2005 Annual Report 4d.Progress report. 4. This report serves to document research conducted under a specific cooperative research agreement between USDA and University of California. Additional details of research can be found in the report for the parent project 5310-12130-007-00-D. D. The degradation kinetics of sulfadimethoxine, a widely used sulfonamide antibiotic, in manure under aerobic condition was investigated. Based on an analysis of the first-order kinetics, and the assumption of the availability of sulfadimethoxine in manure for the degradation process, a new kinetic model was developed and was found to fit the degradation kinetics well. The degradation in sterilized manure is remarkably lower than that in non-sterilized manure, indicating that the microorganisms are responsible for the major degradation of this antibiotic in manure. In both non-sterilized and sterilized manure, the degradation rate constant decreases with the increasing initial concentration of sulfadimethoxine and the decrease rate in the non-sterilized manure is just slightly higher than that in the sterilized manure. This reveals that the decrease of the rate constant was caused mainly by the increasing adsorption of sulfadimethoxine in manure with the increase of the inhibition effect of sulfadimethoxine on the degrading microorganism is very limited. Increasing moisture and temperature greatly enhanced the degradation of sulfadimethoxine in the manure. Model calculation results showed that not only the degradation rate is increased but also the desorption process of sulfadimethoxine from manure particles is accelerated with the increasing moisture and temperature. Separated collecting of highly contaminated manure, keeping a high moisture of manure and storing at a mild warm place under aerobic condition can greatly enhance the degradation of sulfadimethoxine in manure, thus to effectively eliminate its contamination in the environment.