This study comprises a set of methane emission measurements in rice fields located in the four agro-ecological zones of the Mekong River Delta (MRD), namely the zones with (i) alluvial soils, (ii) salinity intrusion, (iii) deep flood, and (iv) acid sulfate soils. These zones have very distinct bio-physical conditions and cropping cycles that will affect methane emissions in various forms. Our study includes comprehensive mapping of these zones as well as an overview of rice statistics (activity data) at provincial level for each cropping season. Emission data were obtained by the closed chamber method. The available data set comprises 7 sites with 15 cropping seasons. Mean emission rates showed large variations ranging from 0.31 to 9.14 kg CH₄ ha⁻¹ d⁻¹. Statistical analysis resulted in weighted means for all zones that we use as zone-specific CH₄ emission factors (EF_z) in the context of the IPCC Tier 2 approach. The lowest EF_z was computed for the saline accounting for 1.14 kg CH₄ ha⁻¹ d⁻¹ (confidence interval: 0.60–2.14). The EF_z values of the alluvial and acid sulfate zones were 2.39 kg CH₄ ha⁻¹ d⁻¹ (2.19–4.13) and 2.78 kg CH₄ ha⁻¹ d⁻¹ (2.65–3.76), respectively, which indicated that they were not different from each other derived from their confidence intervals. The deep flood zone, however, required a season-specific, assessment of EF_z because emission in the autumn–winter cropping season, corresponding to the wet period, was significantly higher (9.14 kg CH₄ ha⁻¹ d⁻¹ (7.08–11.2)) than the other seasons (2.24 kg CH₄ ha⁻¹ d⁻¹ (1.59–3.47)). Although these emission factors correspond to baseline water management and do not capture the diversity of farmers’ practices, we see the availability of zone-specific data as an important step for a more detailed assessment of Business as Usual emissions as well as possible mitigation potentials in one of the most important rice growing regions of the world.

This paper examines how rice farmers at all gender and ages perceive climate change and adopt Climate Smart Agriculture (CSA) technologies to enhance resilience and adaptation in three sub-regions of Vietnam. Impacts on livelihoods resilience, workloads of left behind family members, gender roles and responsibilities are also assessed. Using data from 579 randomly-sampled households, results show that women play a more important role in rice production in North and Central compared to the South due to higher rate of male out-migration. Differences in awareness and adoption of CSA technologies are observed although men and women across provinces have similar perception of climate change. The key challenges of youth engagement include drudgery in farm operations, labour-intensive technologies, low profit, inadequate access to land and credit, and lack of agricultural insurance scheme. Results imply that farmers should be provided with equal opportunities in trainings and field demonstrations on CSA technologies. Recommendations to attract the youth include: (i) promote on-farm training at school; (ii) organize exchange visits, trade fairs, competition on farming techniques; (iii) develop good production and business model; (iv) emphasize the important role of farmers and agriculture; (v) update agricultural policies and programmes; (vi) upgrade the skills and knowledge of extension workers.

This study comprises field experiments on methane emissions from rice fields conducted with an Eddy-Covariance (EC) system as well as test runs for a modified closed chamber approach based on measurements at nighttime. The EC data set covers 4 cropping seasons with highly resolved emission rates (raw data in 10 Hz frequency have been aggregated to 30-min records). The diel patterns were very pronounced in the two dry seasons with peak emissions at early afternoon and low emissions at nighttime. These diel patterns were observed at all growing stages of the dry seasons. In the two wet seasons, the diel patterns were only visible during the vegetative stages while emission rates during reproductive and ripening stages remained within a fairly steady range and did not show any diel patterns. In totality, however, the data set revealed a very strong linear relationship between nocturnal emissions (12-h periods) and the full 24-h periods resulting in an R²-value of 0.8419 for all data points. In the second experiment, we conducted test runs for chamber measurements at nighttime with much longer deployment times (6 h) as compared to measurements at daylight (typically for 30 min). Conducting chamber measurements at nighttime excluded drastic changes of temperatures and CO₂ concentrations. The data also shows that increases in CH₄ concentrations remained on linear trajectory over a 6h period at night. While end CH₄ concentrations were consistently >3.5 ppm, this long-term enclosure represents a very robust approach to quantify emissions as compared to assessing short-term concentration increases over time near the analytical detection limit. Finally, we have discussed the potential applications of this new approach that would allow emission measurements even when conventional (daytime) measurements will not be suitable. Nighttime chamber measurements offer an alternative to conventional (daytime) measurements if either (i) baseline emissions are at a very low level, (ii) differences of tested crop treatments or varieties are very small or (iii) the objective is to screen a large number of rice varieties for taking advantage of progress in genome sequencing.

In this study, we developed user-friendly software (CF-Rice) for calculating the carbon footprints (CF) of rice products. The approach follows the principles of Life Cycle Assessment while incorporating more flexibility for activities specific to rice production. The graphical user interface provides empirical emission and conversion factors obtained from the literature and from primary research studies of rice value chains. CF-Rice also allows the entering of new values for specific processes or practices. Data outputs distinguish among the contributions of individual stages of the value chain as well as different greenhouse gases (GHG), namely, CH₄, N₂O and CO₂. The new tool was then applied to a scenario assessment of rice production in the regional context of Southeast Asia. The CF baseline of a typical rice value chain in the region accounted for a value of around 2300 g CO₂e/kg_Prod. The CF can be reduced by about 27.4% through water-saving practices alone and can further be reduced up to 37.3% through interventions that increase product recovery rates and, thus, reduce food losses. In contrast, straw incorporation into the soil increased the CF by 26.0%. The tool is well suited for impact assessments of advanced practices and technologies of rice value chains.

The new GHG calculator named SECTOR (Source-selective and Emission-adjusted GHG CalculaTOR for Cropland) is based on the IPCC Tier 2 approach for rice as well as other crops. The new features of SECTOR facilitate high flexibility in terms of entering newly obtained emission factors, easy data transfer from crop statistics for entering activity data and detailed specifications of GHG scenarios. A new procedure of entering frequency-based data on current water management practices was also developed. Moreover, the tool allows deviating from the 2006 IPCC Guidelines by considering field records with high background levels of N₂O emissions in the overall assessment of GHG emissions. This article assesses different applications of the tool, namely as add-ons to field measurements, for GHG calculation at national/sectorial scale and within measurement, reporting and verification of development projects. SECTOR is downloadable in the form of templates that can be used to develop custom versions with varying levels of disaggregated data entries at different scales. A case study for rice production in one Vietnamese province demonstrates the potential to display GHG results in combination with GIS. SECTOR can easily be adjusted to incorporate new emission factors and calculation procedures expected in forthcoming revisions of the IPCC Guidelines.