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Remogna for their technical assistance. We also extend our appreciation to the anonymous reviewers who provided useful suggestions for improvement of this paper. This publication is the result of a FISR project funded by the Italian Ministry of Agriculture and Forestry. 1Mitigating the impact of fertilization on global warming: can leguminous green manure and compost help to reduce N 2 O and CO 2 emissions? ABSTRACT Alternative nitrogen fertilizers that stimulate low greenhouse gas emissions from soil are needed to reduce the impact of agriculture on global warming. Corn (Zea mais, L.) grown in a calcareous silt loam soil in northwestern Italy was fertilized with a municipal solid waste compost and vetch green manure (Vicia villosa, Roth.). Their potential to reduce N 2 O and CO 2 emissions was compared to that of urea (130 kg N ha -1 ). Gaseous fluxes were measured for two years in the spring (after soil incorporation of fertilizers) and in summer. In spring, the slow mineralization of compost reduced N 2 O emissions (0.11 % of supplied N) relative to urea (3.4 % of applied N), without an increase in CO 2 fluxes. Nitrous oxide (2.31 % of fixed N) and CO 2 emissions from rapid vetch decomposition did not differ from urea. When N 2 O and CO 2 fluxes were combined, compost reduced by 49% the CO 2 equivalent emitted following urea application. Vetch did not show such an effect. In summer, no fertilizer effect was found on N 2 O and CO 2 emissions. Compost proved to be potentially suitable to reduce CO 2 equivalent emitted after soil incorporation while vetch did not.For a thorough evaluation, net greenhouse gas emissions assessment should be extended to the entire N life cycle. Differences between calculated N 2 O emission factors and the default Tier 1 IPCC value (1%) confirmed the need for site-and fertilizer-specific estimations.Abbreviations: ΔCO 2 eq, increase of emitted CO 2 equivalent due to the applied fertilizer N respect to absence of fertilization; COM, fertilization with compost; CK, check plots not fertilized with N; EF, nitrous oxide emission factor of fertilizer N applied; GHG, greenhouse gas; LGM, fertilization with a leguminous green manure (hairy vetch); Ndfa, N derived from the atmosphere and fixed by a legume; PD, potential denitrification; PMN, N potentially mineralizable in anaerobiosis; SOC, soil organic carbon; SON, soil organic nitrogen; UR, fertilization with urea; WFPS, water-filled pore space.

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