Bjoern Ole Sander

Appropriate frequency and time of day to measure methane emissions from an irrigated rice paddy in Japan using the manual closed chamber method

Rice agriculture is a large anthropogenic source of atmospheric methane (CH4). The reliable estimation of CH4 emissions requires frequent measurements to trace diurnal and seasonal variations. To evaluate the appropriate intervals and optimal time of day to measure CH4 emissions using the manual closed chamber method, this study analysed four datasets of CH4 fluxes in a Japanese irrigated rice paddy measured at 2-hour intervals using the automated closed chamber method. The typical diurnal variation in the CH4 flux was observed after the rices heading stage, during which the daily time-weighted mean CH4 flux was observed twice, in the 08:00–11:59 and 18:00–21:59 time windows. During the flooded rice-growing period, the CH4 emissions, which were estimated by weekly measurements once per day during the 10:00–11:59 time window, corresponded to 93–106% of the emissions calculated using the automated measurement method. In contrast, no regular measurement strategies produced a satisfactory estimate of the CH4 emissions during the non-flooded rice-growing period because of a sharp increase in the CH4 flux just after the drainage. Consequently, the combination of weekly measurements once per day at approximately 10:00 as local mean time for the flooded rice-growing period and daily measurements once per day during the daytime for 1 week after each drainage event is recommended as a strategy to obtain the estimation with a ±10% error.

Common practices for manual greenhouse gas sampling in rice production: a literature study on sampling modalities of the closed chamber method

Rice production is a major source of global methane emissions and many studies have been conducted to quantify flux rates of methane alongside N2O emissions from rice fields. The closed chamber method with manual sampling is the conventional approach for determining greenhouse gas (GHG) emission rates from rice fields. However, as of now, there is no commonly accepted standard for the measurement protocols, so that published studies encompass a variety of different modalities depending on the specific settings and labour limitations of a given study. This literature study comprises 155 peer-reviewed articles on manual GHG sampling with a static closed chamber as a basis to determine the most common practices of this method regarding the following features: (1) procedures (duration of chamber closure, number of gas samples per chamber closure and number of replicate chambers), (2) timing (number of samplings per day and time of day of sampling) and (3) intervals (between two consecutive sampling days).It has been found that some features show a high degree of uniformity among these studies, namely, the procedures. On the other hand, other features of the measuring protocol diverge widely (timing and intervals). Derived from these results, the following common practices (compiling features being applied in more than 66% of the studies that give information on the particular feature) have been identified: duration of chamber closure (30 minutes or less), number of gas samples per chamber closure (3 or 4), number of replicates (3), number of samplings per day (1 or 2), time of day of sampling (late morning) and interval (7 days or less).

Climate-Determined Suitability of the Water Saving Technology "Alternate Wetting and Drying" in Rice Systems: A Scalable Methodology demonstrated for a Province in the Philippines

70% of the world’s freshwater is used for irrigated agriculture and demand is expected to increase to meet future food security requirements. In Asia, rice accounts for the largest proportion of irrigated water use and reducing or conserving water in rice systems has been a long standing goal in agricultural research. The Alternate Wetting and Drying (AWD) technique has been developed to reduce water use by up to 30% compared to the continuously flooded conditions typically found in rice systems, while not impacting yield. AWD also reduces methane emissions produced by anaerobic archae and hence has applications for reducing water use and greenhouse gas emissions. Although AWD is being promoted across Asia, there have been no attempts to estimate the suitable area for this promising technology on a large scale. We present and demonstrate a spatial and temporal climate suitability assessment method for AWD that can be widely applied across rice systems in Asia. We use a simple water balance model and easily available spatial and temporal information on rice area, rice seasonality, rainfall, potential evapotranspiration and soil percolation rates to assess the suitable area per season. We apply the model to Cagayan province in the Philippines and conduct a sensitivity analysis to account for uncertainties in soil percolation and suitability classification. As expected, the entire dry season is climatically suitable for AWD for all scenarios. A further 60% of the wet season area is found suitable contradicting general perceptions that AWD would not be feasible in the wet season and showing that spatial and temporal assessments are necessary to explore the full potential of AWD.

Measuring GHG Emissions from Rice Production in Quang Nam Province (Central Vietnam): Emission Factors for Different Landscapes and Water Management Practices

This study comprises greenhouse gas (GHG) emission measurements on rice fields in the Vu Gia/Thu Bon Basin in Central Vietnam , as part of an interdisciplinary research project. The experiments were conducted in the delta lowland (DL) and hilly midland (HM), over three seasons (summer–autumn in 2011 and 2012; winter–spring season in 2012) with two water management treatments namely continuous flooding (CF) and alternate wetting and drying (AWD) . GHG emissions were dominated by methane (CH4) emissions showing large difference among seasons, whereas nitrous oxide (N2O) emissions were negligible and irrelevant in the overall carbon footprint . However, temporal patterns were not conclusive over the entire observation period. The observed seasonal CH4 emission rates ranging from 83 to 696 kg CH4 per ha were relatively higher compared to other field studies and can, at least in part, be attributed to organic amendments applied in accordance to farmers’ practice. The practice of AWD reduced CH4 emissions significantly (P < 0.0001) in all seasons, corresponding in average to 71 % of the emissions from CF. On the other hand, AWD had no significant effect on N2O emissions. The average seasonal CH4 emission in the DL (420 kg ha−1) was also significantly higher than in the HM (206 kg ha−1). Compared with IPCC default values, this data set from Vietnamese rice fields indicates a higher emission level and Scaling factor for AWD. The average grain yield across all sites and seasons increased by 4 % (P < 0.0002) relative to CF with the practice of AWD.

The effective mitigation of greenhouse gas emissions from rice paddies without compromising yield by early-season drainage

Global rice production systems face two opposing challenges: the need to increase production to accommodate the worlds growing population while simultaneously reducing greenhouse gas (GHG) emissions. Adaptations to drainage regimes are one of the most promising options for methane mitigation in rice production. Whereas several studies have focused on mid-season drainage (MD) to mitigate GHG emissions, early-season drainage (ED) varying in timing and duration has not been extensively studied. However, such ED periods could potentially be very effective since initial available C levels (and thereby the potential for methanogenesis) can be very high in paddy systems with rice straw incorporation. This study tested the effectiveness of seven drainage regimes varying in their timing and duration (combinations of ED and MD) to mitigate CH4 and N2O emissions in a 101-day growth chamber experiment. Emissions were considerably reduced by early-season drainage compared to both conventional continuous flooding (CF) and the MD drainage regime. The results suggest that ED+MD drainage may have the potential to reduce CH4 emissions and yield-scaled GWP by 85-90% compared to CF and by 75-77% compared to MD only. A combination of (short or long) ED drainage and one MD drainage episode was found to be the most effective in mitigating CH4 emissions without negatively affecting yield. In particular, compared with CF, the long early-season drainage treatments LE+SM and LE+LM significantly (p<0.01) decreased yield-scaled GWP by 85% and 87% respectively. This was associated with carbon being stabilised early in the season, thereby reducing available C for methanogenesis. Overall N2O emissions were small and not significantly affected by ED. It is concluded that ED+MD drainage might be an effective low-tech option for small-scale farmers to reduce GHG emissions and save water while maintaining yield.

Paddy soil drainage influences residue carbon contribution to methane emissions

Water drainage is an important mitigation option for reducing CH4 (methane) emissions from residue-amended paddy soils. Several studies have indicated a long-term reduction in CH4 emissions, even after re-flooding, suggesting that the mechanism goes beyond creating temporary oxidized conditions in the soil. In this pot trial, the effects of different drainage patterns on straw-derived CH4 and CO2 (carbon dioxide) emissions were compared to identify the balance between straw-carbon CH4 and CO2 emissions influenced by soil aeration over different periods, including effects of drainage on emissions during re-flooding. The water treatments included were: continuous flooding [C] as the control and five drainage patterns (pre-planting drainage [P], early-season drainage [E], midseason drainage [M], pre-planting plus midseason drainage [PM], early-season-plus-midseason drainage [EM]). An equal amount of 13C-enriched rice straw was applied to all treatments to identify straw-derived 13C-gas emissions from soil carbon derived emissions. The highest fluxes of CH4 and δ13C-CH4 were recorded from the control treatment in the first week after straw application. The CH4 flux and δ13C-CH4 were reduced the most (0.1-0.8 μg CH4 g-1 soil day-1 and -13 to -34‰) in the pre-planting and pre-planting plus midseason drainage treatments at day one after transplanting. Total and straw-derived CH4 emissions were reduced by 69% and 78% in pre-planting drainage and 77% and 87% in pre-planting plus midseason drainage respectively, compared to control. The early-season, midseason, pre-planting plus midseason and early-season-plus-midseason drainage treatments resulted in higher total and straw-derived CO2 emissions compared to the control and pre-planting drainage treatments. The pre-planting and pre-planting plus midseason drainage treatments lowered the global warming potential by 47-53%, and early-season and early-season-plus-midseason drainage treatments reduced it by 24-31% compared to control. By using labelled crop residues, this experiment demonstrates a direct link between early drainage and reduced CH4 emissions from incorporated crop residues, eventually leading to a reduction in total global warming potential. It is suggested that accelerated decomposition of the residues during early season drainage prolonged the reduction in CH4 emissions. Therefore, it is important to introduce the early drainage as an effective measure to mitigate CH4 emissions from crop residues.

Methane emission from rice cultivation in different agro-ecological zones of the Mekong river delta: seasonal patterns and emission factors for baseline water management

ABSTRACT 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 (EFz) in the context of the IPCC Tier 2 approach. The lowest EFz was computed for the saline accounting for 1.14 kg CH4 ha−1 d−1 (confidence interval: 0.60–2.14). The EFz 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 EFz 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.

Contribution of fallow periods between rice crops to seasonal GHG emissions: effect of water and tillage management

ABSTRACT Irrigated rice cultivation is a major source of greenhouse gas (GHG) emissions from agriculture. Methane (CH4) and nitrous oxide (N2O) are emitted not only throughout the growing season but also in the fallow period between crops. A study was conducted for two transition periods between rice crops (dry to wet season transition and wet to dry season transition) in the Philippines to investigate the effect of water and tillage management on CH4 and N2O emissions as well as on soil nitrate and ammonium. Management treatments between rice crops included (1) continuous flooding (F), (2) soil drying (D), (3) soil drying with aerobic tillage (D + T), and (4) soil drying and wetting (D + W). The static closed chamber method was used to measure CH4 and N2O fluxes. Soil nitrate accumulated and N2O was emitted in treatments with soil drying. Nitrate disappeared while ammonium gradually increased after the soil was flooded during land preparation, indicating net nitrogen mineralization. N2O emissions were highest in both transition periods in D + W (437 and 645 µg N2O m−2 h−1). Methane emissions were significant in only the F treatment. The highest global warming potential (GWP) in the transition between rice crops occurred in F, with CH4 contributing almost 100% to the GWP. The GWP from other treatments was lower than F, with about 60–99% of the GWP attributed to N2O emissions in treatments with soil drying. The GWP in the transition between rice crops represented up to 26% of the total GWP from harvest to harvest. This study demonstrates that the transition period can be an important source of GHG emissions with relative importance of CH4 and N2O depending on the soil water regime. Therefore, the transition period should not be disregarded when estimating GHG emissions for rice cropping systems.

Increasing sensitivity of methane emission measurements in rice through deployment of ‘closed chambers’ at nighttime

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.

Climate-based suitability assessment for alternate wetting and drying water management in the Philippines: a novel approach for mapping methane mitigation potential in rice production

ABSTRACT The ‘alternate wetting and drying’ (AWD) technology for rice is a water-saving technology with a high greenhouse gas (GHG) mitigation potential. The Philippine government attempts to disseminate AWD in all national irrigation systems in order to adapt to increasingly scarce water resources. This article describes how a model for climatic AWD suitability assessment developed by the International Rice Research Institute (IRRI) is suited for a national assessment of the Philippines, and country-scale climatic suitability maps for AWD are develop for wet and dry season. Furthermore, how the assessment can be used to estimate potential GHG emission savings is illustrated. Results show that a maximum of 60% of the rice area of the Philippines is climatically suited to AWD, reaching more than 90% in the dry and 34% in the wet season. The potential, maximum annual reduction is around 265,000t of CH4 emissions from lowland rice in the Philippines, or around 15% of the countrys annual emissions from the agriculture sector. The article concludes with recommendations on the use of this simple spatial water balance model for mitigation planning which offers a more spatially detailed, quantitative and transparent estimate of national GHG emissions in the rice sub-sector for rice producing countries.