INFLUENCE OF ORGANIC-MATTER INCORPORATION ON THE METHANE EMISSION FROM A WETLAND RICE FIELD

Methane (CH4) emission from Philippine rice paddies was monitored with a closed chamber technique during the 1992 dry and wet season. CH4 em issions were significantly higher in the dry season. Application of gr een manure stimulated CH4 emissions. In plots that received more than 11 t ha(-1) of fresh green manure, CH4 emission was highest during the first half of the growing season. Significant amounts of CH4 may evol ve during or immediately after transplanting, if the organic amendment s are incorporated 1 to 3 weeks before transplanting. Laboratory incub ations of soil cores show that CH4 production is highest near the soil surface. CH4 production in green manure treated fields is higher than in urea-fertilized fields, but toward the end of the season this diff erence is less pronounced. Around panicle initiation, the fraction of CH4, produced, which was emitted to the atmosphere, is lower than at t illering or ripening. The impact of organic amendments on CH4 emission s at different locations of the world can be described by a dose respo nse curve, if CH4 emission from organically amended plots is expressed relative to CH4 emission from mineral fertilized plots of the same lo cation and season Various organic amendments (e.g., straw, fermented r esidues) have a similar effect on CH4 emissions after correction for d ifferences in easily decomposable carbon content.