Direct greenhouse gas field emissions in dry-season rice farming in the Philippines via gas-chamber experiment: straw management evaluation and IPCC tier 1 emission comparison

Abstract Rice is a staple food in the Philippines, and its cultivation is a major source of greenhouse gas (GHG) emissions, particularly methane (CH₄) and nitrous oxide (N 2 O), from direct field emissions, making emission management in rice fields a key area for supporting national GHG reduction strategies. This study utilized a direct field gas chamber experiment in Victoria, Laguna, Philippines, during the dry season to determine how the removal of rice straw affects the direct field emissions from rice farming. Emissions including methane (CH 4 ), nitrous oxide (N 2 O), and carbon dioxide (CO 2 ) across every phase of rice production, from initial land preparation to the post-harvest period were continuously monitored. The study specifically evaluated two contrasting methods of straw management: leaving the straw in the soil, known as incorporation, and completely taking the straw away, defined as removal. The study’s results alligned with the core assumption that removing rice straw would reduce direct field emissions due to the limitation of available carbon and nitrogen in the soil, which, in turn, limits the key microbial processes that drive the production and release of these greenhouse gases. This was clearly demonstrated by the experimental results wherein straw incorporation led to a positive cumulative emission of 3.00 tons of CO 2 /ha while, conversely, straw removal generated net negative emissions of -3.19 tons of CO 2 /ha. Moreover, these findings provide robust, country-specific emission data for the Philippines, offering a significantly more accurate estimate of field emissions compared to the generalized factors used in the IPCC Tier 1 method.