Kazunori Minamikawa

Potential of prolonged midseason drainage for reducing methane emission from rice paddies in Japan: a long-term simulation using the DNDC-Rice model

Water management practices, such as midseason drainage (MD) and intermittent irrigation, are effective in reducing methane (CH4) emission from irrigated rice paddies. In a previous study in which two-year field experiments were conducted at nine sites across Japan, prolonged MD was found to reduce the seasonal total CH4 emission by 30.5u2009±u20096.7xa0% (meanu2009±u200995xa0% confidence interval) compared with conventional MD without compromising rice grain yield. However, the degree of CH4 reduction by water management is dependent on prevailing weather conditions. To estimate the mean effect of prolonged MD on CH4 emission at the nine sites with rice straw application, we conducted a long-term (20xa0years) simulation using a process-based biogeochemistry model, the DNDC-Rice. The model adjusted using site-specific parameters was able to reproduce the measured magnitude of the total CH4 emission and the suppressive effect of prolonged MD. The number of nonrainy days during MD explained the degree of CH4 reduction for each site and all sites combined. In the simulation, mean reduction percentage was 20.1u2009±u20095.6xa0% when acceptable prolonged MD (i.e., having less than 15xa0% yield loss) was applied compared with conventional MD. The discrepancy of the percentage between measurement and simulation was primarily attributable to longer nonrainy days during prolonged MD at several sites in the measurement than the mean of 20-year simulation. We therefore conclude that the long-term simulation better represents the mean reduction percentage of CH4 emission by prolonged MD relative to conventional MD at the nine sites across Japan.

Prediction of future methane emission from irrigated rice paddies in central Thailand under different water management practices.

There is concern about positive feedbacks between climate change and methane (CH4) emission from rice paddies. However, appropriate water management may mitigate the problem. We tested this hypothesis at six field sites in central Thailand, where the irrigated area is rapidly increasing. We used DNDC-Rice, a process-based biogeochemistry model adjusted based on rice growth data at each site to simulate CH4 emission from a rice-rice double cropping system from 2001 to 2060. Future climate change scenarios consisting of four representative concentration pathways (RCPs) and seven global climate models were generated by statistical downscaling. We then simulated CH4 emission in three water management practices: continuous flooding (CF), single aeration (SA), and multiple aeration (MA). The adjusted model reproduced the observed rice yield and CH4 emission well at each site. The simulated CH4 emissions in CF from 2051 to 2060 were 5.3 to 7.8%, 9.6 to 16.0%, 7.3 to 18.0%, and 13.6 to 19.0% higher than those from 2001 to 2010 in RCPs 2.6, 4.5, 6.0, and 8.5, respectively, at the six sites. Regionally, SA and MA mitigated CH4 emission by 21.9 to 22.9% and 53.5 to 55.2%, respectively, relative to CF among the four RCPs. These mitigation potentials by SA and MA were comparable to those from 2001 to 2010. Our results indicate that climate change in the next several decades will not attenuate the quantitative effect of water management practices on mitigating CH4 emission from irrigated rice paddies in central Thailand.

Impacts of alternate wetting and drying on greenhouse gas emission from paddy field in Central Vietnam

ABSTRACT Vietnam is the world’s fifth largest rice producing country. Since methane (CH4), a potent greenhouse gas (GHG), emission from the rice cultivation accounts for 14.6% of the national anthropogenic GHG emission, developing and disseminating mitigation options are the urgent need. Alternate wetting and drying (AWD) is the irrigation technique, in which a paddy field encompasses several soil-drying phases during the growth period, thereby reducing the CH4 emission. However, field trials of the AWD’s feasibility in Central Vietnam are limited so far. We therefore carried out a 3-year experiment in a farmer’s field both in winter–spring season and summer–autumn season. CH4 and nitrous oxide (N2O) emissions were compared among the three treatments of water management: continuous flooding (CF), AWD, and site-specific AWD (AWDS) that changed the degree of soil drying depending on the growth stage. The total water use including irrigation and rainfall was significantly (p < 0.05) reduced by AWD (by 15%) and AWDS (by 14%) compared to CF, but rice grain yield did not differ among the three treatments. The seasonal cumulative CH4 emission was significantly reduced by AWD (26%) and AWDS (26%) compared to CF, whereas the seasonal cumulative N2O emission did not differ among treatments. The resultant global warming potentials (GWPs) of CH4 and N2O under AWD and AWDS were 26% and 29% smaller than that under CF, respectively. The GWP of N2O was only 0.8% of the total GWP of CH4 + N2O. The yield-scaled GWP and water productivity (i.e., the ratio of grain yield to water use) were also improved by AWD and AWDS. No significant differences in the measured items between AWD and AWDS were attributed to similar variation patterns in the surface water level. The results confirm the AWD’s performance as a mitigation option for paddy GHG emission in Central Vietnam.

Alternate wetting and drying reduces methane emission from a rice paddy in Central Java, Indonesia without yield loss

ABSTRACT Water regimes play a central role in regulating methane (CH4) and nitrous oxide (N2O) emissions from irrigated rice field. Alternate wetting and drying (AWD) is a possible option, but there is limited information on its feasibility under local environmental conditions, especially for tropical region. We therefore carried out a 3-year experiment in a paddy field in Central Java, Indonesia to investigate the feasibility of AWD in terms of rice productivity, greenhouse gas (GHG) emission, and water use both in wet and dry seasons (WS and DS). The treatments of water management were (1) continuous flooding (CF), (2) flooding every when surface water level naturally declines to 15 cm below the soil surface (AWD), and (3) site-specific AWD with different criteria of soil drying (AWDS) established to find out the optimum for GHG emission reduction. Gas flux measurement was conducted by a static closed chamber method. Rice growth was generally normal and the grain yield did not significantly differ among the three treatments both in WS and DS. AWD and AWDS significantly reduced the total water use (irrigation + rainfall) as compared to CF. As expected, the seasonal total CH4 emission was significantly reduced by AWD and AWDS. On average, the CH4 emissions under AWD and AWDS were 35 and 38%, respectively, smaller than those under CF. It should be noted that AWD and AWDS were effective even in WS due partly to the field location on inland, upland area that facilitates the drainage. The seasonal total N2O emission did not significantly differ among the treatments. The results indicate that AWD is a promising option to reduce GHG emission, as well as water use without sacrificing rice productivity in this field.

Effects of alternate wetting and drying technique on greenhouse gas emissions from irrigated rice paddy in Central Luzon, Philippines

ABSTRACT Alternate wetting and drying (AWD) technique has been widely reported to reduce methane (CH4) emission from irrigated rice paddies. However, little is known about its feasibility in an environment that has distinct weather conditions involving tropical wet season (WS). To investigate the AWD’s feasibility in terms of reducing greenhouse gas (GHG) emissions both in dry season (DS) and WS, 3-year field experiments were conducted in Central Luzon, Philippines. Three treatments of water management were continuous flooding (CF), flooding when surface water level naturally declines to 15 cm below the soil surface (AWD), and site-specific AWD that modified the criteria of soil drying (AWDS). Methane and nitrous oxide (N2O) fluxes were measured using a closed chamber method, and the global warming potential (GWP) of the two GHGs was calculated. Rice grain yield did not significantly differ among treatments. In accordance with the previous findings, the seasonal total CH4 emission was significantly greater in WS than in DS. The effect of treatment was significant, but the reduction rate by AWD was just 1.7% compared to CF. The seasonal total N2O emission was significantly affected by cropping season and treatment. The AWD increased the N2O emission by 97%, especially in DS. The resultant GWP did not significantly differ among three treatments. The results indicate that the AWD and AWDS with the current settings were insufficient to reduce the annual GHG emissions in this site. However, fragmentary results obtained in the last DS suggest that an earlier rice residue incorporation and keeping dry soil conditions in the preceding fallow season is effective in reducing CH4 emission in combination with an earlier implementation of AWD.

Evaluating the effects of alternate wetting and drying (AWD) on methane and nitrous oxide emissions from a paddy field in Thailand

ABSTRACT Alternate wetting and drying (AWD) is a water-saving irrigation technique in a paddy field that can reduce the emission of methane, a potent greenhouse gas (GHG). It is being adopted to Asian countries, but different results are reported in literatures on methane, nitrous oxide emission, and rice productivity under AWD. Therefore, the local feasibility needs to be investigated before its adoption by farmers. The current study carried out a 3-year experiment in an acid sulfate paddy field in Prachin Buri, Thailand. During five crops (3 dry and 2 wet seasons), three treatments of water management were compared: continuous flooding (CF), flooding whenever surface water level declined to 15 cm below the soil surface (AWD), and site-specific AWD (AWDS) that weakened the criteria of soil drying (AWDS). Methane and nitrous oxide emissions were measured by a closed chamber method. Rice grain yield did not significantly (p < 0.05) differ among the three treatments. The amount of total water use (irrigation + rainfall) was significantly reduced by AWD (by 42%) and AWDS (by 34%) compared to CF. There was a significant effect of treatment on the seasonal total methane emission; the mean methane emission in AWD was 49% smaller than that in CF. The seasonal total nitrous oxide emission and the global warming potential (GWP) of methane and nitrous oxide did not differ among treatments. The contribution of nitrous oxide to the GWP ranged 39–62% among three treatments in dry season whereas 3–13% in wet season. The results indicate that AWD is feasible in terms of GHG emission mitigation, rice productivity, and water saving in this site, especially in dry season.

Site-specific feasibility of alternate wetting and drying as a greenhouse gas mitigation option in irrigated rice fields in Southeast Asia: a synthesis

ABSTRACT This study comprises a comprehensive assessment, integration, and synthesis of data gathered from a 3-year field experiment conducted at four sites in Southeast Asia, namely Hue, Vietnam; Jakenan, Indonesia; Prachin Buri, Thailand; and Muñoz, Philippines, to assess the site-specific feasibility of alternate wetting and drying (AWD) as a greenhouse gas (GHG) mitigation option in irrigated rice fields. AWD effectively reduced water use compared to continuous flooding (CF) but did not significantly reduce rice grain yield and soil carbon content in all sites. Methane (CH4) emissions varied significantly among sites and seasons as affected by soil properties and water management. AWD reduced CH4 emissions relative to CF by 151 (25%), 166 (37%), 9 (31%), and 22 (32%) kg CH4 ha−1 season−1 in Hue, Jakenan, Prachin Buri, and Muñoz, respectively. In Prachin Buri and Muñoz, AWD reduced CH4 emissions only during the dry season. Site-specific CH4 emission factors (EFs) ranged 0.13–4.50 and 0.08–4.88 kg CH4 ha−1 d−1 under CF and AWD, respectively. The mean AWD scaling factors (SFs) was 0.69 (95% confidence interval: 0.61–0.77), which is slightly higher than the Intergovernmental Panel on Climate Change (IPCC)’ SF for multiple aeration of 0.52 (error range: 0.41–0.66). Significant reductions in the global warming potential (GWP) of CH4+nitrous oxide (N2O) by AWD were observed in Hue and Jakenan (27.8 and 36.1%, respectively), where the contributions of N2O to the total GWP were only 0.8 and 3.5%, respectively. In Muñoz, however, CH4 emission reduction through AWD was offset by the increase in N2O emissions. The results indicate that the IPCC’s SF for multiple aeration may only be applied to irrigated rice fields where surface water level is controllable for a substantial period. This study underscores the importance of practical feasibility and appropriate timing of water management in successful GHG reductions by AWD.

Intercontinental comparison of greenhouse gas emissions from irrigated rice fields under feasible water management practices: Brazil and Japan

ABSTRACT Flooded rice fields are a significant anthropogenic source of methane (CH4) and nitrous oxide (N2O) from agriculture in Asia, Latin America, and the Caribbean regions. In this work, we comparatively assessed the potential of intermittent irrigation and continuous rice flooding for reducing soil CH4 and N2O emissions, partial global warming potential (pGWP), and its yield-scaled version (YpGWP) in northwestern Japan and southern Brazil. Seasonal CH4 emissions under continuous flooded soils were slight higher in Japan (738 ± 87 kg ha−1) than in Brazil (623 ± 197 kg ha−1), and they were probably related to the higher level of soil organic C and the longer period under flooding in the seedling transplanting system in the Japanese site. Intermittent irrigation had similar efficiency in decreasing soil CH4 emissions in both study areas, with the maximum mitigation potential of 71% in northwestern Japan and of 62% in southern Brazil. No significant difference in seasonal soil N2O emissions (−0.17 ± 0.05 to −0.24 ± 0.06 kg N2O ha−1 in Japan and 0.32 ± 0.08–1.16 ± 0.40 kg ha−1 in Brazil) or rice yield (7328–8064 kg ha−1 in Japan and 9391–10,231 kg ha−1 in Brazil) between irrigation systems was observed in either area. The potential of intermittent irrigation for reducing pGWP was around three times higher than that of continuous flooding in both sites. Thus, a reduction by 47–63% and 62–80% in yield-scaled pGWP was observed in southern Brazil and northwestern Japan, respectively. Like the well-established labor-intensive rice transplanting systems used in Asia, the introduction of feasible irrigation suppression systems in mechanized direct seeding rice fields in southern Brazil and other countries of Latin America and the Caribbean region is an effective choice for reducing greenhouse gas emissions with no adverse impact on rice yield.