Cumulative CH4 Emissions Research Articles

Greenhouse gas emissions in response to straw incorporation, water management and their interaction in a paddy field in subtropical central China

ABSTRACTA field experiment was conducted to study the effects of combination of straw incorporation and water management on fluxes of CH4, N2O and soil heterotrophic respiration (Rh) in a paddy field in subtropical central China by using a static opaque chamber/gas chromatography method. Four treatments were set up: two rice straw incorporation rates at 0 (S1) and 6 (S2) t ha−1 combined with two water managements of intermittent irrigation (W1, with mid-season drainage) and continuous flooding (W2, without mid-season drainage). The cumulative seasonal CH4 emissions for the treatments of S1W2, S2W1 and S2W2 increased significantly by 1.84, 5.47 and 6.63 times, respectively, while seasonal N2O emissions decreased by 0.67, 0.29 and 1.21 times, respectively, as compared to S1W1 treatment. The significant increase in the cumulative Rh for the treatments S1W1, S2W1 and S2W2 were 0.54, 1.35 and 0.52 times, respectively, in comparison with S1W2. On a seasonal basis, both the CO2-equivalents (CO2e) and yield-scaled CO2e (GHGI) of CH4 and N2O emissions increased with straw incorporation and continuous flooding, following the order: S2W2>S2W1>S1W2>S1W1. Thus, the practices of in season straw incorporation should be discouraged, while mid-season drainage is recommended in paddy rice production from a point view of reducing greenhouse gas emissions.

Greenhouse gas emission from direct seeded paddy fields under different soil water potentials in Eastern India

In the anticipated water scarcity and global warming scenario; it is imperative to identify suitable irrigation scheduling strategy in paddy fields for increasing water productivity and mitigating greenhouse gas (GHG) emissions. We conducted a two year (dry season of 2014 and 2015) field experiment for irrigation scheduling based on tensiometric measurement of soil water potential (SWP) in order to quantify temporal and seasonal variations in GHGs emissions and their trade off relationship at five levels of SWPs viz. SWP 1 (−20kPa), SWP 2 (−30kPa), SWP 3 (−40kPa), SWP 4 (−50kPa) and SWP 5 (−60kPa), in addition to the traditional practice of growing flooded rice (CF). Fluxes of methane (CH4) and nitrous oxide (N2O) during the growing period were measured using manual closed chamber-gas chromatograph and the carbon dioxide (CO2) flux was measured using an infrared CO2 analyzer. A significant decrease in seasonal cumulative CH4 emission (30–60.2%) was recorded at different SWPs as compared to CF. In contrast, emission of CO2 and N2O increased by 12.9–26.6% and 16.3–22.1% respectively at SWPs 1 and 2; conversely, a significant decrease in emissions of these gases were observed at higher SWPs (SWPs 3–5). Among different SWP treatments, irrigation scheduling at SWP 2 maintained yield at par with CF with water saving of 32.9–41.1% and reduced CH4 emission (43–44.1%). However, due to increase in CO2 and N2O emission at SWP 2, there was no significant reduction in global warming potential (GWP) as compared with CF. Among different rice growth stages GHGs emission were predominant during vegetative growth stage. Regression relationship of GHGs emission with key soil parameters was employed to predict seasonal emissions of GHGs from paddy field. The results of this study suggest that scheduling irrigation at SWP 2 can be an effective strategy in order to save water, maintain rice yield and mitigate CH4 emission from direct seeded paddy fields in eastern India, however further research is needed to identify suitable management strategy for reducing CO2 and N2O emissions at SWP 2 in order to reduce the GWP.

Effects of Land-Use Conversion from Double Rice Cropping to Vegetables on Methane and Nitrous Oxide Fluxes in Southern China.

Compared with CO2, methane (CH4) and nitrous oxide (N2O) are potent greenhouse gases in terms of their global warming potentials. Previous studies have indicated that land-use conversion has a significant impact on greenhouse gas emissions. However, little is known regarding the impact of converting rice (Oryza sativa L.) to vegetable fields, an increasing trend in land-use change in southern China, on CH4 and N2O fluxes. The effects of converting double rice cropping to vegetables on CH4 and N2O fluxes were examined using a static chamber method in southern China from July 2012 to July 2013. The results indicate that CH4 fluxes could reach 31.6 mg C m−2 h−1 under rice before land conversion. The cumulative CH4 emissions for fertilized and unfertilized rice were 348.9 and 321.0 kg C ha−1 yr−1, respectively. After the land conversion, the cumulative CH4 emissions were −0.4 and 1.4 kg C ha−1 yr−1 for the fertilized and unfertilized vegetable fields, respectively. Similarly, the cumulative N2O fluxes under rice were 1.27 and 0.56 kg N ha−1 yr−1 for the fertilized and unfertilized treatments before the land conversion and 19.2 and 8.5 kg N ha−1 yr−1, respectively, after the land conversion. By combining the global warming potentials (GWPs) of both gases, the overall land-use conversion effect was minor (P = 0.36) with fertilization, but the conversion reduced GWP by 63% when rice and vegetables were not fertilized. Increase in CH4 emissions increased GWP under rice compared with vegetables with non-fertilization, but increased N2O emissions compensated for similar GWPs with fertilization under rice and vegetables.

Carbon balance of rewetted and drained peat soils used for biomass production: a mesocosm study

AbstractRewetting of drained peatlands has been recommended to reduce CO2 emissions and to restore the carbon sink function of peatlands. Recently, the combination of rewetting and biomass production (paludiculture) has gained interest as a possible land use option in peatlands for obtaining such benefits of lower CO2 emissions without losing agricultural land. This study quantified the carbon balance (CO2, CH4 and harvested biomass C) of rewetted and drained peat soils under intensively managed reed canary grass (RCG) cultivation. Mesocosms were maintained at five different groundwater levels (GWLs), that is 0, 10, 20 cm below the soil surface, representing rewetted peat soils, and 30 and 40 cm below the soil surface, representing drained peat soils. Net ecosystem exchange (NEE) of CO2 and CH4 emissions was measured during the growing period of RCG (May to September) using transparent and opaque closed chamber methods. The average dry biomass yield was significantly lower from rewetted peat soils (12 Mg ha−1) than drained peat soils (15 Mg ha−1). Also, CO2 fluxes of gross primary production (GPP) and ecosystem respiration (ER) from rewetted peat soils were significantly lower than from drained peat soils, but net uptake of CO2 was higher from rewetted peat soils. Cumulative CH4 emissions were negligible (0.01 g CH4 m−2) from drained peat soils but were significantly higher (4.9 g CH4 m−2) from rewetted peat soils during measurement period (01 May–15 September 2013). The extrapolated annual C balance was 0.03 and 0.68 kg C m−2 from rewetted and drained peat soils, respectively, indicating that rewetting and paludiculture can reduce the loss of carbon from peatlands.

Methane dynamics in the subarctic tundra: combining stable isotope analyses, plot- and ecosystem-scale flux measurements

Abstract. Methane (CH4) fluxes were investigated in a subarctic Russian tundra site in a multi-approach study combining plot-scale data, ecosystem-scale eddy covariance (EC) measurements, and a fine-resolution land cover classification scheme for regional upscaling. The flux data as measured by the two independent techniques resulted in a seasonal (May–October 2008) cumulative CH4 emission of 2.4 (EC) and 3.7 g CH4 m−2 (manual chambers) for the source area representative of the footprint of the EC instruments. Upon upscaling for the entire study region of 98.6 km2, the chamber measured flux data yielded a regional flux estimate of 6.7 g CH4 m−2 yr−1. Our upscaling efforts accounted for the large spatial variability in the distribution of the various land cover types (LCTs) predominant at our study site. Wetlands with emissions ranging from 34 to 53 g CH4 m−2 yr−1 were the most dominant CH4-emitting surfaces. Emissions from thermokarst lakes were an order of magnitude lower, while the rest of the landscape (mineral tundra) was a weak sink for atmospheric methane. Vascular plant cover was a key factor in explaining the spatial variability of CH4 emissions among wetland types, as indicated by the positive correlation of emissions with the leaf area index (LAI). As elucidated through a stable isotope analysis, the dominant CH4 release pathway from wetlands to the atmosphere was plant-mediated diffusion through aerenchyma, a process that discriminates against 13C-CH4. The CH4 released to the atmosphere was lighter than that in the surface porewater, and δ13C in the emitted CH4 correlated negatively with the vascular plant cover (LAI). The mean value of δ13C obtained here for the emitted CH4, −68.2 ± 2.0 ‰, is within the range of values from other wetlands, thus reinforcing the use of inverse modelling tools to better constrain the CH4 budget. Based on the IPCC A1B emission scenario, a temperature increase of 6.1 °C relative to the present day has been predicted for the European Russian tundra by the end of the 21st Century. A regional warming of this magnitude will have profound effects on the permafrost distribution leading to considerable changes in the regional landscape with a potential for an increase in the areal extent of CH4-emitting wet surfaces.

Yield-scaled global warming potential of two irrigation management systems in a highly productive rice system

Water management impacts both methane (CH4) and nitrous oxide (N2O) emissions from rice paddy fields. Although controlled irrigation is one of the most important tools for reducing CH4emission in rice production systems it can also increase N2O emissions and reduce crop yields. Over three years, CH4 and N2O emissions were measured in a rice field in Uruguay under two different irrigation management systems, using static closed chambers: conventional water management (continuous flooding after 30 days of emergence, CF30); and an alternative system (controlled deficit irrigation allowing for wetting and drying, AWDI). AWDI showed mean cumulative CH4 emission values of 98.4 kg CH4 ha−1, 55 % lower compared to CF30, while no differences in nitrous oxide emissions were observed between treatments ( p > 0.05). No yield differences between irrigation systems were observed in two of the rice seasons ( p > 0.05) while AWDI promoted yield reduction in one of the seasons ( p< 0.05). When rice yield and greenhouse gases (GHG) emissions were considered together, the AWDI irrigation system allowed for lower yield-scaled total global warming potential (GWP). Higher irrigation water productivity was achieved under AWDI in two of the three rice seasons. These findings suggest that AWDI could be an option for reducing GHG emissions and increasing irrigation water productivity. However, AWDI may compromise grain yield in certain years, reflecting the importance of the need for fine tuning of this irrigation strategy and an assessment of the overall tradeoff between relationships in order to promote its adoption by farmers.

Dolomite application enhances CH4 uptake in an acidic soil

Methane (CH4) is a potent greenhouse gas and agricultural soils are the main source of atmospheric CH4. Information regarding CH4 emission from acidic soils is limited in the literature. A laboratory study was conducted to examine CH4 emissions following dolomite application in an acidic paddy soil. Dolomite was applied to the acidic soil (Ultisol) under two levels of moisture and nitrogen (N) fertilizer in a factorial design. Dolomite was applied at the rates of 0, 1, and 2gkg−1 soil (D0, D1, and D2 respectively) under two moisture levels of 55% and 90% water-filled pore space (WFPS). Each treatment of dolomite under two moisture levels was further treated with 0 and 200mgNkg−1 soil. Soil moisture of 90% WFPS produced (p≤0.001) CH4 emissions while uptake was observed in 55% WFPS. Nitrogen fertilizer application significantly increased CH4 emissions in 90% WFPS while inhibited uptake in 55% WFPS. Maximum cumulative CH4 emission (1784.88μgCH4-Ckg−1) was observed under 90% WFPS in N fertilizer application without dolomite application. Application of dolomite decreased cumulative CH4 emissions by 39% in 90% WFPS, and enhanced CH4 uptake up to 15 times in 55% WFPS with D2 treatment in fertilizer treated soil. Results indicated that dolomite application has the potential to enhance the uptake and to decrease the emissions of CH4 in acidic soils.

Modelling enteric methane abatement from earlier mating of dairy heifers in subtropical Australia by improving diet quality

Milking cows typically dominate dairy farm greenhouse gas (GHG) emissions, but replacement heifers also contribute to farm emissions and can increase the emission intensity of milk production. In northern Australia, heifers generally graze poorer-quality subtropical pastures and in the absence of energy-dense supplementary feed during periods of low pasture growth, liveweight (LW) gain can be restricted. This modelling study examined the time required and enteric methane (CH4) emissions produced in raising dairy heifers to a target LW for first mating by feeding a diet assuming either constant (static) or variable (dynamic) nutritive values. Using a static approach (Australian Feeding Standards methodology), and assuming a target mating LW of 360 kg, growing heifers reached their target LW at ~18 months of age while consuming C4 grasses with a constant metabolisable energy content of 9.5 MJ/kg dry matter (DM) or 11 months of age on a diet of 11.0 MJ/kg DM. Enteric CH4 emissions were 1.2 and 0.8 t of carbon dioxide equivalents/heifer over the 18- and 11-month periods, respectively. To explore the extent with which climatic conditions influence seasonal pasture availability and nutritive value with a dynamic approach, we used a whole-farm biophysical model (SGS pasture model) to simulate diets with mean metabolisable energy values of 9.5 and 10.9 MJ/ kg DM. On average (±s.d.), heifers required 22 ± 4 and 17 ± 1 months, respectively, to reach target LW, with cumulative enteric CH4 emissions of 1.22 ± 0.20 and 0.72 ± 0.04 t carbon dioxide equivalents, respectively. The dynamic approach resulted in slower LW gain due to the variable nutritive value of the diet throughout the year, resulting in seasonal periods of LW plateauing or decline. Maintaining heifers on high-quality diets in subtropical northern Australia should result in increased daily LW gain, lower enteric CH4 emissions to mating LW and earlier calving. Together, these factors reduce their lifetime emission intensity of milk production.

Controlled irrigation mitigates the annual integrative global warming potential of methane and nitrous oxide from the rice–winter wheat rotation systems in Southeast China

Irrigation mode is an important factor in regulating CH4 and N2O emissions from croplands. However, there are no studies on the effects of irrigation mode practiced during the rice season on the annual integrative global warming potential (GWP) of CH4 and N2O in the rice–winter wheat rotation systems. Thus, a field experiment was designed to study the effects of controlled irrigation (CI) during the rice season on the annual integrative GWP of CH4 and N2O emissions from the rice–winter wheat rotation systems, with traditional irrigation (TI) as the control. A notable trade-off relationship between CH4 and N2O emissions was observed in the rice–wheat rotation systems under both CI and TI of rice. CI during the rice season had obvious subsequent effects on CH4 and N2O emissions from the following winter wheat season. Over the whole annual cycle, CI significantly reduced the cumulative CH4 emission (13.27kgha−1) by 80.6% than that from the TI fields (p<0.001), but did not cause a significant difference on the cumulative N2O emission (p>0.05). The integrative GWP of CH4 and N2O on a 100-year horizon for the CI rotation systems was 2720.35kgCO2ha−1, which was 41.1% lower than that for the TI fields (p<0.05). Moreover, the difference of rice and wheat yields between the CI and TI fields was not significant (p>0.05). This is the first study to investigate the effects of CI during the rice season on the annual integrative GWP of CH4 and N2O in a rice–winter wheat rotation system. Our results suggest that CI can significantly mitigate the annual integrative greenhouse effect caused by CH4 and N2O from the rice–winter wheat rotation systems, while ensuring the crop yields.

Irrigation Management and Greenhouse Gas Emissions in Uruguayan Rice Production Systems

Environmental impact and sustainability of agricultural systems and management practices leading to climate change mitigation are one of the most relevant issues to agricultural production nowadays. Mitigation is the process of reducing emissions or enhancing sinks of greenhouse gases (GHG), to limit global warming potential and restrict future climate change. The most relevant GHG are Carbon dioxide (CO2), Methane (CH4) and Nitrous Oxide (N2O). The steady increase of its concentrations in the atmosphere over several decades has led to enhance global warming. CH4 and N2O are the most relevant GHG emitted mainly in the agricultural sector. It is well known that water management has great impact on GHG emissions from rice paddy fields. One of the most important tools for rice crop production and mitigation of CH4 emission is the controlled irrigation. However, it could result in a N2O emission increase and reduced rice yields. For these reasons, it is remarkably important to assess the tradeoff relationship between both GHG and the effect on rice productivity. A 3 year field experiment with two different irrigation systems was set at southeast of Uruguay. Conventional water management (continuous flooding after 30 days of emergence, CF30) and an alternative irrigation system (controlled deficit irrigation allowing wetting and drying, AWDI) were compared. The objective was to study the effect of water management on GHG emission, water productivity and rice yields in order to identify strategies for further progress in sustainable intensification of Uruguayan rice. Results showed that mean cumulative CH4 emission values for AWDI were 55% lower than CF30 systems; on the other hand, there were no significant differences in N2O emission among systems. Significant yield differences were not observed in two of the rice seasons, while AWDI recorded a significant yield reduction in one of them. Total irrigation water applied and irrigation water productivity did not showed differences in two of the rice seasons, while CF30 reported a higher amount of water applied and lower water productivity in one of the seasons. It can be concluded that AWDI could be an option to enhance water productivity and GHG emission mitigation. However, grain yield can be compromised in AWDI systems. The adoption of these technology is based on the indispensable assess of an overall tradeoff between the risk of possible yield losses, total water used and GHG emissions.

Manure, biogas digestate and crop residue management affects methane gas emissions from rice paddy fields on Vietnamese smallholder livestock farms

Greenhouse gas (CH4 and N2O) emissions from rice paddy fields amended by differently treated manure and crop residue inputs [fresh manure (FM), composted manure (CM), liquid biogas digestate from manure (D), D mixed with biochar (D + B) or D mixed with rice straw and composted before application (CD + RS)], were compared in a field experiment, also including two mineral nitrogen fertiliser controls (N1, N2). The trial was performed on a degraded soil in Bac Giang Province in northern Vietnam with a three-crop per year rotation (summer rice–maize–spring rice). CH4 and N2O fluxes from the two rice crops were measured using static chambers. Fluxes of N2O were below or close to the detection limit at nearly all sampling times in both seasons and therefore considered negligible. However, the CH4 emissions were significant and their temporal pattern differed markedly between the rice seasons. In the summer rice season, the D + B + N1 and D + N1 treatments had significantly lower cumulative CH4 emissions (156 and 162 kg CH4 ha−1 crop−1) than CM + N1, CD + RS + N1 and FM + N1 treatments (217, 283 and 288 kg CH4 ha−1 crop−1, respectively). In the spring rice season, CH4 emissions were generally much lower, and the D + B + N1 and D + N1 treatments emitted significantly less CH4 (44 and 72 kg CH4 ha−1 crop−1) in comparison with treatments amended with FM + N1, CD + RS + N1 and CM + N1 (89, 124 and 137 kg CH4 ha−1 crop−1, respectively). Treatments amended with D + B + N1 or D + N1 therefore had the lowest emissions of methane per unit of rice grain yield.

Greenhouse gas emissions, soil quality, and crop productivity from a mono-rice cultivation system as influenced by fallow season straw management.

Straw management during fallow season may influence crop productivity, soil quality, and greenhouse gas (GHG) emissions from rice field. A 3-year field experiment was carried out in central China to examine the influence of different fallow season straw management practices on rice yield, soil properties, and emissions of methane (CH4) and nitrous oxide (N2O) from a mono-rice cultivation system. The treatments comprised an unfertilized control (CK), inorganic fertilization (NPK), rice straw burning in situ (NPK + RSB), rice straw mulching (NPK + RSM), and rice straw strip mulching with green manuring (NPK + RSM + GM). The maximum rice yield, soil organic carbon, soil total nitrogen, and available potassium were observed in NPK + RSM + GM treatment. Compared with NPK, the NPK + RSM + GM recorded 9% higher grain yield averaged across 3 years. However, NPK + RSM and NPK + RSB were statistically similar with NPK regarding grain yield. The NPK + RSM and NPK + RSM + GM recorded significantly higher CH4 emission during rice growing season as well as winter fallow; however, the response of N2O emissions was variable. The NPK + RSM and NPK + RSM + GM were statistically similar for annual cumulative CH4 and N2O emissions. The NPK + RSM + GM recorded 103 and 72% higher straw-induced net economic benefits and soil organic carbon sequestration rate, and reduced net global warming potential by 27% as compared with NPK + RSM. Considering the benefits of soil fertility, higher crop productivity, and environmental safety, the NPK + RSM + GM could be the most feasible and sustainable option for mono-rice cultivation system in central China.

Irrigation with oxygen-nanobubble water can reduce methane emission and arsenic dissolution in a flooded rice paddy

A remarkable feature of nanobubbles (<10–6 m in diameter) is their long lifetime in water. Supplying oxygen-nanobubbles (NBs) to continuously flooded paddy soil may retard the development of reductive conditions, thereby reducing the emission of methane (CH4), a potent greenhouse gas, and dissolution of arsenic, an environmental load. We tested this hypothesis by performing a pot experiment and measuring redox-related variables. The NBs were introduced into control water (with properties similar to those of river water) using a commercially available generator. Rice (Oryza sativa L.) growth did not differ between plants irrigated with NB water and those irrigated with control water, but NB water significantly (p < 0.05) reduced cumulative CH4 emission during the rice-growing season by 21%. The amounts of iron, manganese, and arsenic that leached into the drainage water before full rice heading were also reduced by the NB water. Regardless of the water type, weekly-measured CH4 flux was linearly correlated with the leached iron concentration during the rice-growing season (r = 0.74, p < 0.001). At the end of the experiment, the NB water significantly lowered the soil pH in the 0–5 cm layer, probably because of the raised redox potential. The population of methanogenic Archaea (mcrA copy number) in the 0–5 cm layer was significantly increased by the NB water, but we found no correlation between the mcrA copy number and the cumulative CH4 emission (r = –0.08, p = 0.85). In pots without rice plants, soil reduction was not enhanced, regardless of the water type. The results indicate that NB water reduced CH4 emission and arsenic dissolution through an oxidative shift of the redox conditions in the flooded soil. We propose the use of NB water as a tool for controlling redox conditions in flooded paddy soils.

Increase in soil carbon sequestration using rice husk charcoal without stimulating CH4 and N2O emissions in an Andosol paddy field in Japan

Biochar application has been recognized as an effective option for promoting carbon (C) sequestration, but it may also affect the production and consumption of methane (CH4) and nitrous oxide (N2O) in soil. A 1-year field experiment was conducted to investigate the effects of rice husk charcoal application on rice (Oryza sativa L.) productivity and the balance of greenhouse gas exchanges in an Andosol paddy field. The experiment compared the treatments of rice husk charcoal applied at 10, 20 and 40 Mg ha−1 (RC10, RC20 and RC40, respectively), rice husk applied at 20 Mg ha−1 (RH20), and the control (CONT). Rice straw and grain yields did not significantly differ among the treatments. The seasonal cumulative CH4 emissions were 38–47% higher from RC10, RC20 and RC40 than from the CONT. However, the increases were not in proportion to the application rates of rice husk charcoal, and their values did not significantly differ from the CONT. On the contrary, the RH20 treatment significantly increased the cumulative CH4 emission by 227% compared to the CONT. The N2O emissions during the measurement were not affected by the treatments. As a result, the combined global warming potential (GWP) of CH4 and N2O emissions was significantly higher in RH20 than in the other treatments. There was a positive linear correlation between C storage in the top 10 cm of soil and the application rate of rice husk charcoal. The increases in soil C contents compared to the CONT corresponded to 98–149% of the C amounts added as rice husk charcoal and 41% of the C added as rice husk. Carbon dioxide (CO2) fluxes in the off season were not significantly different among RC10, RC20, RC40 and CONT, indicating that C added as rice husk charcoal remained in the soil during the fallow period. The CO2 equivalent balance between soil C sequestration and the combined GWP indicates that the rice husk charcoal treatments stored more C in soil than the CONT, whereas the RH20 emitted more C than the CONT. These results suggest that rice husk charcoal application will contribute to mitigating global warming without sacrificing rice yields.

Effects of N loading rate on CH4 and N2O emissions during cultivation and fallow periods from forage rice fields fertilized with liquid cattle waste

The use of liquid cattle waste (LCW) as a fertilizer for forage rice is important for material recycling because it can promote biomass production, and reduce the use of chemical fertilizer. Meanwhile, increase in emission of greenhouse gases (GHGs), especially CH4 and N2O would be concerned. We conducted a field study to determine the optimum loading rate of LCW as N to promote forage rice growth with lower GHG emissions. The LCW was applied to forage rice fields, N100, N250, N500, and N750, at four different N loading rates of 107, 258, 522, and 786 kg N ha−1, respectively, including 50 kg N ha−1 of basal chemical fertilizer. The above-ground biomass yields increased 14.6–18.5 t ha−1 with increases in N loading rates. During the cultivation period, both the CH4 and N2O fluxes increased with increases in LCW loading rates. In the treatments of N100, N250, N500, and N750, the cumulative CH4 emissions during the entire period, including cultivation and fallow period were 29.6, 18.1, 54.4, and 67.5 kg C ha−1, respectively, whereas those of N2O were −0.15, −0.02, 1.49, and 5.82 kg N ha−1, respectively. Considering the greenhouse gas emissions and above-ground biomass, the yield-scaled CO2-equivalents (CO2-eqs) were 66.3, 35.9, 161, and 272 kg CO2 t−1 for N100, N250, N500, and N750, respectively. These results suggest that N250 is the most appropriate LCW loading rate for promoting forage rice production with lower GHG emissions.

Influence of rice varieties, nitrogen management and planting methods on methane emission and water productivity

A field experiment was conducted during rainy seasons of 2009 and 2010 at New Delhi, India to study the influence of varieties and integrated nitrogen management (INM) on methane (CH4) emission and water productivity under flooded transplanted (FT) and aerobic rice (AR) cultivation. The treatments included two rice (‘PB 1’ and ‘PB 1121’) varieties and eight INM practices including N control, recommended dose of N through urea, different combinations of urea with farmyard manure (FYM), green manure (GM), biofertilizer (BF) and vermicompost (VC). The results showed 91.6–92.5 % lower cumulative CH4 emission in AR compared to FT rice. In aerobic conditions, highest cumulative CH4 emission (6.9–7.0 kg ha−1) was recorded with the application of 100 % N by organic sources (FYM+GM+BF+VC). Global warming potential (GWP) was significantly lower in aerobic rice (105.0–107.5 kg CO2 ha−1) compared to FT rice (1242.5–1447.5 kg CO2 ha−1). Significantly higher amount of water was used in FT rice than aerobic rice by both the rice varieties, and a water saving between 59.5 and 63 % were recorded. Under aerobic conditions, both rice varieties had a water productivity of 8.50–14.69 kg ha−1, whereas in FT rice, it was 3.81–6.00 kg ha−1. In FT rice, a quantity of 1529.2–1725.2 mm water and in aerobic rice 929.2–1225.2 mm water was used to produce one kg rice. Thus, there was a saving of 28.4–39.6 % total water in both the rice varieties under AR cultivation.

Mitigating yield-scaled greenhouse gas emissions through combined application of soil amendments: A comparative study between temperate and subtropical rice paddy soils

Effects of different soil amendments were investigated on methane (CH4) and nitrous oxide (N2O) emissions, global warming potential (GWP) and yield scaled GWPs in paddy soils of Republic of Korea, Japan and Bangladesh. The experimental treatments were NPK only, NPK+fly ash, NPK+silicate slag, NPK+phosphogypsum(PG), NPK+blast furnace slag (BFS), NPK+revolving furnace slag (RFS), NPK+silicate slag (50%)+RFS (50%), NPK+biochar, NPK+biochar+Azolla-cyanobacteria, NPK+silicate slag+Azolla-cyanobacteria, NPK+phosphogypsum (PG)+Azolla-cyanobacteria. The maximum decrease in cumulative seasonal CH4 emissions was recorded 29.7% and 32.6% with Azolla-cyanobacteria plus phospho-gypsum amendments in paddy soils of Japan and Bangladesh respectively, followed by 22.4% and 26.8% reduction with silicate slag plus Azolla-cyanobacteria application. Biochar amendments in paddy soils of Japan and Bangladesh decreased seasonal cumulative N2O emissions by 31.8% and 20.0% respectively, followed by 26.3% and 25.0% reduction with biochar plus Azolla-cyanobacteria amendments. Although seasonal cumulative CH4 emissions were significantly increased by 9.5–14.0% with biochar amendments, however, global warming potentials were decreased by 8.0–12.0% with cyanobacterial inoculation plus biochar amendments. The maximum decrease in GWP was calculated 22.0–30.0% with Azolla-cyanobacteria plus silicate slag amendments. The evolution of greenhouse gases per unit grain yield (yield scaled GWP) was highest in the NPK treatment, which was decreased by 43–50% from the silicate slag and phosphogypsum amendments along with Azolla-cyanobacteria inoculated rice planted soils. Conclusively, it is recommended to incorporate Azolla-cyanobacteria with inorganic and organic amendments for reducing GWP and yield scaled GWP from the rice planted paddy soils of temperate and subtropical countries.

Invasion chronosequence of Spartina alterniflora on methane emission and organic carbon sequestration in a coastal salt marsh

Spartina alterniflora was intentionally introduced to China in 1979 for the purpose of sediment stabilization and dike protection, and has continuously replaced native plants or invaded bare mudflats in the coastal marsh. To evaluate the spatial variation of CH4 emission and soil organic carbon (SOC) storage along the invasion chronosequence, we selected four sites including bare mudflat (Control, as first year invasion), and marshes invaded by S. alterniflora in 2002 (SA-1), 1999 (SA-2) and 1995 (SA-3), respectively, in Sheyang county, Jiangsu, China and set up the marsh mesocosm system for flux measurement. The mean accumulation rate of SOC in the 0–30 cm layer exponentially increased with the invasion time, ranging from 1.08 (over the first 9 years) to 2.35 Mg Cha−1yr−1 (over the period of 12–16 years). The cumulative CH4 emission during the growth season was 20.5, 75.4, 81.0 and 92.2 kg CH4ha−1 in Control, SA-1, SA-2 and SA-3, respectively, and there was a binomial relationship between CH4 emission and invasion time. Cumulative CH4 emission was logarithmically increased with SOC concentration; however the ratio of CH4 emission to SOC concentration was inversely correlated with the invasion time in the S. alterniflora marsh, suggesting that the less increased SOC in the S. alterniflora marsh was converted into CH4. The net global warming potential (GWP) was estimated at 733 kg CO2-eq ha−1yr−1 in the tidal mudflat and reduced to −1273 (SA-1) to −2233 kg CO2-eq ha−1yr−1 (SA-3) in the S. alterniflora marsh. Our results indicated that S. alterniflora invasion effectively sequestrated atmospheric CO2 and mitigated GWP in the coastal marsh of China.

Does richness of emergent plants affect CO2 and CH4 emissions in experimental wetlands?

Summary Plant species richness may affect greenhouse gas emissions because it may change ecosystem productivity. Emergent plants are an important component of wetland ecosystems, but little is known about how emergent plant richness affects greenhouse gas emissions. We assembled experimental communities consisting of 1, 2, 4 or 8 emergent plant species in aquatic microcosms and measured community biomass and emissions of CO2 and CH4. Emergent plant richness had little effect on cumulative emissions of CO2 or CH4, most likely because it did not affect community biomass. This conclusion is supported by the fact that CO2 emission was significantly positively related to community biomass. The reason for the unresponsiveness of community biomass to species richness of emergent plants may be that all the plants are in the same functional group so that complementarity among species is weak. CH4 emissions from monocultures of different species differed greatly. Our results do not support the hypothesis that richness of emergent plants plays an important role in regulating greenhouse gas emissions from wetlands. A significant richness effect on greenhouse gas emissions might be detected in wetlands consisting of different plant functional groups such as emergent, floating and submerged plants.

Effects of biochar application on greenhouse gas emissions, carbon sequestration and crop growth in coastal saline soil

SummaryTo evaluate the benefits of application of biochar to coastal saline soil for climate change mitigation, the effects on soil organic carbon (SOC), greenhouse gases (GHGs) and crop yields were investigated. Biochar was applied at 16 t ha−1 to study its effects on crop growth (Experiment I). The effects of biochar (0, 3.2, 16 and 32 t ha−1) and corn stalk (7.8 t ha−1) on SOC and GHGs were studied using 13C stable isotope technology and a static chamber method, respectively (Experiment II). Biochar increased grain mass per plant of the wheat by 27.7% and increased SOC without influencing non‐biochar SOC. On average, 92.3% of the biochar carbon and 16.8% of corn‐stalk carbon were sequestered into the soil within 1 year. The cumulative emissions of CO2, CH4 and N2O were not affected significantly by biochar but cornstalk application increased N2O emissions by 17.5%. The global warming mitigation potential of the biochar treatments (−3.84 to −3.17 t CO2‐eq. ha−1 t−1 C) was greater than that of the corn stalk treatment (−0.11 t CO2‐eq ha−1 t−1 C). These results suggest that biochar application improves saline soil productivity and soil carbon sequestration without increasing GHG emissions.