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The incorporation of ryegrass (Lolium multi orum Lam.; RG), a winter grass manure, could partly replace chemical N and reduce N loss during the succeeding rice seasons, but little is known about its impact on greenhouse gas emission. This study investigated the effect of different RG-urea substitution ratios (0%, 25%, 50%, 75% and 100%) on C and N release, CH 4 and N 2 O emissions in a paddy soil.(Methods) Gas samples for CH 4 and N 2 O uxes measurement were collected by using a closed chamber and determined by chromatograph method. C and N release from the incorporated RG residue were tested by a mesh bag method.(Results) C and N release from RG followed a single exponential decay model, with 95.5%-97.8% of the original C and 98.7%-99.3% of N released during 192 days. RG-urea substitution ratio increased CH 4 emission, but was negatively correlated with N 2 O emission. In comparison with 0% substitution, global warming potential (GWP) and greenhouse gas intensity (GHGI) were not signi cantly different for the 25% and 50% RG substitutions, but were signi cantly higher for the 75% and 100% substitutions (P<0.05). Soil redox, C and N remaining in litter residue were key characteristics explaining CH 4 emission, while NH 4 + -N and NO 3 --N concentrations were correlated with the variation of N 2 O emission. (Conclusion)The increased CH 4 emission by RG incorporation could be offset by the reduced N 2 O emission when RGurea substitution ratio was 50% or less.

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