Does replacing chemical fertilizer with ryegrass (Lolium multiflorum Lam.) mitigate CH4 and N2O emissions and reduce global warming potential from paddy soil?

Abstract

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.