Reiner Wassmann

Impact of elevated temperatures on greenhouse gas emissions in rice systems: interaction with straw incorporation studied in a growth chamber experiment

AimsTwo pot experiments in a “walk-in” growth chamber with controlled day and night temperatures were conducted to investigate the influence of elevated temperatures along with rice straw incorporation on methane (CH4) and nitrous oxide (N2O) emissions as well as rice yield.MethodsThree temperature regimes–29/25, 32/25, and 35/30xa0°C (Exp. I) and 29/22, 32/25, and 35/28xa0°C (Exp. II), representing daily maxima/minima were used in the study. Two amounts of rice straw (0 and 6xa0txa0ha−1) were applied with four replications in each temperature regime. CH4 and N2O emissions as well as soil redox potential (Eh) were monitored weekly throughout the rice-growing period.ResultsElevated temperatures increased CH4 emission rates, with a more pronounced effect from flowering to maturity. The increase in emissions was further enhanced by incorporation of rice straw. A decrease in soil Eh to <−100xa0mV and CH4 emissions was observed early in rice straw–incorporated pots while the soil without straw did not reach negative Eh levels (Exp. I) or showed a delayed decrease (Exp. II). Moreover, soil with high organic C (Exp. II) had higher CH4 emissions. In contrast to CH4 emissions, N2O emissions were negligible during the rice-growing season. The global warming potential (GWP) was highest at high temperature with rice straw incorporation compared with low temperature without rice straw. On the other hand, the high temperature significantly increased spikelet sterility and reduced grain yield (pu2009<u20090.05).ConclusionsElevated temperature increased GWP while decreased rice yield. This suggests that global warming may result in a double negative effect: higher emissions and lower yields.

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.

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.

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.