Reducing methane (CH₄) emission from paddy rice production is an important target for many Asian countries in order to comply with their climate policy commitments. National greenhouse gas (GHG) inventory approaches like the Tier-2 approach of the Intergovernmental Panel on Climate Change (IPCC) are useful to assess country-scale emissions from the agricultural sector. In paddy rice, alternate wetting and drying (AWD) is a promising and well-studied water management technique which, as shown in experimental studies, can effectively reduce CH₄ emissions. However, so far little is known about GHG emission rates under AWD when the technique is fully controlled by farmers. This study assesses CH4 and nitrous oxide (N₂O) fluxes under continuous flooded (CF) and AWD treatments for seven subsequent seasons on farmers’ fields in a pumped irrigation system in Central Luzon, Philippines. Under AWD management, CH₄ emissions were substantially reduced (73% in dry season (DS), 21% in wet season (WS)). In all treatments, CH₄ is the major contributor to the total GHG emission and is, thus, identified as the driving force to the global warming potential (GWP). The contribution of N₂O emissions to the GWP was higher in CF than in AWD, however, these only offset 15% of the decrease in CH₄ emission and, therefore, did not jeopardize the strong reduction in the GWP. The study proves the feasibility of AWD under farmers’ management as well as the intended mitigation effect. Resulting from this study, it is recommended to incentivize dissemination strategies in order to improve the effectiveness of mitigation initiatives. A comparison of single CH₄ emissions to calculated emissions with the IPCC Tier-2 inventory approach identified that, although averaged values showed a sufficient degree of accuracy, fluctuations for single measurement points have high variation which limit the use of the method for field-level assessments.

Endophytic bacteria were isolated from the juice of a 6 month-old sugarcane cv. NiF-8, which was collected from Miyako, Okinawa and planted in a field lysimeter in Tsukuba, Ibaraki, Japan. The most probable number of N₂-fixing endophytes was 4.5 × 10⁵ cells per gram of fresh weight sample and 21 isolates have a positive reaction for ARA in an N₂-free semi-solid medium with 10% crystallized sugarcane sugar and 0.5% sugarcane juice. Analyses of some of the biochemical properties of the N₂-fixing isolates indicated that 13 isolates were putative strains of Acetobacter diazotrophicus, 4 isolates showed similar characteristics to those of Herbaspirillum seropedicae, and 4 isolates consisted of Herbaspirillum rubribalbicans-like strains. This study confirmed the existence of N₂-fixing endophytic bacteria in the Japanese sugarcane cv. NiF-8.

The high population of endophytic diazotrophs in the stalk of the Japanese sugarcane cultivar NiF-8 described in our previous report suggests the possible significant contribution of biological nitrogen fixation (BNF) to the crop nitrogen nutrition. To estimate the amount of BNF in this cultivar, the proportion of biologically fixed nitrogen (%Ndfa) to the plant total nitrogen uptake was determined by ¹⁵N dilution and natural ¹⁵N abundance (δ¹⁵N) techniques. Using the δ¹⁵N method, the estimated %Ndfa by the sugarcane cv. NiF-8 under field lysimeter conditions ranged from 32 to 38% at 6 months after planting (MAP) and from 27 to 34% at 7 MAP. With the ¹⁵N dilution method, the estimated %Ndfa by the sugarcane plants was 26.0% for the roots, 14.1% for the stem, and 20.5% for the leaves. These results indicate that the sugarcane cv. NiF-8 obtained part of its nitrogen requirements from BNF.