Simultaneous records of methane and nitrous oxide emissions in rice-based cropping systems under rainfed conditions uri icon

abstract

  • Rainfed rice (Oryza sativa L.)-based cropping systems are characterized by alternate wetting and drying cycles as monsoonal rains come and go. The potential for accumulation and denitrification of NO(3)(-) is high in these systems as is the production and emission of CH(4) during the monsoon rice season. Simultaneous measurements of CH(4) and N(2)O emissions using automated closed chamber methods have been reported in irrigated rice fields but not in rainfed rice systems. In this field study at the International Rice Research Institute, Philippines, simultaneous and continuous measurements of CH(4) and N(2)O were made from the 1994 wet season to the 1996 dry season. During the rice-growing seasons, CH(4) fluxes were observed, with the highest emissions being in organic residue-amended plots. Nitrous oxide fluxes, on the other hand, were generally nonexistent, except after fertilization events where low N(2)O fluxes were observed. Slow-release N fertilizer further reduced the already low N(2)O emissions compared with prilled urea in the first rice season. During the dry seasons, when the field was planted to the upland crops cowpea [Vigna unguiculata (L.) Walp] and wheat (Triticum aestivum L.), positive CH(4) fluxes were low and insignificant except after the imposition of a permanent flood where high CH(4) fluxes appeared. Evidences of CH(4) uptake were apparent in the first dry season, especially in cowpea plots, indicating that rainfed lowland rice soils can act as sink for CH(4) during the upland crop cycle. Large N(2)O fluxes were observed shortly after rainfall events due to denitrification of accumulated NO(3)(-). Cumulative CH(4) and N(2)O fluxes observed during this study in rainfed conditions were lower compared with previous studies on irrigated rice fields.

publication date

  • 2000
  • 2000