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SUMMARYIndex terms: greenhouse gas, flooding irrigation, intermittent irrigation, redox potential.(

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SUMMARYWinter cover crops are sources of C and N in flooded rice production systems, but very little is known about the effect of crop residue management and quality on soil methane (CH 4 ) and nitrous oxide (N 2 O) emissions. This study was conducted in pots in a greenhouse to evaluate the influence of crop residue management (incorporated into the soil or left on the soil surface) and the type of cover-crop residues (ryegrass and serradella) on CH 4 and N 2 O emissions from a flooded Albaqualf soil cultivated with rice (Oryza sativa L.). The closed chamber technique was used for air sampling and the CH 4 and N 2 O concentrations were analyzed by gas chromatography. Soil solution was sampled at two soil depths (2 and 20 cm), simultaneously to air sampling, and the contents of dissolved organic C (DOC), NO 3 -, NH 4 + , Mn 2+ , and Fe 2+ were analyzed. Methane and N 2 O emissions from the soil where crop residues had been left on the surface were lower than from soil with incorporated residues. The type of crop residue had no effect on the CH 4 emissions, while higher N 2 O emissions were observed from serradella (leguminous) than from ryegrass, but only when the residues were left on the soil surface. The more intense soil reduction verified in the deeper soil layer (20 cm), as evidenced by higher contents of reduced metal species (Mn 2+ and Fe 2+ ), and the close relationship between CH 4 emission and the DOC contents in the deeper layer indicated that the sub-surface layer was the main CH 4 source of the flooded soil with incorporated crop residues. The adoption of management strategies in which crop residues are left on the soil surface is crucial to minimize soil CH 4 and N 2 O emissions from irrigated rice fields. In these production systems, CH 4 accounts (1)