting limited environmental implications exist for the land application of CTC containing manure within aerobic soils.