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Methane emissions from major rice ecosystemsMETHANE EMISSIONS FROM MAJOR RICE ECOSYSTEMS A joint publication of IRRI and Kluwer Academic Publishers Edited by R. Wassmann, R.S. Lantin, H.-U. Neue Modeling rice-plant-mediated methane emission J.R.M. Arah and G.J.D. Kirk Late-season methane emissions from flooded ricefields appear to be fuelled by root exudation and death, and to be transmitted to the atmosphere largely through the plant. We present a general transport-reaction model which accommodates these phenomena, together with a simplified ("cartoon") version intended to reproduce the salient features of most plant-dominated methane-emitting systems. Our cartoon model is capable of reproducing measured concentration profiles and fluxes. Sensitivity analysis suggests that cultivars with high specific root transmissivity may, other things being equal, reduce rather than enhance net emission. Simulations assuming exponential growth of the root system followed by Gaussian die-back resemble measured flux trajectories, and also point to great variability in the fraction of methane oxidised before it reaches the atmosphere. Air-entry on drainage reduces simulated methane fluxes and the fractions of those fluxes mediated by plants. It also increases the fraction of methane oxidised. W. Cheng, K. Chander, and K. Inubushi Incubation experiments were conducted under controlled laboratory conditions to study the interactive effects of elevated carbon dioxide (CO2) and temperature on the production and emission of methane (CH4) from a submerged paddy soil microcosm. Soil samples (unamended soil; soil + straw; soil + straw + N fertilizer) were placed in four growth chambers specifically designed for a combination of two levels of temperature (25 oC or 35 oC) and two levels of CO2 concentration (400 µmol mol-1 or 800 µmol mol-1) with light intensity of about 3000 Lx for 16 h d-1. At 7, 15, 30, and 45 d after incubation, CH4 flux, CH4 dissolved in flood water, subsurface soil-entrapped CH4, and CH4 production potential of the subsurface soil were determined. The results are summarized as follows: 1) The amendment with rice straw led to a severalfold increase in CH4 emission rates, especially at 35 oC. However, the CH4 flux tended to decrease considerably after 15 d of incubation under elevated CO2. 2) The amount of entrapped CH4 in subsurface soil and the CH4 production potential of the subsurface soil were appreciably larger in the soil samples incubated under elevated CO2 and temperature during early incubation period. However, after 15 d, they were similar in the soil samples incubated under elevated or ambient CO2 levels. These results clearly indicated that elevated CO2 and temperature accelerated CH4 formation by the addition of rice straw, while elevated CO2 reduced CH4 emission at both temperatures. M.S. Aulakh, J. Bodenbender, R. Wassmann, and H. Rennenberg A major portion (60 -90 %) of the methane (CH4) emitted from rice fields to the atmosphere is transported through the aerenchyma of the rice plants. However, a rapid and accurate method to study the CH4 transport capacity (MTC) of rice plants is not available. We developed a gas sampling and analytical device based on a closed 2-compartment chamber technique and analyzed the enrichment of the CH4 mixing ratio inside the shoot-compartment of cylindrical cuvettes enclosing individual rice plants under ambient conditions. The computer-controlled analytical system consists of a gas chromatograph (GC), and a pressure controlled autosampler for 8 cuvettes (7 for plants and one for CH4-calibration gas). The system automates closure and opening of plant cuvettes using pneumatic pressure, air sample collection and injection into the GC, and CH4 analysis. It minimizes sources of error during air sampling by continuously mixing headspace air of each cuvette, maintaining pressure and composition of the headspace inside the cuvettes, purging the dead volumes between the sampler induction tube and GC, and running a reference CH4-calibration gas sample in each cycle. Tests showed that the automated system is a useful tool for accurate sampling of headspace-air of cylindrical cuvettes enclosing individual rice plants, and enables the rapid and accurate fully automated analysis of CH4 in the headspace air samples. A linear relationship was obtained between CH4 transported by rice plants of two cultivars (IR72, a high yielding dwarf, and Dular, a traditional tall cultivar) and concentration of CH4 up to 7500 ppm used for purging the nutrient culture solution surrounding the roots in the root-compartment of the chamber. Further increase in CH4 emission by shoots was not observed at 10000 ppm CH4 concentration in the root-compartment of the chamber. MTC of rice plants of IR72 measured at six development stages showed that MTC was lowest at seedling stage and increased gradually until panicle initiation, no further change at flowering, but marked decrease at maturity. These results suggest that the plants have 45 to 246 % greater potentials to transport CH4 than the highest CH4 emission rates reported under field conditions, and plants would not emit CH4 at early growth and at a reduced rate near to ripening. M.S. Aulakh, J. Bodenbender, R. Wassmann, and H. Rennenberg A major portion (60-90 %) of the methane (CH4) emitted from rice fields to the atmosphere is transported through the aerenchyma of the rice plants. However, a rapid and accurate method to study the CH4 transport capacity (MTC) of rice plants is not available. We developed a gas sampling and analytical device based on a closed two-compartment chamber technique and analyzed the enrichment of the CH4 mixing ratio inside the shoot compartment of cylindrical cuvettes enclosing individual rice plants under ambient conditions. The computer-controlled analytical system consists of a gas chromatograph (GC), and a pressure-controlled autosampler for eight cuvettes (seven for plants and one for CH4-calibration gas). The system automates closure and opening of plant cuvettes using pneumatic pressure, air sample collection and injection into the GC, and CH4 analysis. It minimizes sources of error during air sampling by continuously mixing headspace air of each cuvette, maintaining pressure and composition of the headspace inside the cuvettes, purging the dead volumes between the sampler induction tube and GC, and running a reference CH4-calibration gas sample in each cycle. Tests showed that the automated system is a useful tool for accurate sampling of headspace air of cylindrical cuvettes enclosing individual rice plants and enables the rapid and accurate fully automated analysis of CH4 in the headspace air samples. A linear relationship was obtained between CH4 transported by rice plants of two cultivars (IR72, a high-yielding dwarf, and Dular, a traditional tall cultivar) and concentration of CH4 up to 7,500 ppm used for purging the nutrient culture solution surrounding the roots in the root compartment of the chamber. Further increase in CH4 emission by shoots was not observed at 10,000 ppm CH4 concentration in the root compartment of the chamber. The MTC of rice IR72 was measured at six development stages; it was lowest at the seedling stage, increasing gradually until panicle initiation. There was no further change at flowering, but a marked decrease at maturity was noted. These results suggest that the plants have 45-246% greater potential to transport CH4 than the highest CH4 emission rates reported under field conditions, and plants would not emit CH4 at early growth and at a reduced rate near to ripening. H. Denier van der Gon, P. van Bodegom, S. Houweling, P. Verburg, and N. van Breemen The uncertainty in the CH4 source strength of rice paddies is among the highest of all sources in the global CH4 budget. Methods to estimate the source strength of rice paddies can be divided in two categories; bottom-up scaling methodologies (upscaling) and top-down scaling methodologies (downscaling). A brief review of upscaling and downscaling methodologies is presented. The combination of upscaling and downscaling methodologies is proposed as a potential method to reduce the uncertainty in the regional CH4 source strength of rice paddies. Some preliminary results based on upscaling and downscaling are presented and the limitations of the approaches are discussed. The first case study focuses on upscaling by using a field-scale model in combination with spatial databases to calculate CH4 emissions for the Island of Java. The reliability of upscaling results are limited by the uncertainty in model input parameters like soil properties and organic carbon management. Because controlling variables like harvested rice area may change on relatively short time scales, a land use change model (CLUE) was used to quantify the potential land use changes on Java in the period 1994-2010. The predicted changes were evaluated using the CH4 emission model. Temporal scaling by coupling land use change models and emission models is necessary to answer policy related questions on future greenhouse gas emissions. In a downscaling case study, we investigate if inverse modelling can constrain the emissions from rice fields by testing a standard and a low CH4 from rice fields scenario (80 and 30 Tg CH4.yr-1, respectively). The results of this study are not yet conclusive, to obtain fine-resolution CH4 emission estimates over the Southeast Asian continent the monitoring network atmospheric mixing ratios needs to be extended and located closer to the continental sources. R.L. Sass, F.M. Fisher, Jr., and Y. Huang In this paper, we review the process-level studies that the authors have performed in rice fields of Texas since 1989 and the development of a semi-empirical model based on these studies. In this model, it is hypothesized that methanogenic substrates are primarily derived from rice plants and added organic matter. Rates of methane (CH4) production in flooded rice soils are determined by the availability of methanogenic substrates and the influence of climate, soil, and agronomic factors. Rice plant growth and added carbon control the fraction of CH4 emitted. The amount of CH4 transported from the soil to the atmosphere is determined by the rates of production and the emitted fraction. Model calibration against observations from single rice-growing season in Texas, USA, without organic amendments and with continuous irrigation demonstrated that the seasonal variation of CH4 emission is regulated by rice biomass and cultivar type. A further validation of the model against measurements from irrigated rice paddy soils in various regions of the world, including Italy, China, Indonesia, Philippines, and the United States, suggests that CH4 emission can be predicted from rice net productivity, cultivar character, soil texture, temperature, and organic matter amendments. Modeling trace gas emissions from agricultural ecosystems C. Li A computer simulation model was developed for predicting trace gas emissions from agricultural ecosystems. The denitrification-decomposition (DNDC) model consists of two components. The first component, consisting of the soil climate, crop growth, and decomposition submodels, predicts soil temperature, moisture, pH, Eh, and substrate concentration profiles based on ecological drivers (e.g., climate, soil, vegetation, and anthropogenic activity). The second component, consisting of the nitrification, denitrification, and fermentation submodels, predicts NH3, NO, N2O, and CH4 fluxes based on the soil environmental variables. Classical laws of physics, chemistry or biology, or empirical equations generated from laboratory observations were used in the model to parameterize each specific reaction. The entire model links trace gas emissions to basic ecological drivers. Through validation against data sets of NO, N2O, CH4, and NH3 emissions measured at four agricultural sites, the model showed its ability to capture patterns and magnitudes of trace gas emissions. Methane production, oxidation, and emission from Indian rice soils N. Sethunathan, S. Kumaraswamy, A. Kumar Rath, B. Ramakrishnan, T.K. Adhya, and V.R. Rao Experiments were conducted to investigate methane (CH4) production, oxidation, and emission from flooded rice soils. Incorporation of green manure (Sesbania rostrata) into rice fields led to a several-fold increase of CH4 emission. Stimulatory effect of organic sources on CH4 production in soil samples was noticed even under nonflooded conditions. Addition of rice straw at 1% w/w to nonflooded soil samples held at -1.5 MPa effected a 230-fold increase in CH4 production over that in corresponding unamended soil samples at 35 d, as compared with a 3-fold increase in rice straw-amended soil over that in unamended soil under flooded conditions. In a study involving two experimental field sites differing in water regimes but planted to the same rice cultivar (cv Gayatri) and fertilized with prilled urea at 60 kg N ha-1, the field plots with deep submergence of around 30 cm (site I) emitted distinctly more CH4 than did the plots with continuous water depth of 3-6 cm (site II). Likewise, in another incubation study, CH4 production in flooded soil samples increased with progressive increase in standing water column from 5 mm to 20 mm. Application of carbamate insecticide at 2 kg ai ha-1 to rice fields retarded CH4 emission through enhanced CH4 oxidation. Hexachlorocyclohexane was found to be inhibitory to CH4 emission. The results suggest the need for extensive research efforts to develop technologies with dual objectives of environmental protection and crop productivity. Mechanisms of crop Management impact on methane emissions from rice fields in Los Baños, Philippines R. Wassmann, L.V. Buendia, R.S. Lantin, C.S. Bueno, L.A. Lubigan, A. Umali, N.N. Nocon, A.M. Javellana, and H.-U. Neue This article comprise 4 years of field experiments on methane emissions from rice fields conducted at Los Baños, Philippines. The experimental lay-out allowed automated measurements of methane emissions as effected by water regime, soil amendments (mineral and organic) and cultivars. In addition to emission records over 24 hours, ebullition and dissolved methane in soil solution were recorded in weekly intervals. Emission rates varied in a very wide range from 5 to 634 kg CH4 ha-1 depending on season and crop management. In 1994 and 1996 experiments, field drying at mid-tillering reduced methane emissions by 15% to 80% as compared to continuous flooding, without a significant effect on grain yield. The net-impact of mid-tillering drainage was diminished when (i) rainfall was strong during the drainage period and (ii) emissions in the continuously flooded field were suppressed by very low low levels of organic substrate. Five cultivars were tested in dry and wet season 1995. The cultivar IR72 gave higher methane emissions than the other cultivars including the new plant type (IR65597) with an enhanced yield potential. Incorporation of rice straw into the soil resulted in an early peak of methane emission rates. About 66% of the total seasonal emission from rice straw-treated plots was emitted during vegetative stage. Methane fluxes generated from the application of straw were 34 times higher than with the use of urea. Application of green manure (Sesbania rostrata) gave only threefold increase in emission as compared to urea treated plots. Application of ammonium sulfate significantly reduced seasonal emission as compared to urea application. Correlation between emissions and combined dissolved methane concentrations (from 0 to 20 cm) gave a significant R2 of 0.95 (urea + rice straw), and 0.93 (urea + Sesbania) whereas the correlation with dissolved methane in the inorganically fertilized soils was inconsistent. A highly significant correlation (R2 =0.93) existed between emission and ebullition from plots treated with rice straw. These findings may stimulate further development of diagnostic tools for easy and reliable determination of methane emission potentials under different crop management practices. Methane emissions and mitigation options in irrigated rice fields in southeast China W.F. Lu, W. Chen, B.W. Duan, W.M. Guo, Y. Lu, R. Lantin, R. Wassmann, and H.-U. Neue Methane (CH4) emissions from rice fields were monitored in Hangzhou, China, from 1995 to 1998 by an automatic measurement system based on the "closed chamber technique." The impacts of water management, organic inputs, & cultivars on CH4 emission were evaluated. Under the local crop management system, seasonal emissions were observed ranging from 53 to 557 kg CH4 ha-1, with an average value of 182 kg CH4 ha-1. Methane emission patterns differed among rice seasons & were generally governed by temperature changes. Emissions showed an increasing trend in early rice & a decreasing trend in late rice. In a single rice field, CH4 emissions increased during the first half of the growing period & decreased during the second half. Drainage was a major modifier of seasonal CH4 emission pattern. The local practice of midseason drainage reduced CH4 emissions by 44 % as compared with continuous flooding; CH4 emissions could further be reduced by intermittent irrigation, yielding a 30% reduction as compared with midseason drainage. The incorporation of organic amendments promoted CH4 emission, but the amount of emission varied with the type of organic material & application method. Methane emission from fields where biogas residue was applied was 10-16 % lower than that from those given the same quantity (based on N content) of pig manure. Rice straw applied before the winter fallow period reduced CH4 emission by 11% as compared with that obtained from fields to which the same amount of rice straw was applied during field preparation. Broadcasting of straw instead of incorporation into the soil showed less emission (by 12 %). Cultivar selection influenced CH4 emission, but the differences were smaller than those among organic treatments & water regimes. Modifications in water regime & organic inputs were identified as promising mitigation options in southeast China. Methane emission from deepwater rice fields in Thailand N. Chareonsilp, C. Buddhaboon, P. Promnart, R. Wassmann, and R.S. Lantin Field experiments were conducted in the Prachinburi Rice Research Center (Thailand) from 1994 to 1998. The major objective was to study methane (CH4) emission from deepwater rice as affected by different crop management. Irrigated rice was investigated in adjacent plots, mainly for comparative purpose. The 4-year average in CH4 emission from deepwater rice with straw ash (burned straw) treatment was 46 mg m-2d-1 and total emission was 98 kg ha-1y-1. For irrigated rice the average emission rate and total emission for the straw ash treatment was 79 mg m-2d-1 and 74 kg ha-1y-1, respectively. Low emission rates may partially be related to acid sulfate soil of experimental site. Without organic amendment the seasonal pattern of methane emission from deepwater rice was correlated with an increase in biomass of rice plants. Emission rates from deepwater rice depend on the production of biomass and the straw management as well. Methane emission was greatest with straw incorporation followed by straw compost incorporation, zero-tillage with straw mulching and least with straw ash incorporation. The seasonal pattern of CH4 ebullition in deepwater rice was consistent with the seasonal emission, and the total ebullition corresponded to 50% to the total emission. Dissolved CH4 concentrations in the surface soil (0-5 cm) were similar to those in subsoil (5-15 cm), and the seasonal fluctuation of dissolved CH4 was also consistent with the seasonal CH4 emission. Increase in plant density and biomass of irrigated rice grown by pre-germinated seed broadcasting enhanced CH4 emission as compared to transplanting. Methane emission from rice fields at Cuttack, India T.K. Adhya, K. Bharati, S.R. Mohanty, B. Ramakrishnan, V.R. Rao, and N. Sethunathan Methane (CH4) emission from rice fields at Cuttack (State of Orissa, Eastrn India) has been recorded using an automatic measurement system (closed chamber method) from 1995-1998. Experiments were laid out to test the impact of water regime, organic amendment, inorganic amendment and rice cultivars. Organic amendments in conjunction with chemical-N (urea) effected higher CH4 flux over that of chemical-N alone. Application of Sesbania, Azolla and compost resulted in 132, 65 and 68 kg CH4 ha-1 in the wet season of 1996 when pure urea application resulted in 42 kg CH4 ha-1. Intermittent irrigation reduced emissions by 15% as compared to continuous flooding in the dry season of 1996. In the wet season of 1995, four cultivars were tested under rainfed conditions resulting in a range of emissions from 20 to 44 kg CH4 ha-1. Application of nitrification inhibitor dicyandiamide (DCD) inhibited while Nimin stimulated CH4 flux from flooded rice compared to that of urea-N alone.Wide variation in CH4 production and oxidation potentials was observed in rice soils tested. CH4 oxidation decreased with soil depth, fertilizer-N and nitrification inhibitors while organic amendment stimulated it. The results indicate that CH4 emission from the representative rainfed ecosystem at the experimental site averaged to 32 kg CH4 ha-1 yr-1. Methane emissions from irrigated rice fields in northern India (New Delhi) M.C. Jain, S. Kumar, R. Wassmann, S. Mitra, S.D. Singh, J.P. Singh, R. Singh, A.K. Yadav, and S. Gupta Methane emission fluxes from rice fields as affected by water regime, organic amendment and rice cultivar were measured at the Indian Agricultural Research Institute, New Delhi, using manual and automatic sampling technique of the closed chamber method. Measurements were conducted during 4 consecutive cropping seasons (July to October) from 1994 to 1997. Emission rates were in a very low range between 16 and 40 kg CH4 m -2 per season when the field was flooded permanently. These low emissions were indirectly caused by high percolation rates of the soil; frequent water replenishment resulted in constant inflow of oxygen in the soil. The local practice of intermittent flooding that encompasses short periods without standing water in the field further reduced emission rates. Over the course of 4 seasons, the total methane emission from intermittently irrigated fields was found to be 22% lower as compared to continuous flooding. The methane flux was invariably affected by the rice cultivar. The experiments conducted during 1995 with one cultivar developed by IRRI (IR72) and two local cultivars (Pusa 169 and Pusa Basmati) showed that the average methane flux from the intermittently irrigated plots without any organic amendment ranged between 10.2 and 14.2 mg m-2d-1. The impact of organic manure was tested in 1996 and 1997 with the varieties IR72 and Pusa 169. Application of organic manure (FYM+ wheat straw) in combination with urea (1:1 Nitrogen basis) enhanced methane emission by 12-20 % as compared to the fields treated with urea only. The site in New Delhi represents one example for very low methane emissions from rice fields. Emissions from other sites in Northern India may be higher than the observed values for New Delhi, but still in a low range in comparison to other rice growing regions in India. The abundant practice of intermittent irrigation - in combination with low organic inputs - is commonly found in Northern India and will virtually impede a further mitigation of methane emissions in significant quantities. In turn, the results of this study may provide clues to reduce emissions in other parts of India with higher baseline emissions. P. Setyanto, A.K. Makarim, A.M. Fagi, R. Wassmann, and L.V. Buendia Methane (CH4) emissions were determined from 1993 to 1998 using an automated closed chamber technique in irrigated and rainfed rice. In Jakenan (Central Java), the two consecutive crops encompass a gradient from low to heavy rainfall ('wet season crop') and from heavy to low rainfall ('dry season crop'), respectively. Rainfed rice was characterized by very low emission at the onset of the wet season and the end of the dry season. Persistent flooding in the irrigated fields resulted in relatively high emission rates throughout the two seasons. Seasonal averages in rainfed rice varied between 19 to 123 mg CH4 m-2 d-1 whereas seasonal averages in irrigated rice ranged from 71 to 217 mg CH4 m-2 d-1. The impact of organic manure was relatively small in the rainfed rice. In the wet season, farmyard manure was completely decomposed before CH4 emission initiated; rice straw resulted in 40 % increase in emission rates during this cropping season. In the dry season, intensive flooding in the early stage promoted high emissions from organically fertilized plots; seasonal emissions of farmyard manure and rice straw increased by 72 % and 37 %, respectively, as compared to mineral fertilizer. Four different rice cultivars were tested in irrigated rice. Average emission rates differed from season to season, but the total emissions showed a consistent ranking in wet and dry season depending on season length. The early-maturing Dodokan had lowest (101 and 52 kg CH4 ha-1) and the late-maturing Cisadane had highest emissions (142 and 116 kg CH4 ha-1). The high-yielding varieties IR64 and Memberamo had moderately high emission rates. These findings provide important clues for developing specific mitigation strategies for irrigated and rainfed rice. A four-year record of methane emissions from irrigated rice fields in the Beijing region of China Wang Zengyuan, Xu Yuchang, Li Zhen, Guo Yixian, R Wassmann, H.U Neue, R.S Lantin, L.V. Buendia, Ding Yuping, and Wang Zhanzhen Methane (CH4) emissions from irrigated rice fields were measured using an automatic sampling-measuring system with a closed chamber method in 1995-1998. Seasonal averages rates ranged from 11 to 364 mg m-2 day-1 depending on season, water regime and fertilizer application. Crop management typical for this region, i.e. midseason drainage and organic/mineral fertilizer application, resulted in emission of 279 and 139 mg CH4 m-2 day-1 in 1995 and 1997, respectively. This roughly corresponds to emissions observed in other rice growing areas of China. Emissions were very intense during the tillering stage, which accounted for 85 % of total annual emission, but were suppressed by low temperature in the late stage of the season. The local irrigation practice of drying at mid-season reduced emission rates by 23 %, as compared to continuous flooding. Further reduction of CH4 emissions could be attained by: (1) alternate flooding/drying, (2) shifting the drainage period to an earlier stage, or (3) splitting drainage into two phases of which one is in an earlier stage. Emission rates were extremely sensitive to organic amendments: seasonal emissions from fields treated with pig manure 15 to 35 times higher than those treated with ammonium sulfate in the corresponding season. On the basis of identical carbon inputs, methane emission potential varied among organic amendments. Rice straw had higher emissions than cattle manure but lower emissions than pig manure. Use of cultivar Zhongzhuo (modern japonica) reduced methane emission by 56 % and 50 %, in 1995 and 1997 respectively, as compared to Jingyou (japonica hybrid) and Zhonghua (tall japonica). The results give evidence that methane emissions from rice fields in Northern China can be reduced by a package of crop management options without affecting yields. R. Wassmann, N. Heinz-Ulrich, R.S. Lantin, L.V. Buendia, and H. Rennenberg The Interregional Research Program on Methane Emissions from Rice Fields established a network of eight measuring stations in five Asian countries. These stations covered different environments and encompassed varying practices in crop management. All stations were equipped with a closed chamber system designed for frequent sampling and long-term measurements of emission rates. Even under identical treatment, e.g. continuous flooding and no organic fertilizers, average emission rates varied from 15 to 200 kg CH4 per ha and season. Low temperatures limited CH4 emissions in temperate and subtropical stations such as Northern China and Northern India. Differences observed under given climates, e.g. within the tropics, indicated the importance of soil properties in regulating the CH4 emission potential. However, local variations in crop management superseded the impact of soil and climate related factors. This resulted in uniformly high emission rates of about 300 kg CH4 ha-1 season-1 for the irrigated rice stations in the Philippines (Maligaya) and China (Beijing and Hangzhou). The station in Northern India (Delhi) was characterized by exceptionally low emission rates of less than 20 kg CH4 ha-1 season -1 under local practice. These findings also suggest opportunities for reducing CH4 emission through a deliberate modification of cultural practice for most irrigated rice fields. R. Wassmann, N. Heinz-Ulrich, R.S. Lantin, K Makarim, C. Niwat, L.V. Buendia, and H. Rennenberg Methane emission rates were recorded automatically using the closed chamber technique in major rice-growing areas of Southeast Asia. The three experimental sites covered different ecosystems of wetland rice---irrigated, rainfed, and deepwater rice---using only mineral fertilizers. In Jakenan (Indonesia), the local water regime in rainfed rice encompassed a gradual increase (wet season) and a gradual decrease (dry season) in floodwater levels. Emission rates accumulated to 52 and 91 kg CH4 ha-1 season-1 corresponding to app. 40% of emissions from irrigated rice in each season. Distinct drainage periods within the season can drastically reduce CH4 emissions to less than 30 kg CH4 ha-1 season-1 as shown in Los Baños (Philippines). The reduction effect of this water regime as compared to irrigated rice varied from 20 % to 80 % from season to season. Methane fluxes from deepwater rice in Prachinburi (Thailand) were lower than from irrigated rice but accumulated to equally high seasonal values, i.e. ca. 99 kg CH4 ha-1 season-1, due to longer seasons and assured periods of flooding. Rice ecosystems with continuous flooding were characterized by anaerobic conditions in the soil. These conditions commonly found in irrigated and deepwater rice favored CH4 emissions. Temporary aeration of flooded rice soils, which is generic in rainfed rice, reduced emission rates due to low CH4 production and high CH4 oxidation. Based on these findings and the global distribution of rice area, irrigated rice accounts globally for 70-80 % of CH4 from the global rice area. Rainfed rice (ca. 15 %) and deepwater rice (ca. 10%) have much lower shares. In turn, irrigated rice represents the most promising target for mitigation strategies. Proper water management could reduce CH4 emission without affecting yields. Characterization of methane emissions in Asia: mitigation options and future research needs R. Wassmann, R.S. Lantin, H.U. Neue, L.V. Buendia, T.M. Corton, and Y. Lu Methane (CH4) emissions from rice fields were determined using automated measurement systems in China, India, Indonesia, Thailand and the Philippines. Mitigation options were assessed separately for different baseline practices of irrigated rice, rainfed, and deepwater rice. Irrigated rice is the largest source of CH4 and also offers more options to modify the crop management for reducing these emissions. Depending on the baseline practices, optimizing irrigation patterns by additional drainage periods in the field or an early timing of mid-season drainage accounted for 7 - 80% of CH4 emissions. In baseline practices with high organic amendments, use of compost (58-63 %), biogas residues (10-16%), and direct wet seeding (16-22%) should be considered as mitigation options. In baseline practices using prilled urea as sole N source, use of ammonium sulfate could reduce CH4 emission by 10-67%. In all rice ecosystems, CH4 emissions can be reduced by fallow incorporation (11 %) and mulching (11 %) of rice straw as well as addition of phosphogypsum (9-73%). However, in rainfed and deepwater rice, mitigation options are very limited both in number and potential gains The assessment of these crop management options includes their total factor productivity and possible adverse effects. Due to higher nitrous oxide (N2O) emissions, changes in water regime are only recommended for rice systems with high baseline emissions of CH4. Key objectives of future research are identifying and characterizing high-emitting rice systems, developing site-specific technology packages, ascertaining synergies with productivity, and accounting for N2O emissions. R. Matthews, R. Wassmann, and J. Arah The development of the MERES (Methane Emissions in Rice EcoSystems) model for simulating methane (CH4) emissions from rice-fields is described. The CERES-Rice crop simulation model was used as a basis, employing the existing routines simulating soil organic matter (SOM) decomposition to predict the amount of substrate available for methanogenesis. This was linked to an existing sub-model, described elsewhere in this volume, which calculates steady-state fluxes and concentrations of CH4 and O2 in flooded soils. Extra routines were also incorporated to simulate the influence of the combined pool of alternative electron acceptors in the soil (i.e. NO3-, Mn4+, Fe3+, SO42-) on CH4 production. The rate of substrate supply is calculated in the SOM routines of the CERES-Rice model from (a) the rate of decomposition of soil organic material including that left from the previous crop and any additions of organic matter, (b) root exudates (modified from the original CERES-Rice model using recent laboratory data), and (c) the decomposition of dead roots from the current crop. A fraction of this rate of substrate supply, determined by the concentration of the oxidised form of the alternative electron acceptor pool, is converted to CO2 by bacteria which out-compete the methanogenic bacteria, thereby suppressing CH4 production. Any remaining fraction of the substrate supply rate is assumed to be potentially available for methanogenesis. The CH4 dynamics sub-model uses this potential methanogenesis rate, along with a description of the root length distribution in the soil profile supplied by the crop model, to calculate the steady-state concentrations and fluxes of O2 and CH4. The reduced form of the alternative electron acceptor pool is allowed to re-oxidise when soil pores fill with air if the field is drained. The MERES model was able to explain well the seasonal patterns of CH4 emissions in an experiment involving mid- and end-season drainage and additions of organic material at IRRI in the Philippines. R.B. Matthews, and R. Wassmann As part of a series of papers describing the use of a simulation model to extrapolate experimental measurements of methane (CH4) emissions from rice paddies in Asia, and to evaluate the large-scale effect of various mitigation strategies, the collation and derivation of the spatial databases used is described. Daily weather data, including solar radiation, minimum and maximum temperatures, and rainfall were collated from 46 weather stations from the five countries in the study, namely; China, India, Indonesia, Philippines and Thailand. Quantitative soils data relevant to the input requirements of the model were derived by combining data from the World Inventory of Soil Emissions (WISE) database, the ISIS database, and the FAO Digital Soil Map of the World (FAO-DSMW). These data included soil pH, organic carbon content, sand, silt and clay fractions, and iron content, for top and subsoil layers, and average values of bulk density and available water capacity for the whole profile. Data on the areas allocated to irrigated, rainfed, upland and deepwater rice at province or district level were derived from the Huke & Huke (1997) database developed at IRRI. Using a geographical information system (GIS), a series of geo-referenced data-sets on climate, soils and land use were derived for each country, at province or district level. A summary of the soil related derived databases are presented and their application for use in global change modelling discussed. R. Matthews, R. Wassmann, L. Buendia, and J. Knox The MERES (Methane Emissions from Rice EcoSystems) simulation model was tested using experimental data from IRRI and Maligaya in the Philippines, and from Hangzhou in China. There was good agreement between simulated and observed values of total above-ground biomass, root weight, grain yield, and seasonal methane emissions. The importance of the contribution of the rice crop to CH4 emissions was highlighted. Rhizodeposition (root exudation and root death) was predicted to contribute about 380 kg C ha-1 of methanogenic substrate over the season, representing 37% of the total methanogenic substrate from all sources when no organic amendments were added. A further 225 kg C ha-1 (22%) was predicted to come from previous crop residues, giving a total of around 60% originating from the rice crop, with the remaining 41% coming from the humic fraction of the soil organic matter (SOM). Sensitivity analysis suggested that the parameter representing transmissivity to gaseous transfer per unit root length (r) was important in determining seasonal CH4 emissions. As this transmissivity increased, more O2 was able to diffuse to the rhizosphere, so that CH4 production by methanogens was reduced and more CH4 was oxidised by methanotrophs. These effects outweighed the opposing influence of increased rate of transport of CH4 through the plant, so that the overall effect was to reduce the amount of CH4 emitted over the season. Varying the root/shoot ratio of the crop was predicted to have little effect on seasonal emissions, the increased rates of rhizodeposition being counteracted by the increased rates of O2 diffusion to the rhizosphere. Increasing the length of a mid-season drainage period reduced CH4 emissions significantly, but periods longer than 6-7 days also decreased rice yields. Organic amendments with low C/N ratios were predicted to be more beneficial, both in terms of enhancing crop yields, and in reducing CH4 emissions, even when the same amount of C was applied. This was due to higher rates of immobilisation of C into microbial biomass, removing it temporarily as a methanogenic substrate. R. Matthews, R. Wassmann, J. Knox, and L. Buendia The process-based crop/soil model MERES (Methane Emissions from Rice EcoSystems) was used together with daily weather data, spatial soils data, and rice growing statistics to estimate the annual methane emissions from China, India, Indonesia, Philippines and Thailand under various crop management scenarios. Four crop management scenarios were considered: (a) a 'baseline' scenario assuming no addition of organic amendments or field drainage during the growing season, (b) addition of 3000 kg DM ha-1 of green manure at the start of the season but no field drainage, (c) no organic amendments, but drainage of the field for a 14-day period in the middle of the season and again at the end of the season, and (d) addition of 3000 kg DM ha-1 of green manure and field drainages in the middle and end of the season. For each scenario, simulations were made at each location for irrigated and rainfed rice ecosystems in the main rice growing season, and for irrigated rice in the second (or 'dry') season. Overall annual emissions (Tg CH4 y-1) for a province/district were calculated by multiplying the rates of CH4 emission (kg CH4 ha-1 y-1) by the area of rice grown in each ecosystem and in each season obtained from the Huke & Huke (1997) database of rice production. Using the baseline scenario, annual CH4 emissions for China, India, Indonesia, Philippines and Thailand were calculated to be 3.73, 2.14, 1.65, 0.14 and 0.18 Tg CH4 y-1, respectively. Addition of 3000 kg DM ha-1 green manure at the start of the season increased emissions by an average of 128% across the five countries, with a range of 74% to 259%. Drainage of the field in the middle and at the end of the season reduced emissions by an average of 13% across the five countries, with a range of ?10% to ?39%. The combination of organic amendments and field drainage resulted in an increase in emissions by an average of 86% across the five countries, with a range of 15% to 176%. The sum of CH4 emissions from these five countries, comprising about 70% of the global rice area, ranged from 6.49 to 17.42 Tg CH4 y-1 depending on the crop management scenario. Influence of six nitrification inhibitors on methane production in a flooded alluvial soil Kollah Bharati, Santosh R. Mohanty, P.V.L. Padmavathi, Vavilala R. Rao, and Tapan K. Adhya The influence of six nitrification inhibitors (NI) on CH4 production in an alluvial soil under flooded condition was studied in a laboratory incubation experiment. The inhibition of CH4 production followed the order of sodium azide > dicyandiamide (DCD) > pyridine > aminopurine > ammonium thiosulfate > thiourea. Inhibition of CH4 production in DCD amended soils was related to a high redox potential, low pH, low Fe2+ and lower readily mineralizable carbon content as well as lower population of methanogenic bacteria and their activity. In the presence of higher levels of urea-N (40 mg), the inhibitory effect of DCD was only partially alleviated. Results indicate that several NIs can differentially regulate CH4 production in a flooded alluvial soil. P.M. van Bodegom, P.A. Leffelaar, A.J.M. Stams, and R. Wassmann Estimates of global methane emissions, to which rice cropping systems contribute significantly, are uncertain. The variability and uncertainty of variables governing emission rates and the sensitivity of emissions to these variables determine the accuracy of methane emission estimates. A good tool for quantification of sensitivities is a process-based model. This paper describes a model that has been validated previously by experimental data. Variability and uncertainty in processes and variables underlying methane emissions are reviewed and the sensitivities of modelled methane emission estimates for process variables are tested. The sensitivity analysis is carried out for two sites in the Philippines at which methane emissions have been measured for several years. The sensitivities of the model are compared to measured sensitivities, both as a function of input parameters. The model sensitivity analysis shows that the system is not sensitive to mechanisms of methane production or the pathway of gas transport through the plant. Methane emissions are very sensitive, however, to the description of substrate supply (both from the soil and from organic fertilisers). Unfortunately, this description also represents a main uncertainty. Uncertainty in methane emission estimates will thus remain large as long as these processes are not well quantified. Influence of Azolla on CH4 emission from rice fields Z. Ying, P.l Boeckx, C. Guanxiong, and O. Van Cleemput Azolla is an aquatic fern that has been used successfully as dual cropping in wetland rice. Rice fields are a major source of atmospheric CH4, which is an important greenhouse gas. In this study, field and laboratory experiments gave evidence, which suggest that growing Azolla as dual cropping with wetland rice could enhance CH4 emission from rice fields. In pot experiments, indications were obtained that Azolla could mediate CH4 transport from the flood water of a paddy soil into the atmosphere. It was also found that, due to the presence of Azolla, chemical soil properties could be developed, stimulating CH4 production and decreasing in situ CH4 removal. Field experiments in China also suggest that Azolla could enhance CH4 emission from rice fields. B. Wang and K. Adachi Greenhouse experiments were conducted under subtropical conditions to understand the mechanism of rice cultivar differences in methane (CH4) emission. Three rice cultivars were studied. Differences in CH4 emission rates among the three rice cultivars became evident in the middle and late growth stages. Rice root exudates per plant measured as the total released C were significantly different among rice cultivars. The effect of root exudates on CH4 production in soil slurry differed accordingly. The amount of root exudates was not significantly different among rice cultivars when it was computed on a dry matter basis, indicating that it is positively correlated to root dry matter production. The root methane-oxidizing activity differed among rice cultivars. IR65598 had a higher oxidative activity than IR72 and Chiyonishiki. Root air space was not significantly different among rice cultivars at the late growth stage, indicating that it is probably not a factor contributing to cultivar difference in methane emission. The population level of methanogenic bacteria (MGB) differed significantly in soil grown to different rice cultivars, but not in roots, at booting stage, and ripening stage. Methanotrophic bacteria (MOB) population differed significantly in roots among rice cultivars at ripening. Rice cultivars with less ineffective tillers, small root system, high root oxidative activity, and high harvest index are ideal for mitigating CH4 emission in paddy fields. A. Hou, Z. Wang, G. Chen, and W.H. Patrick, Jr. An incubation experiment to determine the effects of organic and chemical N fertilizers on methane (CH4) production potential in a Chinese flooded rice soil was conducted. Organic matter, added as rice straw and organic manure, increased CH4 production rate significantly. Chemical N fertilizers such as, ammonium bicarbonate (AB), modified ammonium bicarbonate (MAB), and urea (U) did not show a clear effect when they were applied with rice straw. Field results may be very different because of the involvement of rice plants. Organic manure showed different promoting effects on CH4 production rate. Pig manure stimulated the production rate most, followed by chicken and cattle manure. This difference in organic manure was not related to either total C added to the system or to C/N. The study on bacteria groups related to CH4 production indicated that the different effects of organic matter may be closely related to content of easily decomposable organic matter. A significant linear relationship between CH4 production and the logarithm of the number of zymogenic bacteria was found with an r value of 0.96. This finding suggests that the number of zymogenic bacteria may be used as an index to predict CH4 production potential in flooded rice fields and other wetlands. Methane emissions from irrigated rice fields in northern India (New Delhi) M.C. Jain, S. Kumar, R. Wassmann, S. Mitra, S.D. Singh, J.P. Singh, Ramlakhan Singh, A.K. Yadav, and S. Gupta Methane emission from rice fields as affected by water regime, organic amendment and rice cultivar were measured at the Indian Agricultural Research Institute, New Delhi, using manual and automatic sampling technique of the closed chamber method. Measurements were conducted during 4 consecutive cropping seasons (July to October) from 1994 to 1997. Emission rates were low, 16 and 40 kg CH4 m -2 per season when the field was flooded permanently. These low emissions were indirectly caused by high water percolation rates where frequent water replenishment resulted in constant inflow of oxygen in the soil. The local practice of intermittent flooding that encompasses short periods without standing water in the field further reduced emission rates. Over the course of 4 seasons, the total methane emission from intermittently irrigated fields was 22% lower as compared to continuous flooding. The experiments conducted during 1995 with one cultivar developed by IRRI (IR72) and two local cultivars (Pusa 169 and Pusa Basmati) showed that the average methane flux from the intermittently irrigated plots without any organic amendment ranged between 10.2 and 14.2 mg m-2d-1. The impact of organic manure was tested in 1996 and 1997 with the varieties IR72 and Pusa 169. Application of organic manure (FYM+ wheat straw) in combination with urea (1:1 Nitrogen basis) enhanced methane emission by 12-20 % as compared to the fields treated with urea only. The rice cultivars did not show marked difference in methane emission from rice paddy fields. The site in New Delhi represents one example for very low methane emissions from rice fields. Emissions from other sites in Northern India may be higher than the observed values for New Delhi, but still in a low range in comparison to other rice growing regions in India. The abundant practice of intermittent irrigation - in combination with low organic inputs - is commonly found in Northern India and will impede further significant mitigation of methane emissions. In turn, the results of this study may provide clues to reducing emissions in other parts of India that have higher baseline emissions. The effects of cultural practices on methane emission from rice fields J.-Y. Ko and H.-W. Kang A field experiment was conducted in a clayey soil to determine the effects of cultural practices on methane emissions from rice fields. The factors evaluated were a) direct seeding on dry vs wet soil, b) age of transplanted seedlings (8-d-old and 30-d-old), and c) fall vs spring plowing. Methane emissions were measured weekly throughout the rice-growing season using a closed static chamber technique. Transplanted 8-d-old seedlings showed the highest emission of 42.4 g CH4 m-2 season-1, followed by transplanted 30-d-seedlings (40.3 g CH4 m-2 season-1 ), and direct seeding on wet soil (37.1 g CH4 m-2 season-1 ). Direct seeding on dry soil registered the least emission of 26.9 g CH4 m-2 season-1.Thus transplanting 30-d-old seedlings, direct seeding on wet soil, and direct seeding on dry soil reduced CH4 emission by 5%, 13%, and 37%, respectively, when compared with transplanting 8-d-old seedlings. Methane emission under spring plowing was 42.0 g CH4 m-2 season-1 and under fall plowing was 31.3 g CH4 m-2 season-1. The 26% lower emission in the field plowed in spring was caused by degradation of organic matter over the winter. Methane emission from irrigated and intensively managed rice fields in Central Luzon (Philippines) T.M. Metra-Corton, J.B. Bajita, F.S. Grospe, R.R. Pamplona, C.A. Asis, Jr., R. Wassmann, and R.S. Lantin Methane (CH4) emissions were measured with an automated system in Central Luzon, the major rice producing area of the Philippines. Emission records covered 9 consecutive seasons from 1994 to 1998 and showed a distinct seasonal pattern: an early flush of CH4 before transplanting, an increasing trend in emission rates reaching maximum towards grain ripening, and a second flush after water is withdrawn prior to harvesting. Local practice of crop management, which consists of continuous flooding and urea application, resulted in 79-184 mg CH4 m-2 d-1 in the dry season (DS) and 269-503 mg CH4 m-2 d-1 in the wet season (WS). Higher emissions in the WS may be attributed to more labile carbon accumulation during the dry fallow period before the WS cropping as shown by higher %OC. Incorporation of sulfate into the soil reduced CH4 emission rates. The use of ammonium sulfate as nitrogen fertilizer in place of urea resulted in a 25-36% reduction in CH4 emissions. Phosphogypsum reduced CH4 emissions by 72% when applied in combination with urea fertilizer. Mid-season drainage reduced CH4 emission by 43%, which can be explained by the influx of oxygen into the soil. The practice of direct seeding instead of transplanting resulted in a 16-54% reduction in CH4 emission, but the mechanisms for the reductive effect are not clear. Addition of composted rice straw increased CH4 emission by only 23-30% as compared with the 162-250% increase in emissions with the use of fresh rice straw. Chicken manure combined with urea did not increase CH4 emission. Fresh rice straw has wider C/N ratio (25 to 45) while rice straw compost has C/N = 6 to 10 and chicken manure has C/N = 5 to 8. Modifications in inorganic and organic fertilizer management and water regime do not adversely affect grain yield and are therefore potential mitigation options. Direct seeding has a lower yield potential than transplanting, but is getting increasingly popular in farmers' practice due to labor savings. Combined to a package of technologies, CH4 emission can best be reduced by: (1) the practice of mid-season drainage instead of continuous flooding, (2) the use of sulfate-containing fertilizers such as ammonium sulfate and phosphogypsum combined with urea; (3) direct seeding crop establishment; and (4) use of low C/N ratio organic fertilizer such as chicken manure and rice straw compost. Varietal difference of methane emission from Korean rice cultivars Y.-K. Shin and S.-H. Yun Methane emission from eight cultivars planted under uniform field conditions was measured by the closed static chamber method. Mean daily CH4 emission and seasonally integrated CH4 flux followed similar trends among the different varieties irrespective of growth duration. The CH4 flux (g CH4 m-2) among the varieties was in the order of Dasanbyeo (36.9) < Ilpumbyeo (42.9) < Gyehwabyeo (47.8) < Daeanbyeo (50.9) < Dongjinbyeo (58.8) < Hwaseongbyeo (59.7) < Odaebyeo (62.9) < Mangeumbyeo (76.0). No significant correlation was observed between CH4 emission factor and root distribution in the 0-5 cm soil profile and dry matter weight in the canopy at heading stage. Estimation of regional methane emission from rice fields using simple atmospheric diffusion models L. Jianguo, Z. Yuanhang, S. Kesheng, S. Min, Z. Limin, L. Sihua, S. Slanina, and H.A.C. Denier van der Gon Two atmospheric diffusion models, Box model and ATDL (Atmospheric Turbulent and Diffusion Laboratory) model, were used to calculate regional methane (CH4) emissions of rice fields in Beijing area. Compared with conventional closed chamber measurements, the box model overestimated CH4 emission because of meteorological conditions-the ground inverse layer was not favorable for the application of the model during the rice-growing season. The ATDL model, on the other hand, handled this unfavorable meteorological condition and gave reasonable CH4 emission estimates (about 6.1-8.5 mg m-2h-1) close to conventional measurements (about 0.3-14.3 mg m-2h-1) in June, a period generally characterized with significant CH4 emission from rice fields. In September, CH4 emission as measured with closed chambers was negligible (about 0-0.3 mg m-2h-1), but the ATDL model still calculated it to be (about 2.8-5.3 mg m-2h-1), albeit at a low level and considerably below the June emissions level. This discrepancy cannot be explained at present and needs further study. The presence of some local CH4 sources such as a soil CH4 reservoir emitting CH4 from ditches formed in autumn rice field is a most likely cause. The application of atmospheric diffusion models for regional CH4 emission estimation depends greatly on meteorological conditions. Moreover, the models tend to give much more reliable results during periods of rather high CH4 emission. This coincides with the time that such regional CH4 emission estimates are most valuable. The atmospheric diffusion models complement the closed chamber method by providing integrated CH4 emission estimates from 1-100 km2 rice areas. Detailed information about agricultural management of rice fields and other potential CH4 sources within the study region are necessary to better understand the integrated regional emission estimates. Simulation of CH4 production in anaerobic rice soils by a simple two-pool model Y. Lu, J.R.M. Arah, R. Wassmann, and H.-U. Neue Methane (CH4) is produced in flooded rice fields by anaerobic decomposition of applied organic residues, root-derived materials and native soil organic matter (SOM). Since CH4 is an important greenhouse gas it is important to understand, and to be able to model, the processes which produce it. Anoxic incubation of soils employed in the cultivation of irrigated rice, with and without the addition of various potentially-available organic substrates, provides information on potential CH4 emissions which can be incorporated into process-based models. In this study, a simple two-pool model is employed to simulate the CH4 production of a number of anaerobically-incubated rice soils, and their responses to amendment with a variety of organic substrates. The model differs from most accounts of SOM transformation in that kinetics are microbially-mediated rather than first-order. Simulation yields a reproduction of the general trends of CH4 production in response to amendments of acetate, glucose and rice straw. |
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Modeling rice-plant-mediated methane emission Modeling trace gas emissions from agricultural ecosystems Methane production, oxidation, and emission from Indian rice soils
Mechanisms of
crop Management impact on methane emissions from rice fields in Methane emissions and mitigation options in irrigated rice fields in southeast China Methane emission from deepwater rice fields in Thailand Methane emission from rice fields at Cuttack, India Methane rmissions from irrigated rice fields in northern India (New Delhi) A four-year record of methane emissions from irrigated rice fields in the Beijing region of China Characterization of methane emissions in Asia: mitigation options and future research needs Influence of six nitrification inhibitors on methane production in a flooded alluvial soil Influence of Azolla on CH4 emission from rice fields Methane emissions from irrigated rice fields in northern India (New Delhi) The effects of cultural practices on methane emission from rice fields Methane emission from irrigated and intensively managed rice fields in Central Luzon (Philippines) Varietal difference of methane emission from Korean rice cultivars Estimation of regional methane emission from rice fields using simple atmospheric diffusion models Simulation of CH4 production in anaerobic rice soils by a simple two-pool model |
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