Grass species have been shown to have differing greenhouse gas fluxes and annual soil carbon (C) accumulations.  However, little research has investigated the differences within species (i.e. cultivars) or the influence of mowing practices on greenhouse gas fluxes and annual soil C accumulations.  The objectives of this study were to 1) examine the greenhouse gas flux and labile soil C accumulation for tall fescue (Festuca arundinacea Schreb.) and Kentucky bluegrass (Poa pratensis L.) cultivars with varying leaf elongation rates and 2) evaluate the influence of collecting or returning clippings on labile soil C and the greenhouse gas flux.  Permanganate oxidizable C was used to evaluate labile soil C, and the vented-chamber method was used for greenhouse gas flux measurements.  Results from the first year of the trial will be discussed.