Estimating denitrification from tall fescue fields irrigated with municipal wastewater Wastewater irrigation systems are designed to optimize crop fertility without promoting nitrate leaching. Land-based wastewater disposal systems lose atmospheric N via denitrification and ammonia volatilization with denitrification contributing proportionately more to total N losses especially when nitrate-dominated wastewater is used. Standard design procedures for land-based wastewater disposal assume 15 – 25% of the applied total N is lost to the atmosphere and/or is stored in the soil. However, few studies have attempted to verify actual N losses when nitrate-dominated wastewater is irrigated. The goal of this study was to quantify atmospheric N losses of the applied secondary treated wastewater N (~ 60-80% nitrate N) at the Pennsylvania State University Living Filter (LF) site. Wastewater is applied at a rate of 5 cm wk-1 throughout the year. Due to the high spatial and temporal variability of denitrification in terrestrial systems, in addition to measuring denitrification from intact soil cores using the acetylene inhibition method, we also simulated denitrification as N2O, NO and N2 using the DeNitrification DeComposition (DNDC) biogeochemical model. Preliminary results suggest that less than 15% of the applied wastewater total N or nitrate is lost via denitrification.