Greenhouse gases emission from paddy soil during the fallow season with and without winter flooding in central Japan

Many papers on measurements of greenhouse gases (GHGs) emission in rice paddies during a rice cropping season have been published. During a non-cropping season between Nov. and Apr., we investigated direct and indirect GHGs emissions in rice paddies. The indirect GHGs emission was evaluated as the amount of dissolved gases leaching from the paddy fields. Water management practices for the experiment were (1) continuous flooding (CF) and (2) non-flooding (NF). Although the direct CO₂ emission in the CF treatment was remained nearly zero during the non-cropping period, direct CO₂ emission in the NF treatment was continuously observed throughout the non-cropping period. The concentration of dissolved N₂O in the NF treatment was below the detection limit of the instrument during the non-cropping period except immediately after the flooding and before the drainage. The concentration of dissolved N₂O kept approximately 2 µg L^?1 during the non-cropping period in the CF treatment. The direct CH₄ emission and dissolved CH₄ were not observed during the non-cropping period. Total gas emission in the NF treatment was 10 times as large as that in the CF treatment. Direct CO₂ emission accounted for more than 90 % of the total emission in both treatments.     

Effect of organic,inorganic and slow-release urea fertilisers on CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O emissions from rice paddy fields

Vietnam is one of the world’s top two rice exporting countries. However, rice cultivation is the primary source of agriculture’s greenhouse gas (GHG) emissions in Vietnam. In particular, strategies are required to reduce GHG emissions associated with the application of organic and inorganic fertilisers. The objective of this study was to assess the effects of various combinations of biochar (BIOC), compost (COMP) and slow-release urea (SRU) on methane (CH₄) and nitrous oxide (N₂O) emissions. In total, 1170 gas samples were collected from closed gas chambers in rice paddies at Thinh Long commune and Rang Dong farm in northern Vietnam between June and October 2014. The gas samples were analysed for CH₄-C and N₂O-N fluxes using gas chromatography. The application of BIOC alone resulted in the lowest CH₄ emissions (4.8–59 mg C m^?2 h^?1) and lowest N₂O emissions (0.15–0.26 µg N m^?2 h^?1). The combined application of nitrogen–phosphorus–potassium (NPK) + COMP emitted the highest CH₄ (14–72 mg C m^?2 h^?1), while ½NPK + BIOC emitted the highest N₂O (1.03 µg N m^?2 h^?1 in the TL commune), but it was the second lowest (0.495 µg N m^?2 h^?1) in the RD farm. Green urea and orange urea reduced N₂O emissions significantly (p < 0.05) compared to white urea, but no significant differences were observed with respect to CH₄ emissions. SRU fertilisers and BIOC alone measured the lowest greenhouse gas intensity, i.e. <2.5 and 3 kg CO₂ eq. kg^?1 rice grain, respectively. Based on these results, application of fertilisers in the form of BIOC and/or orange or green urea could be a viable option to reduce both CH₄ and N₂O emissions from rice paddy soils.     

Dry direct-seeding of rice for mitigating greenhouse gas emission: field experimentation and simulation

Conventional puddled transplanted rice (TPR) is a major source of greenhouse gas (GHG), particularly methane, causing global warming. Direct-seeded rice (DSR) is a feasible alternative to mitigate methane emission, besides saving water and labor. A 2-year field experiment was carried out to quantify GHG mitigation and water- and labor-saving potentials of the DSR crop compared to TPR in three villages in Jalandhar district of Punjab, India. The InfoRCT simulation model was used to calculate the emission of CO₂ besides CH₄ and N₂O in different districts of Punjab, India. Total global warming potential (GWP) in transplanted rice in various districts of Punjab ranged from 2.0 to 4.6 t CO₂ eq. ha^?1 and in the DSR it ranged from 1.3 to 2.9 t CO₂ eq. ha^?1. Extrapolation analysis showed that if the entire area under TPR in the state is converted to DSR, the GWP will be reduced by 33 %, and if 50 % area is converted to DSR the GWP will be reduced by 16.6 % of the current emission. The DSR crop saved 3–4 irrigations compared to the transplanted rice without any yield penalty. Human labor use also reduced to 45 % and tractor use to 58 % in the DSR compared to TPR.     

Influence of irrigation frequency on greenhouse gases emission from a paddy soil

Water management is known to be a key factor on methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O) emissions from paddy soils. A field experiment was conducted to study the effect of continuous irrigation (CI) and intermittent irrigation (II) on these emissions. Methane, CO₂, and N₂O emissions from a paddy soil were sampled weekly using a semi-static closed chamber and quantified with the photoacoustic technique from May to November 2011 in Amposta (Ebro Delta, NE Spain). Intermittent irrigation of rice paddies significantly stimulated (N₂O + N₂)–N emission, whereas no substantial N₂O emission was observed when the soil was re-wetted after the dry phase. The cumulative emission of (N₂O + N₂)–N was significantly larger from the II plots (0.73 kg N₂O–N ha^?1 season^–1, P < 0.05) than from the CI plots (?1.40 kg N₂O–N ha^?1 season^?1). Draining prior to harvesting increased N₂O emissions. Draining and flooding cycles controlled CO₂ emission. The cumulative CO₂ emission from II was 8416.35 kg CO₂ ha^?1 season^?1, significantly larger than that from CI (6045.26 kg CO₂ ha^?1 season^?1, P < 0.05). Lower CH₄ emission due to water drainage increased CO₂ emissions. The soil acted as a sink of CH₄ for both types of irrigation. Neither N₂O–N nor CH₄ emissions were affected by soil temperature. Global warming potential was the highest in II (4738.39 kg CO₂ ha^?1) and the lowest in CI (3463.41 kg CO₂ ha^?1). These findings suggest that CI can significantly mitigate the integrative greenhouse effect caused by CH₄ and N₂O from paddy fields while ensuring the highest rice yield.     

Effect of water management on greenhouse gas emissions and microbial properties of paddy soils in Japan and Indonesia

This research aims at elucidating the greenhouse gas emissions and its related soil microbial properties in continuously flooded or intermittently drained paddy soils in Japan and Indonesia. The study in Japan comprises alluvial soil and peat, cultivated to rice variety Nipponbare, while in Indonesia comprised alluvial soil cultivated to rice variety Siam Pandak. Intermittent drainage was performed to half number of the plot in 6 days interval, starting at tillering or heading stage of rice, while the other half number of plot was kept flooded as control. The experiments were carried out to follow the randomized block design with three replications. Gas samples were taken in weekly basis, except during the treatments (i.e., every 2 days interval) and analyzed for methane (CH₄) and nitrous oxide (N₂O) concentrations. Soil samples were and analyzed for the population of methanogenic bacteria, denitrifiers, methane production and consumption potentials, and methanogenic substrate. Plant growth parameters were also observed. The results showed that intermittent drainage significantly reduced greenhouse gas emission from paddy soil of Indonesia and Japan without significant changes in soil microbial population. The reductions of greenhouse emission from Japanese peaty and alluvial paddy soil due to intermittent drained were about 32 and 37%, respectively. Meanwhile, the reductions in greenhouse gas emission from alluvial soil of Indonesia due to intermittent drainage were very similar to that of in Japan, i.e., average about 37%. This suggests that intermittent drainage can be an appropriate technology option to reduce the greenhouse gas emission from paddy soil in Japan and Indonesia.     

Plastic film mulching reduces net greenhouse gas emissions in a rice–rapeseed rotation field

With the aim of assessing differentiation of greenhouse gas emissions as manipulated by plastic film mulching (PFM) from paddy field from a year-round perspective, we determined net ecosystem CO₂ exchange (NEE, CO₂ flux), CH₄ and N₂O fluxes from a rice–rapeseed rotation field. PFM and non-mulching (NM) treatments were set from 2014 to 2017 (May 2014 to April 2015, May 2015 to April 2016 and May 2016 to April 2017 were set as Annual 1, Annual 2 and Annual 3, respectively) in Southwest China. Compared with NM, CH₄ emissions were increased by 60.00% (P?<?0.05), 111.54% (P?<?0.05) and 62.07% (P?<?0.05) under PFM in Annual 1, 2 and 3, respectively. Additionally, PFM delayed the peaks of CH₄ fluxes by 5–10 days during rice season. However, PFM did not affect N₂O emissions on the annual basis. PFM reduced the net carbon loss from soil during rice season while had insignificant influence on soil carbon sequestration capacity during fallow and rapeseed seasons. Overall, the mean annual net ecosystem greenhouse gas exchange among three annuals was 32.11% lower under PFM than under NM. Moreover, PFM slightly increased crop yields of both rice and rapeseed. Accordingly, PFM recommended the suitable agricultural management in the rice–rapeseed rotation field for simultaneously alleviating global warming and maintaining crop yields.

     

Changes in Grain Yield of Rice and Emission of Greenhouse Gases from Paddy Fields after Application of Organic Fertilizers Made from Maize Straw

A field experiment was conducted at the farm of Yangzhou University, Yangzhou, China, to study the effects of organic fertilizers made from maize straw on rice grain yield and the emission of greenhouse gases. Four organic fertilizer treatments were as follows： maize straw （MS）, compost made from maize straw （MC）, methane-generating maize residue （MR）, and black carbon made from maize straw （BC）. These organic fertilizers were applied separately to paddy fields before rice transplanting. No organic fertilizer was applied to the control （CK）. The effects of each organic fertilizer on rice grain yield and emission of greenhouse gases were investigated under two conditions, namely, no nitrogen （N） application （ON） and site-specific N management （SSNM）. Rice grain yields were significantly higher in the MS, MC and MR treatments than those in CK under either ON or SSNM. The MS treatment resulted in the highest grain yield and agronomic N use efficiency. However, no significant difference was observed for these parameters between the BC treatment and CK. The changes in the emissions of methane （CH4） carbon dioxide （CO2）, or nitrous oxide （N20） from the fields were similar among all organic fertilizer treatments during the entire rice growing season. The application of each organic fertilizer significantly increased the emission of each greenhouse gas （except N20 emission in the BC treatment） and global warming potential （GWP）. Emissions of all the greenhouse gases and GWP increased under the same organic fertilizer treatment in the presence of N fertilizer, whereas GWP per unit grain yield decreased. The results indicate that the application of organic fertilizer （MS, MC or MR） could increase grain yield, but also could enhance the emissions of greenhouse gases from paddy fields. High grain yield and environmental efficiency could be achieved by applying SSNM with MR.     

Super Rice Cropping Will Enhance Rice Yield and Reduce CH4 Emission： A Case Study in Nanjing,China

A pot experiment was performed to learn the differences in plant productivity and OH4 emission between two rice cultivars, super rice variety Ningjing 1 and traditional variety Zhendao 11, which were currently commercially appUed in Nanjing, China. Similar seasonal changes of CH4 emission fluxes and soil solution CH4 contents were found between the tested cultivars. Although there was no significant difference in plant biomass production between the cultivars, the grain yield of Ningjing 1 was significantly higher by 35.0% （P 〈 0.05） than that of Zhendao 11, whereas the total CH4 emission from Ningjing 1 was 35.2% lower （P 〈 0.05）. The main difference in the amounts of CH4 emission between the cultivars occurred in the period from the tillering stage to the heading stage. The biomass-scaled and yield-scaled CH4 emissions were respectively 3.8 and 5.2 mg/g for Ningjing 1, significantly lower than those for Zhendao 11 （7.4 and 12.8 mg/g, respectively）. According to the relationships between the plant growth characteristics and the CH4 emission, a stronger root system contributed mainly to the lower CH4 emission of Ningjing 1, as compared with Zhendao 11. Our results demonstrated that super rice has advantages not only in grain productivity but also in CH4 emission mitigation. Further expansion of super rice cropping will enhance rice yield and reduce greenhouse gas emission in China.     

Methane emission from irrigated rice ecosystem: relationship with carbon fixation,partitioning and soil carbon storage

Rice is a major agricultural crop and accounts for 40 % of the total food grain production of India. A field experiment was conducted for two successive seasons (December–June, 2012–13 and December–June, 2013–14) to assess the efficiency of rice varieties for methane (CH₄) emission in relation to atmospheric carbon fixation, partitioning of carbon, and storage in the soil. Six high yielding rice varieties, Bahadur, Cauvery, Dinanath, Joymoti, Kanaklata, and Swarnabh were grown under irrigated condition. Results of the present investigation depicted differences in photosynthetic rate among the varieties accompanied by differential ability for plant biomass partitioning between the shoots and the roots. Stomatal frequency of flag leaf at panicle initiation stage was found to have strong influence on photosynthesis. Low CH₄-emitting rice varieties, Bahadur and Dinanath, were found to have lower size of the xylem vessels than the high CH₄-emitting rice varieties, Joymoti and Kanaklata, and found to influence the CH₄ flux. Soil organic carbon storage of 0.505 Mg C ha^?1 y^?1 in the plough layer of soil (0–15 cm) confirmed that irrigated rice ecosystem is an effective sink of carbon. These findings suggest that selection of suitable rice varieties with higher photosynthetic efficiency and lower emission of CH₄ can be a suitable biological mitigation of this greenhouse gas. Although an inverse relationship of CH₄ with carbon dioxide (CO₂) efflux was observed, irrigated rice ecosystem has a good potential to store substantial amount of carbon in the soil.     

The effect of floating vegetation on CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O emissions from subtropical paddy fields in China

Duckweed (Lemna minor), a floating macrophyte belonging to the Lemnaceae family, is commonly found in subtropical paddy fields. This plant rapidly takes up nutrients from water and forms dense floating mats over the water surface that may impact the biogeochemical processes and greenhouse gas production in paddy fields. In this study, we measured CH₄ and N₂O emissions from duckweed and non-duckweed plots in a subtropical paddy field in China during the period of rice growth using static chamber and gas chromatography methods. Our results showed that CH₄ emission rate ranged from 0.19 to 26.50 mg m^?2 h^?1 in the duckweed plots, and from 1.02 to 28.02 mg m^?2 h^?1 in the non-duckweed plots. The CH₄ emission peak occurred about 1 week earlier in the duckweed plots compared to the non-duckweed counterparts. The mean CH₄ emission rate in the duckweed plots (9.28 mg m^?2 h^?1) was significantly lower than that in non-duckweed plots (11.66 mg m^?2 h^?1) (p < 0.05), which might be attributed to the higher water and soil Eh in the former. N₂O emission rates varied between ?50.11 and 201.82 µg m^?2 h^?1, and between ?28.93 and 54.42 µg m^?2 h^?1 in the duckweed and non-duckweed plots, respectively. The average N₂O emission rate was significantly higher in the duckweed plots than in the non-duckweed plots (40.29 vs. 11.93 µg m^?2 h^?1) (p < 0.05). Our results suggest that the presence of duckweed will reduce CH₄ emission, but increase N₂O flux simultaneously. Taking into account the combined global warming potentials of CH₄ and N₂O, we found that growing duckweed could reduce the overall greenhouse effect of subtropical paddy fields by about 17 %.     

Mitigating N2O and NO Emissions from Direct-Seeded Rice with Nitrification Inhibitor and Urea Deep Placement

Soil-emitted nitrous oxide (N₂O) and nitric oxide (NO) in crop production are harmful nitrogen (N) emissions that may contribute both directly and indirectly to global warming. Application of nitrification inhibitors, such as dicyandiamide (DCD), and urea deep placement (UDP), are considered effective approaches to reduce these emissions. This study investigated the effects of DCD and UDP, compared to urea and potassium nitrate, on emissions, nitrogen use efficiency and grain yields under direct-seeded rice. High-frequency measurements of N₂O and NO emissions were conducted using the automated closed chamber method throughout the crop-growing season and during the ratoon crop. Both UDP and DCD were effective in reducing N₂O emissions by 95% and 73%, respectively. The highest emission factor (1.53% of applied N) was observed in urea, while the lowest was in UDP (0.08%). Emission peaks were mainly associated with fertilization events and appeared within one to two weeks of fertilization. Those emission peaks contributed to 65%–98% of the total seasonal emissions. Residual effects of fertilizer treatments on the N₂O emissions from the ratoon crop were not significant; however, the urea treatment contributed 2%, whereas UDP contributed to 44% of the total annual emissions. On the other hand, cumulative NO emissions were not significant in either the rice or ratoon crops. UDP and DCD increased grain yields by 16%–19% and N recovery efficiency by 30%–40% over urea. The results suggested that the use of DCD and UDP could mitigate N₂O emissions and increase grain yields and nitrogen use efficiency under direct-seeded rice condition.     

Emissions of CH4 and CO2 from paddy fields as affected by tillage practices and crop residues in central China

A field experiment was conducted to investigate effects of tillage practices [no-tillage (NT) and conventional intensive tillage (CT)] and oilseed rape residue returning levels (0, 3000, 6000, 9000 kg dry matter ha^?1) on methane (CH₄) and carbon dioxide (CO₂) emissions and grain yield from paddy fields during the 2011 rice growing season after 2 years oilseed rape-rice rotation in central China. The experiment was established following a split-plot design of a randomized complete block with tillage practices as the main plots and residue returning levels as the sub-plots. NT significantly decreased CO₂ and CH₄ emissions by 38.8 and 27.3 % compared with CT, respectively. Residue returning treatments released significantly more CO₂ and CH₄ by 855.5–10410 and 51.5–210.5 kg ha^?1 than no residue treatments, respectively. The treatments of 3,000 and 6,000 kg ha^?1 residue returning significantly increased rice grain yield by 37.9 and 32.0 % compared with the treatment of no residue returning, respectively. Compared with NT, CT increased yield-scaled emissions of CH₄ and CO₂ by 16.0 %. The treatments of 6,000 and 9,000 kg ha^?1 residue returning significantly increased yield-scaled emissions of CH₄ and CO₂ by 18.1 and 61.5 %, respectively, compared with the treatment of no residue returning. Moreover, the treatment of NT in combination with 3,000 kg ha^?1 residues had the lowest yield-scaled emissions of CH₄ and CO₂ across tillage and residue treatments. In this way, this study revealed that the combination of NT with 3,000 kg ha^?1 residues was a suitable strategy for optimizing carbon emissions and rice grain yield.     

Carbon and Nitrogen Footprints of Major Cereal Crop Production in China: A Study Based on Farm Management Surveys

Greenhouse gas (GHG) emissions and reactive nitrogen (Nr) releases are central environmental problems, which are closely linked to climate change, environmental ecology and crop production. Sustainable development of agriculture plays an important role in GHG emissions and Nr loss. The life cycle assessment (LCA) method was used to calculate the product and farm carbon footprints (CFs) and nitrogen footprints (NFs) in rice, wheat and maize production in China based on farm survey data. The results pinpointed that the CFs of rice, wheat and maize were 0.87, 0.30 and 0.24 kg/kg. Meanwhile, the computed NFs were 17.11, 14.26 and 6.83 g/kg, respectively. Synthetic nitrogen fertilizer applications and methane (CH₄) emissions were dominant CF sources, while ammonia (NH₃) volatilization was the main NF contributor. Moreover, significant decreases in CF and NF by 20%–54% and 33%–61%, respectively, were found in large-size farms (> 20 hm²) when compared to small-size farms (< 0.7 hm²). Furthermore, the significantly positive relationships between CF and NF indicated the potential for simultaneous mitigation in the regions with high agricultural inputs, like amounts of fertilizer. Based on our results, some effective solutions would be favorable toward mitigating climate change and eutrophication of the major cereal crop production in China, especially optimizing fertilizer use and farm machinery operation efficiencies, as well as developing large-size farms with intensive farming.     

Intercropping of orchardgrass and alfalfa improves soil fertility,forage yield,feeding values and land use efficiency while limiting ruminal greenhouse gas emissions

Intercropping has been a globally accepted practice for forage production, however, consideration of multiple performance criteria for intercropping including forage production, feed use efficiency and ruminal greenhouse gas emissions needs to be further investigated. A two-year field study was conducted to evaluate forage dry matter (DM) yield, nutritive value, feeding values and land-use efficiency as well as ruminal carbon dioxide (CO₂) and methane (CH₄) emissions of intercropped orchardgrass (Dactylis glomerata) and alfalfa (Medicago sativa) sown in five intercropping ratios (100:0, 75:25, 50:50, 25:75, and 0:100, based on seed weight) and three nitrogen (N) fertilizer levels (0, 50, and 100 kg ha⁻¹). Increasing alfalfa proportion and N fertilizer level increased soil nutrients and the two-year total DM yield. Intercropping increased both land and nitrogen use efficiency (NUE) compared with monocultures. Greater NUE was obtained when N fertilizer was applied at 50 kg ha⁻¹, compared with 100 kg ha⁻¹. Increasing the proportion of alfalfa in intercrops increased the crude protein yield and rumen undegraded protein yield. Harvested forage intercrops were incubated with ruminal fluid for 48 h. Degraded DM yield, CO₂ and CH₄ emissions increased with increasing alfalfa proportion in intercrops. Overall, the 75:25 of orchardgrass-alfalfa intercrops was recommended as the best compromise between high forage productivity, superior feed use efficiency and low ruminal greenhouse gas emissions through complementary effects. The results indicate that the appropriate N fertilization level would be 50 kg ha⁻¹ for acquiring higher nitrogen use efficiency and forage productivity.     

Policy measures to promote mid-summer drainage in paddy fields for a reduction in methane gas emissions: the application of a dynamic,spatial computable general equilibrium model

Rice production is affected by climate change, while climate change is simultaneously accelerated by methane gas (CH₄) emissions from paddy fields. The rice sector must take suitable mitigation measures, such as prolonging mid-summer drainage (MSD) before the rice flowering period. To propose a mitigation policy, this study aims to demonstrate the environmental and economic effects of MSD in Japanese paddy fields by using a dynamic, spatial computable general equilibrium (CGE) model and crop model; the study also considers environmental subsidies with a carbon tax scheme to promote MSD measures. The results demonstrate that climate change under the 8.5 representative concentration pathway (RCP) scenario will reduce rice prices and rice farmers’ nominal income due to bumper harvests until the 2050s. Promoting MSD in paddy fields can prevent a decrease in farmers’ nominal income and effectively reduce CH₄ emissions if all farmers adopt this measure. However, some farmers can potentially increase their own yield by avoiding MSD under high rice prices, which would be maintained through other farmers’ participation. A strong motivation exists for some farmers to gain a “free ride,” and an environmental subsidy with a carbon tax can help motivate farmers to adopt MSD. Therefore, the policy mix of prolonging MSD and environmental subsidies can increase all farmers’ incomes by preventing “free rides” and decrease greenhouse gas emissions with a slight decrease in Japan’s GDP.

     

浅埋滴灌条件下优化施氮对春玉米田温室气体排放的影响

以传统漫灌常规常量追氮为对照（CK）,采用静态暗箱-气相色谱法测定浅埋滴灌下常量追氮（T₁）和优化追氮（T₂：70%常量追氮）春玉米田生育期内CO₂、N₂O和CH₄排放特征,探究西辽河平原浅埋滴灌条件下优化施氮对春玉米田土壤温室气体排放的影响。结果表明,T₁和T₂处理玉米产量无显著差异,均显著高于CK（P<0.05）。相同施氮量下,浅埋滴灌相比传统漫灌N₂O排放量增加11.78%,CH₄吸收量降低34.78%;T₂较T₁处理CO₂和N₂O排放量分别减少13.15%和20.27%。相同施氮量下,与CK相比,T₁处理降低了温室气体排放强度（GHGI）（P<0.05）,浅埋滴灌T₂处理GHGI较T₁处理降低10.46%;CK和T₁处理综合增温潜势（GWP）均显著高于T₂（P<0.05）;T₁和T₂处理净生态系统经济预算（NEEB）均显著高于CK（P<0.05）。综合来看,浅埋滴灌下T₂处理,既降低了GHGI和GWP,又保证了较高玉米产量和NEEB,是西辽河平原玉米兼顾高产、高效和生态的水氮管理模式。     

Global warming impacts of the process to utilize digested slurry from methane fermentation as a fertilizer: Case Study of the Yamada Biomass Plant

Greenhouse gas (GHG) emissions from the process to utilize digested slurry from methane fermentation as a fertilizer were calculated with actual operational data from a methane fermentation plant and the effects were verified by introducing the process into a field system. The results indicated that the total emissions from the utilization of digested slurry as a fertilizer were 8.1 kg-CO₂ eq. per 1 ton of digested slurry and transportation was the major source of GHG emissions, accounting for 67 % of the total emissions. Shortening the transportation distance by using digested slurry in farmlands near the methane fermentation plant is the most effective to reduce GHG emissions. The results also indicated that GHG emissions from the wastewater treatment process for digested slurry were much larger than GHG emissions from the utilization of digested slurry as a fertilizer. In conclusion, CH₄ as an energy source and digested slurry as a fertilizer can be effectively utilized and reduce GHG emissions by introducing the methane fermentation processes to the use of digested slurry as a fertilizer.

     

Global warming impacts of the process to utilize digested slurry from methane fermentation as a fertilizer: Case Study of the Yamada Biomass Plant

Greenhouse gas (GHG) emissions from the process to utilize digested slurry from methane fermentation as a fertilizer were calculated with actual operational data from a methane fermentation plant and the effects were verified by introducing the process into a field system. The results indicated that the total emissions from the utilization of digested slurry as a fertilizer were 8.1 kg-CO₂ eq. per 1 ton of digested slurry and transportation was the major source of GHG emissions, accounting for 67 % of the total emissions. Shortening the transportation distance by using digested slurry in farmlands near the methane fermentation plant is the most effective to reduce GHG emissions. The results also indicated that GHG emissions from the wastewater treatment process for digested slurry were much larger than GHG emissions from the utilization of digested slurry as a fertilizer. In conclusion, CH₄ as an energy source and digested slurry as a fertilizer can be effectively utilized and reduce GHG emissions by introducing the methane fermentation processes to the use of digested slurry as a fertilizer.     

Lasting effects of controlled irrigation during rice-growing season on nitrous oxide emissions from winter wheat croplands in Southeast China

Nitrous oxide (N₂O) emission from croplands in China is a serious environmental concern. Water management is an important factor in regulating N₂O emissions from croplands. In China, controlled irrigation (CI) is one mode of the water-saving irrigation for rice and is widely used. This study aims to assess the lasting effects of CI on N₂O emissions from winter wheat croplands in Southeast China, with traditional irrigation (TI) as the control. CI performed during the rice-growing season had obvious lasting effects on N₂O emissions of the subsequent winter wheat-growing season. Compared with TI, CI significantly increased the cumulative N₂O emission by 129.1 % during the rice-growing season (p < 0.05), but significantly decreased it by 47.7 % during the wheat season (p < 0.05). Continuous flooding of the TI during most of the rice-growing season resulted in an increase in N₂O emissions during the winter wheat-growing season. Over the whole annual cycle, the cumulative N₂O emission from the plots under CI during the rice-growing season was 5.3 kg N₂O–N ha^?1, which was 103.2 % of that under TI (p > 0.05). The results suggest that CI does not significantly increase the cumulative N₂O emission from the rice–winter wheat rotation systems while insuring rice and wheat yields. This study focuses on the lasting effects of water-saving irrigation mode during rice-growing season on N₂O emissions during the following wheat-growing season. Thus, it is a development and complement of the previous researches on the effects of water-saving irrigation on N₂O emissions from rice–winter wheat rotation croplands.     

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.