Application of raw animal manure to agricultural land has resulted in environmental and health problems. Alternatives, such as composting, are now being developed to alleviate this situation. However, very little information is available regarding the fate of composts when added to fine-textured and poorly drained soils, especially with respect to the initial decomposition of composts and their effects on soil-derived CO2 and N2O emissions. The Brookston clay loam (Orthic Humic Gleysol) from Ontario, Canada were used in this study. We evaluated food waste compost (FW), yard waste compost (YW), liquid pig manure (LPM), LPM+yard waste compost (PMY) and LPM+wheat straw compost (PMS). Red clover (Trifolium pratense) (RC) and an unamended control soil were also tested. The solid amendments were divided into ground and unground treatments. Carbon dioxide emissions were increased relative to the control soil for all treatments except PMY. Total CO2 emissions over the 144-h incubation from unground material followed the pattern (P<0.05): YW (849 mg CO2-C kg-1 soil)>RC (554 mg CO2-C kg-1 soil)>LPM (444 mg CO2-C kg-1 soil)>FW (203 mg CO2-C kg-1 soil)~PMS (194 mg CO2-C kg-1 soil)~PMY (157 mg CO2-C kg-1 soil). The RC, YW and PMS significantly increased N2O emissions compared to all other treatments and the control. Total N2O emissions from unground material over the 144-h incubation followed the pattern (P<0.05): RC~YW~PMS (1230-1490 micro g N2O-N kg-1 soil)>LPM~FW~PMY~Control (44-404 micro g N2O-N kg-1 soil). Grinding was found to increase CO2 emissions from YW, PMY, PMS, and N2O emissions from RC. The CO2 emissions were due primarily to amendment composition and not particle size, as the relative differences in CO2 emission among ground and unground treatments remained nearly constant. Carbon dioxide emissions from LPM were reduced substantially by composting the manure with yard waste (PMY).